index : litmus-rt.git	archive/unc-master-3.0 archived-2013.1 archived-private-master archived-semi-part demo ecrts-pgm-final ecrts14-pgm-final gpusync-rtss12 gpusync/staging linux-tip litmus2008-patch-series master pgm prop/litmus-signals prop/robust-tie-break staging test tracing-devel v2.6.34-with-arm-patches v2015.1 wip-2011.2-bbb wip-2011.2-bbb-trace wip-2012.3-gpu wip-2012.3-gpu-preport wip-2012.3-gpu-rtss13 wip-2012.3-gpu-sobliv-budget-w-kshark wip-aedzl-final wip-aedzl-revised wip-arbit-deadline wip-aux-tasks wip-bbb wip-bbb-prio-don wip-better-break wip-binary-heap wip-budget wip-color wip-color-jlh wip-d10-hz1000 wip-default-clustering wip-dissipation-jerickso wip-dissipation2-jerickso wip-ecrts14-pgm wip-edf-hsb wip-edf-os wip-edf-tie-break wip-edzl-critique wip-edzl-final wip-edzl-revised wip-events wip-extra-debug wip-fix-switch-jerickso wip-fix3 wip-fmlp-dequeue wip-ft-irq-flag wip-gpu-cleanup wip-gpu-interrupts wip-gpu-rtas12 wip-gpu-rtss12 wip-gpu-rtss12-srp wip-gpusync-merge wip-ikglp wip-k-fmlp wip-kernel-coloring wip-kernthreads wip-klmirqd-to-aux wip-kshark wip-litmus-3.2 wip-litmus2011.2 wip-litmus3.0-2011.2 wip-master-2.6.33-rt wip-mc wip-mc-bipasa wip-mc-jerickso wip-mc2-cache-slack wip-mcrit-mac wip-merge-3.0 wip-merge-v3.0 wip-migration-affinity wip-mmap-uncache wip-modechange wip-nested-locking wip-omlp-gedf wip-pai wip-percore-lib wip-performance wip-pgm wip-pgm-split wip-pm-ovd wip-prio-inh wip-prioq-dgl wip-refactored-gedf wip-release-master-fix wip-robust-tie-break wip-rt-kshark wip-rtas12-pgm wip-semi-part wip-semi-part-edfos-jerickso wip-shared-lib wip-shared-lib2 wip-shared-mem wip-splitting-jerickso wip-splitting-omlp-jerickso wip-stage-binheap wip-sun-port wip-timer-trace wip-tracepoints
	The LITMUS^RT kernel.	Bjoern Brandenburg

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Branch	Commit message	Author	Age
archive/unc-master-3.0	P-FP: fix BUG_ON releated to priority inheritance	Bjoern Brandenburg	13 years
archived-2013.1	uncachedev: mmap memory that is not cached by CPUs	Glenn Elliott	12 years
archived-private-master	Merge branch 'wip-2.6.34' into old-private-master	Andrea Bastoni	15 years
archived-semi-part	Merge branch 'wip-semi-part' of ssh://cvs/cvs/proj/litmus/repo/litmus2010 int...	Andrea Bastoni	15 years
demo	Further refinements	Jonathan Herman	14 years
ecrts-pgm-final	Merge branch 'wip-ecrts14-pgm' of ssh://rtsrv.cs.unc.edu/home/litmus/litmus-r...	Glenn Elliott	12 years
ecrts14-pgm-final	Merge branch 'wip-ecrts14-pgm' of ssh://rtsrv.cs.unc.edu/home/litmus/litmus-r...	Glenn Elliott	12 years
gpusync-rtss12	Final GPUSync implementation.	Glenn Elliott	12 years
gpusync/staging	Rename IKGLP R2DGLP.	Glenn Elliott	12 years
linux-tip	Merge branch 'slab/urgent' of git://git.kernel.org/pub/scm/linux/kernel/git/p...	Linus Torvalds	15 years
litmus2008-patch-series	add i386 feather-trace implementation	Bjoern B. Brandenburg	16 years
master	PSN-EDF: use inferred_sporadic_job_release_at	Bjoern Brandenburg	9 years
pgm	make it compile	Glenn Elliott	12 years
prop/litmus-signals	Infrastructure for Litmus signals.	Glenn Elliott	13 years
prop/robust-tie-break	Fixed bug in edf_higher_prio().	Glenn Elliott	13 years
staging	Fix tracepoint compilation error	Felipe Cerqueira	13 years
test	9/23/2016	Namhoon Kim	9 years
tracing-devel	Test kernel tracing events capabilities	Andrea Bastoni	16 years
v2.6.34-with-arm-patches	smsc911x: Add spinlocks around registers access	Catalin Marinas	15 years
v2015.1	Add ARM syscall def for get_current_budget	Bjoern Brandenburg	10 years
wip-2011.2-bbb	Litmus core: simplify np-section protocol	Bjoern B. Brandenburg	14 years
wip-2011.2-bbb-trace	Refactor sched_trace_log_message() -> debug_trace_log_message()	Andrea Bastoni	14 years
wip-2012.3-gpu	SOBLIV draining support for C-EDF.	Glenn Elliott	12 years
wip-2012.3-gpu-preport	pick up last C-RM file	Glenn Elliott	12 years
wip-2012.3-gpu-rtss13	Fix critical bug in GPU tracker.	Glenn Elliott	12 years
wip-2012.3-gpu-sobliv-budget-w-kshark	Proper sobliv draining and many bug fixes.	Glenn Elliott	12 years
wip-aedzl-final	Make it easier to compile AEDZL interfaces in liblitmus.	Glenn Elliott	15 years
wip-aedzl-revised	Add sched_trace data for Apative EDZL	Glenn Elliott	15 years
wip-arbit-deadline	Fix compilation bug.	Glenn Elliott	13 years
wip-aux-tasks	Description of refined aux task inheritance.	Glenn Elliott	13 years
wip-bbb	GSN-EDF & Core: improve debug TRACE'ing for NP sections	Bjoern B. Brandenburg	14 years
wip-bbb-prio-don	use correct timestamp	Bjoern B. Brandenburg	14 years
wip-better-break	Implement hash-based EDF tie-breaking.	Glenn Elliott	13 years
wip-binary-heap	Make C-EDF work with simplified binheap_delete	Glenn Elliott	13 years
wip-budget	Added support for choices in budget policy enforcement.	Glenn Elliott	15 years
wip-color	Summarize schedulability with final record	Jonathan Herman	13 years
wip-color-jlh	sched_color: Fixed two bugs causing crashing on experiment restart and a rare...	Jonathan Herman	13 years
wip-d10-hz1000	Enable HZ=1000 on District 10	Bjoern B. Brandenburg	15 years
wip-default-clustering	Feature: Make default C-EDF clustering compile-time configurable.	Glenn Elliott	15 years
wip-dissipation-jerickso	Update from 2.6.36 to 2.6.36.4	Jeremy Erickson	11 years
wip-dissipation2-jerickso	Update 2.6.36 to 2.6.36.4	Jeremy Erickson	11 years
wip-ecrts14-pgm	Merge branch 'wip-ecrts14-pgm' of ssh://rtsrv.cs.unc.edu/home/litmus/litmus-r...	Glenn Elliott	12 years
wip-edf-hsb	last tested version	Jonathan Herman	14 years
wip-edf-os	Lookup table EDF-os	Jeremy Erickson	12 years
wip-edf-tie-break	Merge branch 'wip-edf-tie-break' of ssh://rtsrv.cs.unc.edu/home/litmus/litmus...	Glenn Elliott	13 years
wip-edzl-critique	Use hr_timer's active checks instead of having own flag.	Glenn Elliott	15 years
wip-edzl-final	Implementation of the EDZL scheduler.	Glenn Elliott	15 years
wip-edzl-revised	Clean up comments.	Glenn Elliott	15 years
wip-events	Added support for tracing arbitrary actions.	Jonathan Herman	15 years
wip-extra-debug	DBG: add additional tracing	Bjoern B. Brandenburg	15 years
wip-fix-switch-jerickso	Attempt to fix race condition with plugin switching	Jeremy Erickson	15 years
wip-fix3	sched: show length of runqueue clock deactivation in /proc/sched_debug	Bjoern B. Brandenburg	15 years
wip-fmlp-dequeue	Improve FMLP queue management.	Glenn Elliott	14 years
wip-ft-irq-flag	Feather-Trace: keep track of interrupt-related interference.	Bjoern B. Brandenburg	14 years
wip-gpu-cleanup	Enable sched_trace log injection from userspace	Glenn Elliott	13 years
wip-gpu-interrupts	Remove option for threading of all softirqs.	Glenn Elliott	14 years
wip-gpu-rtas12	Generalized GPU cost predictors + EWMA. (untested)	Glenn Elliott	13 years
wip-gpu-rtss12	Final GPUSync implementation.	Glenn Elliott	13 years
wip-gpu-rtss12-srp	experimental changes to support GPUs under SRP	Glenn Elliott	13 years
wip-gpusync-merge	Cleanup priority tracking for budget enforcement.	Glenn Elliott	11 years
wip-ikglp	Move RSM and IKGLP imp. to own .c files	Glenn Elliott	13 years
wip-k-fmlp	Merge branch 'mpi-master' into wip-k-fmlp	Glenn Elliott	14 years
wip-kernel-coloring	Added recolor syscall	Namhoon Kim	7 years
wip-kernthreads	Kludge work-queue processing into klitirqd.	Glenn Elliott	15 years
wip-klmirqd-to-aux	Allow klmirqd threads to be given names.	Glenn Elliott	13 years
wip-kshark	Merge branch 'mpi-staging' into wip-kshark	Jonathan Herman	13 years
wip-litmus-3.2	Merge commit 'v3.2' into litmus-staging	Andrea Bastoni	13 years
wip-litmus2011.2	Cleanup: Coding conformance for affinity stuff.	Glenn Elliott	14 years
wip-litmus3.0-2011.2	Feather-Trace: keep track of interrupt-related interference.	Bjoern B. Brandenburg	14 years
wip-master-2.6.33-rt	Avoid deadlock when switching task policy to BACKGROUND (ugly)	Andrea Bastoni	15 years
wip-mc	Removed ARM-specific hacks which disabled less common mixed-criticality featu...	Jonathan Herman	12 years
wip-mc-bipasa	MC-EDF added	bipasa chattopadhyay	13 years
wip-mc-jerickso	Split C/D queues	Jeremy Erickson	15 years
wip-mc2-cache-slack	Manually patched mc^2 related code	Ming Yang	10 years
wip-mcrit-mac	cosmetic	Mac Mollison	15 years
wip-merge-3.0	Prevent Linux to send IPI and queue tasks on remote CPUs.	Andrea Bastoni	14 years
wip-merge-v3.0	Prevent Linux to send IPI and queue tasks on remote CPUs.	Andrea Bastoni	14 years
wip-migration-affinity	NULL affinity dereference in C-EDF.	Glenn Elliott	14 years
wip-mmap-uncache	share branch with others	Glenn Elliott	13 years
wip-modechange	RTSS 2017 submission	Namhoon Kim	8 years
wip-nested-locking	Appears to be working.	Bryan Ward	12 years
wip-omlp-gedf	First implementation of G-OMLP.	Glenn Elliott	15 years
wip-pai	Some cleanup of PAI	Glenn Elliott	14 years
wip-percore-lib	9/21/2016	Namhoon Kim	9 years
wip-performance	CONFIG_DONT_PREEMPT_ON_TIE: Don't preeempt a scheduled task on priority tie.	Glenn Elliott	14 years
wip-pgm	Add PGM support to C-FL	Glenn Elliott	12 years
wip-pgm-split	First draft of C-FL-split	Namhoon Kim	12 years
wip-pm-ovd	Add preemption-and-migration overhead tracing support	Andrea Bastoni	15 years
wip-prio-inh	P-EDF updated to use the generic pi framework.	Glenn Elliott	15 years
wip-prioq-dgl	BUG FIX: Support DGLs with PRIOQ_MUTEX	Glenn Elliott	13 years
wip-refactored-gedf	Generalizd architecture for GEDF-style scheduelrs to reduce code redundancy.	Glenn Elliott	15 years
wip-release-master-fix	bugfix: release master CPU must signal task was picked	Bjoern B. Brandenburg	14 years
wip-robust-tie-break	EDF priority tie-breaks.	Glenn Elliott	13 years
wip-rt-kshark	Move task time accounting into the complete_job method.	Jonathan Herman	13 years
wip-rtas12-pgm	Scheduling of PGM jobs.	Glenn Elliott	13 years
wip-semi-part	Fix compile error with newer GCC	Jeremy Erickson	12 years
wip-semi-part-edfos-jerickso	Use initial CPU set by client	Jeremy Erickson	12 years
wip-shared-lib	TODO: Fix condition checks in replicate_page_move_mapping()	Namhoon Kim	9 years
wip-shared-lib2	RTAS 2017 Submission ver.	Namhoon Kim	9 years
wip-shared-mem	Initial commit for shared library	Namhoon Kim	9 years
wip-splitting-jerickso	Fix release behavior	Jeremy Erickson	13 years
wip-splitting-omlp-jerickso	Bjoern's Dissertation Code with Priority Donation	Jeremy Erickson	13 years
wip-stage-binheap	An efficient binary heap implementation.	Glenn Elliott	13 years
wip-sun-port	Dynamic memory allocation and clean exit for FeatherTrace	Christopher Kenna	15 years
wip-timer-trace	bugfix: C-EDF, clear scheduled field of the correct CPU upon task_exit	Andrea Bastoni	15 years
wip-tracepoints	Add kernel-style events for sched_trace_XXX() functions	Andrea Bastoni	14 years
Tag	Download	Author	Age
2015.1	commit 8e51b37822...	Bjoern Brandenburg	10 years
2013.1	commit bcaacec1ca...	Glenn Elliott	12 years
2012.3	commit c158b5fbe4...	Jonathan Herman	13 years
2012.2	commit b53c479a0f...	Glenn Elliott	13 years
2012.1	commit 83b11ea1c6...	Bjoern B. Brandenburg	14 years
rtas12-mc-beta-exp	commit 8e236ee20f...	Christopher Kenna	14 years
2011.1	commit d11808b5c6...	Christopher Kenna	15 years
v2.6.37-rc4	commit e8a7e48bb2...	Linus Torvalds	15 years
v2.6.37-rc3	commit 3561d43fd2...	Linus Torvalds	15 years
v2.6.37-rc2	commit e53beacd23...	Linus Torvalds	15 years
v2.6.37-rc1	commit c8ddb2713c...	Linus Torvalds	15 years
v2.6.36	commit f6f94e2ab1...	Linus Torvalds	15 years
2010.2	commit 5c5456402d...	Bjoern B. Brandenburg	15 years
v2.6.36-rc8	commit cd07202cc8...	Linus Torvalds	15 years
v2.6.36-rc7	commit cb655d0f3d...	Linus Torvalds	15 years
v2.6.36-rc6	commit 899611ee7d...	Linus Torvalds	15 years
v2.6.36-rc5	commit b30a3f6257...	Linus Torvalds	15 years
v2.6.36-rc4	commit 49553c2ef8...	Linus Torvalds	15 years
v2.6.36-rc3	commit 2bfc96a127...	Linus Torvalds	15 years
v2.6.36-rc2	commit 76be97c1fc...	Linus Torvalds	15 years
v2.6.36-rc1	commit da5cabf80e...	Linus Torvalds	15 years
v2.6.35	commit 9fe6206f40...	Linus Torvalds	15 years
v2.6.35-rc6	commit b37fa16e78...	Linus Torvalds	15 years
v2.6.35-rc5	commit 1c5474a65b...	Linus Torvalds	15 years
v2.6.35-rc4	commit 815c4163b6...	Linus Torvalds	15 years
v2.6.35-rc3	commit 7e27d6e778...	Linus Torvalds	15 years
v2.6.35-rc2	commit e44a21b726...	Linus Torvalds	15 years
v2.6.35-rc1	commit 67a3e12b05...	Linus Torvalds	15 years
2010.1	commit 7c1ff4c544...	Andrea Bastoni	15 years
v2.6.34	commit e40152ee1e...	Linus Torvalds	15 years
v2.6.33.4	commit 4640b4e7d9...	Greg Kroah-Hartman	15 years
v2.6.34-rc7	commit b57f95a382...	Linus Torvalds	15 years
v2.6.34-rc6	commit 66f41d4c5c...	Linus Torvalds	15 years
v2.6.33.3	commit 3e7ad8ed97...	Greg Kroah-Hartman	15 years
v2.6.34-rc5	commit 01bf0b6457...	Linus Torvalds	15 years
v2.6.34-rc4	commit 0d0fb0f9c5...	Linus Torvalds	15 years
v2.6.33.2	commit 19f00f070c...	Greg Kroah-Hartman	15 years
v2.6.34-rc3	commit 2eaa9cfdf3...	Linus Torvalds	15 years
v2.6.34-rc2	commit 220bf991b0...	Linus Torvalds	15 years
v2.6.33.1	commit dbdafe5ccf...	Greg Kroah-Hartman	15 years
v2.6.34-rc1	commit 57d54889cd...	Linus Torvalds	16 years
v2.6.33	commit 60b341b778...	Linus Torvalds	16 years
v2.6.33-rc8	commit 724e6d3fe8...	Linus Torvalds	16 years
v2.6.33-rc7	commit 29275254ca...	Linus Torvalds	16 years
v2.6.33-rc6	commit abe94c756c...	Linus Torvalds	16 years
v2.6.33-rc5	commit 92dcffb916...	Linus Torvalds	16 years
v2.6.33-rc4	commit 7284ce6c9f...	Linus Torvalds	16 years
v2.6.33-rc3	commit 74d2e4f8d7...	Linus Torvalds	16 years
v2.6.33-rc2	commit 6b7b284958...	Linus Torvalds	16 years
v2.6.33-rc1	commit 55639353a0...	Linus Torvalds	16 years
v2.6.32	commit 22763c5cf3...	Linus Torvalds	16 years
v2.6.32-rc8	commit 648f4e3e50...	Linus Torvalds	16 years
v2.6.32-rc7	commit 156171c71a...	Linus Torvalds	16 years
v2.6.32-rc6	commit b419148e56...	Linus Torvalds	16 years
v2.6.32-rc5	commit 012abeea66...	Linus Torvalds	16 years
v2.6.32-rc4	commit 161291396e...	Linus Torvalds	16 years
v2.6.32-rc3	commit 374576a8b6...	Linus Torvalds	16 years
v2.6.32-rc1	commit 17d857be64...	Linus Torvalds	16 years
v2.6.32-rc2	commit 17d857be64...	Linus Torvalds	16 years
v2.6.31	commit 74fca6a428...	Linus Torvalds	16 years
v2.6.31-rc9	commit e07cccf404...	Linus Torvalds	16 years
v2.6.31-rc8	commit 326ba5010a...	Linus Torvalds	16 years
v2.6.31-rc7	commit 422bef879e...	Linus Torvalds	16 years
v2.6.31-rc6	commit 64f1607ffb...	Linus Torvalds	16 years
v2.6.31-rc5	commit ed680c4ad4...	Linus Torvalds	16 years
v2.6.31-rc4	commit 4be3bd7849...	Linus Torvalds	16 years
v2.6.31-rc3	commit 6847e154e3...	Linus Torvalds	16 years
v2.6.31-rc2	commit 8e4a718ff3...	Linus Torvalds	16 years
v2.6.31-rc1	commit 28d0325ce6...	Linus Torvalds	16 years
v2.6.30	commit 07a2039b8e...	Linus Torvalds	16 years
v2.6.30-rc8	commit 9fa7eb283c...	Linus Torvalds	16 years
v2.6.30-rc7	commit 59a3759d0f...	Linus Torvalds	16 years
v2.6.30-rc6	commit 1406de8e11...	Linus Torvalds	16 years
v2.6.30-rc5	commit 091bf7624d...	Linus Torvalds	16 years
v2.6.30-rc4	commit 091438dd56...	Linus Torvalds	16 years
v2.6.30-rc3	commit 0910697403...	Linus Torvalds	16 years
v2.6.30-rc2	commit 0882e8dd3a...	Linus Torvalds	16 years
v2.6.30-rc1	commit 577c9c456f...	Linus Torvalds	16 years
v2.6.29	commit 8e0ee43bc2...	Linus Torvalds	16 years
v2.6.29-rc8	commit 041b62374c...	Linus Torvalds	17 years
v2.6.29-rc7	commit fec6c6fec3...	Linus Torvalds	17 years
v2.6.29-rc6	commit 20f4d6c3a2...	Linus Torvalds	17 years
v2.6.29-rc5	commit d2f8d7ee1a...	Linus Torvalds	17 years
v2.6.29-rc4	commit 8e4921515c...	Linus Torvalds	17 years
v2.6.29-rc3	commit 18e352e4a7...	Linus Torvalds	17 years
v2.6.29-rc2	commit 1de9e8e70f...	Linus Torvalds	17 years
v2.6.29-rc1	commit c59765042f...	Linus Torvalds	17 years
v2.6.28	commit 4a6908a3a0...	Linus Torvalds	17 years
v2.6.28-rc9	commit 929096fe9f...	Linus Torvalds	17 years
v2.6.28-rc8	commit 8b1fae4e42...	Linus Torvalds	17 years
v2.6.28-rc7	commit 061e41fdb5...	Linus Torvalds	17 years
v2.6.28-rc6	commit 13d428afc0...	Linus Torvalds	17 years
v2.6.28-rc5	commit 9bf1a2445f...	Linus Torvalds	17 years
v2.6.28-rc4	commit f7160c7573...	Linus Torvalds	17 years
v2.6.28-rc3	commit 45beca08dd...	Linus Torvalds	17 years
v2.6.28-rc2	commit 0173a3265b...	Linus Torvalds	17 years
v2.6.28-rc1	commit 57f8f7b60d...	Linus Torvalds	17 years
v2.6.27	commit 3fa8749e58...	Linus Torvalds	17 years
v2.6.27-rc9	commit 4330ed8ed4...	Linus Torvalds	17 years
v2.6.27-rc8	commit 94aca1dac6...	Linus Torvalds	17 years
v2.6.27-rc7	commit 72d31053f6...	Linus Torvalds	17 years
v2.6.27-rc6	commit adee14b2e1...	Linus Torvalds	17 years
v2.6.27-rc5	commit 24342c34a0...	Linus Torvalds	17 years
v2.6.27-rc4	commit 6a55617ed5...	Linus Torvalds	17 years
v2.6.27-rc3	commit 30a2f3c60a...	Linus Torvalds	17 years
v2.6.27-rc2	commit 0967d61ea0...	Linus Torvalds	17 years
v2.6.27-rc1	commit 6e86841d05...	Linus Torvalds	17 years
v2.6.26	commit bce7f793da...	Linus Torvalds	17 years
v2.6.26-rc9	commit b7279469d6...	Linus Torvalds	17 years
v2.6.26-rc8	commit 543cf4cb3f...	Linus Torvalds	17 years
v2.6.26-rc7	commit d70ac829b7...	Linus Torvalds	17 years
v2.6.26-rc6	commit 5dd34572ad...	Linus Torvalds	17 years
v2.6.26-rc5	commit 53c8ba9540...	Linus Torvalds	17 years
v2.6.26-rc4	commit e490517a03...	Linus Torvalds	17 years
v2.6.26-rc3	commit b8291ad07a...	Linus Torvalds	17 years
v2.6.26-rc2	commit 492c2e476e...	Linus Torvalds	17 years
v2.6.26-rc1	commit 2ddcca36c8...	Linus Torvalds	17 years
v2.6.25	commit 4b119e21d0...	Linus Torvalds	17 years
v2.6.25-rc9	commit 120dd64cac...	Linus Torvalds	17 years
v2.6.25-rc8	commit 0e81a8ae37...	Linus Torvalds	17 years
v2.6.25-rc7	commit 05dda977f2...	Linus Torvalds	17 years
v2.6.25-rc6	commit a978b30af3...	Linus Torvalds	17 years
v2.6.25-rc5	commit cdeeeae056...	Linus Torvalds	18 years
v2.6.25-rc4	commit 29e8c3c304...	Linus Torvalds	18 years
v2.6.25-rc3	commit bfa274e243...	Linus Torvalds	18 years
v2.6.25-rc2	commit 101142c37b...	Linus Torvalds	18 years
v2.6.25-rc1	commit 19af35546d...	Linus Torvalds	18 years
v2.6.24	commit 49914084e7...	Linus Torvalds	18 years
v2.6.24-rc8	commit cbd9c88369...	Linus Torvalds	18 years
v2.6.24-rc7	commit 3ce5445046...	Linus Torvalds	18 years
v2.6.24-rc6	commit ea67db4cdb...	Linus Torvalds	18 years
v2.6.24-rc5	commit 82d29bf6dc...	Linus Torvalds	18 years
v2.6.24-rc4	commit 09b56adc98...	Linus Torvalds	18 years
v2.6.24-rc3	commit d9f8bcbf67...	Linus Torvalds	18 years
v2.6.24-rc2	commit dbeeb816e8...	Linus Torvalds	18 years
v2.6.24-rc1	commit c9927c2bf4...	Linus Torvalds	18 years
v2.6.23	commit bbf25010f1...	Linus Torvalds	18 years
v2.6.23-rc9	commit 3146b39c18...	Linus Torvalds	18 years
v2.6.23-rc8	commit 4942de4a0e...	Linus Torvalds	18 years
v2.6.23-rc7	commit 81cfe79b9c...	Linus Torvalds	18 years
v2.6.23-rc6	commit 0d4cbb5e7f...	Linus Torvalds	18 years
v2.6.23-rc5	commit 40ffbfad6b...	Linus Torvalds	18 years
v2.6.23-rc4	commit b07d68b5ca...	Linus Torvalds	18 years
v2.6.23-rc3	commit 39d3520c92...	Linus Torvalds	18 years
v2.6.23-rc2	commit d4ac2477fa...	Linus Torvalds	18 years
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generated by cgit v1.2.2 (git 2.25.0) at 2025-09-09 18:02:24 -0400

/*
 *  Generic process-grouping system.
 *
 *  Based originally on the cpuset system, extracted by Paul Menage
 *  Copyright (C) 2006 Google, Inc
 *
 *  Notifications support
 *  Copyright (C) 2009 Nokia Corporation
 *  Author: Kirill A. Shutemov
 *
 *  Copyright notices from the original cpuset code:
 *  --------------------------------------------------
 *  Copyright (C) 2003 BULL SA.
 *  Copyright (C) 2004-2006 Silicon Graphics, Inc.
 *
 *  Portions derived from Patrick Mochel's sysfs code.
 *  sysfs is Copyright (c) 2001-3 Patrick Mochel
 *
 *  2003-10-10 Written by Simon Derr.
 *  2003-10-22 Updates by Stephen Hemminger.
 *  2004 May-July Rework by Paul Jackson.
 *  ---------------------------------------------------
 *
 *  This file is subject to the terms and conditions of the GNU General Public
 *  License.  See the file COPYING in the main directory of the Linux
 *  distribution for more details.
 */

#include <linux/cgroup.h>
#include <linux/cred.h>
#include <linux/ctype.h>
#include <linux/errno.h>
#include <linux/init_task.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/mm.h>
#include <linux/mutex.h>
#include <linux/mount.h>
#include <linux/pagemap.h>
#include <linux/proc_fs.h>
#include <linux/rcupdate.h>
#include <linux/sched.h>
#include <linux/backing-dev.h>
#include <linux/seq_file.h>
#include <linux/slab.h>
#include <linux/magic.h>
#include <linux/spinlock.h>
#include <linux/string.h>
#include <linux/sort.h>
#include <linux/kmod.h>
#include <linux/module.h>
#include <linux/delayacct.h>
#include <linux/cgroupstats.h>
#include <linux/hashtable.h>
#include <linux/namei.h>
#include <linux/pid_namespace.h>
#include <linux/idr.h>
#include <linux/vmalloc.h> /* TODO: replace with more sophisticated array */
#include <linux/eventfd.h>
#include <linux/poll.h>
#include <linux/flex_array.h> /* used in cgroup_attach_task */
#include <linux/kthread.h>

#include <linux/atomic.h>

/*
 * cgroup_mutex is the master lock.  Any modification to cgroup or its
 * hierarchy must be performed while holding it.
 *
 * cgroup_root_mutex nests inside cgroup_mutex and should be held to modify
 * cgroupfs_root of any cgroup hierarchy - subsys list, flags,
 * release_agent_path and so on.  Modifying requires both cgroup_mutex and
 * cgroup_root_mutex.  Readers can acquire either of the two.  This is to
 * break the following locking order cycle.
 *
 *  A. cgroup_mutex -> cred_guard_mutex -> s_type->i_mutex_key -> namespace_sem
 *  B. namespace_sem -> cgroup_mutex
 *
 * B happens only through cgroup_show_options() and using cgroup_root_mutex
 * breaks it.
 */
#ifdef CONFIG_PROVE_RCU
DEFINE_MUTEX(cgroup_mutex);
EXPORT_SYMBOL_GPL(cgroup_mutex);	/* only for task_subsys_state_check() */
#else
static DEFINE_MUTEX(cgroup_mutex);
#endif

static DEFINE_MUTEX(cgroup_root_mutex);

/*
 * Generate an array of cgroup subsystem pointers. At boot time, this is
 * populated with the built in subsystems, and modular subsystems are
 * registered after that. The mutable section of this array is protected by
 * cgroup_mutex.
 */
#define SUBSYS(_x) [_x ## _subsys_id] = &_x ## _subsys,
#define IS_SUBSYS_ENABLED(option) IS_BUILTIN(option)
static struct cgroup_subsys *cgroup_subsys[CGROUP_SUBSYS_COUNT] = {
#include <linux/cgroup_subsys.h>
};

/*
 * The dummy hierarchy, reserved for the subsystems that are otherwise
 * unattached - it never has more than a single cgroup, and all tasks are
 * part of that cgroup.
 */
static struct cgroupfs_root cgroup_dummy_root;

/* dummy_top is a shorthand for the dummy hierarchy's top cgroup */
static struct cgroup * const cgroup_dummy_top = &cgroup_dummy_root.top_cgroup;

/*
 * cgroupfs file entry, pointed to from leaf dentry->d_fsdata.
 */
struct cfent {
	struct list_head		node;
	struct dentry			*dentry;
	struct cftype			*type;

	/* file xattrs */
	struct simple_xattrs		xattrs;
};

/*
 * CSS ID -- ID per subsys's Cgroup Subsys State(CSS). used only when
 * cgroup_subsys->use_id != 0.
 */
#define CSS_ID_MAX	(65535)
struct css_id {
	/*
	 * The css to which this ID points. This pointer is set to valid value
	 * after cgroup is populated. If cgroup is removed, this will be NULL.
	 * This pointer is expected to be RCU-safe because destroy()
	 * is called after synchronize_rcu(). But for safe use, css_tryget()
	 * should be used for avoiding race.
	 */
	struct cgroup_subsys_state __rcu *css;
	/*
	 * ID of this css.
	 */
	unsigned short id;
	/*
	 * Depth in hierarchy which this ID belongs to.
	 */
	unsigned short depth;
	/*
	 * ID is freed by RCU. (and lookup routine is RCU safe.)
	 */
	struct rcu_head rcu_head;
	/*
	 * Hierarchy of CSS ID belongs to.
	 */
	unsigned short stack[0]; /* Array of Length (depth+1) */
};

/*
 * cgroup_event represents events which userspace want to receive.
 */
struct cgroup_event {
	/*
	 * Cgroup which the event belongs to.
	 */
	struct cgroup *cgrp;
	/*
	 * Control file which the event associated.
	 */
	struct cftype *cft;
	/*
	 * eventfd to signal userspace about the event.
	 */
	struct eventfd_ctx *eventfd;
	/*
	 * Each of these stored in a list by the cgroup.
	 */
	struct list_head list;
	/*
	 * All fields below needed to unregister event when
	 * userspace closes eventfd.
	 */
	poll_table pt;
	wait_queue_head_t *wqh;
	wait_queue_t wait;
	struct work_struct remove;
};

/* The list of hierarchy roots */

static LIST_HEAD(cgroup_roots);
static int cgroup_root_count;

/*
 * Hierarchy ID allocation and mapping.  It follows the same exclusion
 * rules as other root ops - both cgroup_mutex and cgroup_root_mutex for
 * writes, either for reads.
 */
static DEFINE_IDR(cgroup_hierarchy_idr);

static struct cgroup_name root_cgroup_name = { .name = "/" };

/*
 * Assign a monotonically increasing serial number to cgroups.  It
 * guarantees cgroups with bigger numbers are newer than those with smaller
 * numbers.  Also, as cgroups are always appended to the parent's
 * ->children list, it guarantees that sibling cgroups are always sorted in
 * the ascending serial number order on the list.  Protected by
 * cgroup_mutex.
 */
static u64 cgroup_serial_nr_next = 1;

/* This flag indicates whether tasks in the fork and exit paths should
 * check for fork/exit handlers to call. This avoids us having to do
 * extra work in the fork/exit path if none of the subsystems need to
 * be called.
 */
static int need_forkexit_callback __read_mostly;

static void cgroup_offline_fn(struct work_struct *work);
static int cgroup_destroy_locked(struct cgroup *cgrp);
static int cgroup_addrm_files(struct cgroup *cgrp, struct cgroup_subsys *subsys,
			      struct cftype cfts[], bool is_add);

/* convenient tests for these bits */
static inline bool cgroup_is_dead(const struct cgroup *cgrp)
{
	return test_bit(CGRP_DEAD, &cgrp->flags);
}

/**
 * cgroup_is_descendant - test ancestry
 * @cgrp: the cgroup to be tested
 * @ancestor: possible ancestor of @cgrp
 *
 * Test whether @cgrp is a descendant of @ancestor.  It also returns %true
 * if @cgrp == @ancestor.  This function is safe to call as long as @cgrp
 * and @ancestor are accessible.
 */
bool cgroup_is_descendant(struct cgroup *cgrp, struct cgroup *ancestor)
{
	while (cgrp) {
		if (cgrp == ancestor)
			return true;
		cgrp = cgrp->parent;
	}
	return false;
}
EXPORT_SYMBOL_GPL(cgroup_is_descendant);

static int cgroup_is_releasable(const struct cgroup *cgrp)
{
	const int bits =
		(1 << CGRP_RELEASABLE) |
		(1 << CGRP_NOTIFY_ON_RELEASE);
	return (cgrp->flags & bits) == bits;
}

static int notify_on_release(const struct cgroup *cgrp)
{
	return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
}

/**
 * for_each_subsys - iterate all loaded cgroup subsystems
 * @ss: the iteration cursor
 * @i: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
 *
 * Should be called under cgroup_mutex.
 */
#define for_each_subsys(ss, i)						\
	for ((i) = 0; (i) < CGROUP_SUBSYS_COUNT; (i)++)			\
		if (({ lockdep_assert_held(&cgroup_mutex);		\
		       !((ss) = cgroup_subsys[i]); })) { }		\
		else

/**
 * for_each_builtin_subsys - iterate all built-in cgroup subsystems
 * @ss: the iteration cursor
 * @i: the index of @ss, CGROUP_BUILTIN_SUBSYS_COUNT after reaching the end
 *
 * Bulit-in subsystems are always present and iteration itself doesn't
 * require any synchronization.
 */
#define for_each_builtin_subsys(ss, i)					\
	for ((i) = 0; (i) < CGROUP_BUILTIN_SUBSYS_COUNT &&		\
	     (((ss) = cgroup_subsys[i]) || true); (i)++)

/* iterate each subsystem attached to a hierarchy */
#define for_each_root_subsys(root, ss)					\
	list_for_each_entry((ss), &(root)->subsys_list, sibling)

/* iterate across the active hierarchies */
#define for_each_active_root(root)					\
	list_for_each_entry((root), &cgroup_roots, root_list)

static inline struct cgroup *__d_cgrp(struct dentry *dentry)
{
	return dentry->d_fsdata;
}

static inline struct cfent *__d_cfe(struct dentry *dentry)
{
	return dentry->d_fsdata;
}

static inline struct cftype *__d_cft(struct dentry *dentry)
{
	return __d_cfe(dentry)->type;
}

/**
 * cgroup_lock_live_group - take cgroup_mutex and check that cgrp is alive.
 * @cgrp: the cgroup to be checked for liveness
 *
 * On success, returns true; the mutex should be later unlocked.  On
 * failure returns false with no lock held.
 */
static bool cgroup_lock_live_group(struct cgroup *cgrp)
{
	mutex_lock(&cgroup_mutex);
	if (cgroup_is_dead(cgrp)) {
		mutex_unlock(&cgroup_mutex);
		return false;
	}
	return true;
}

/* the list of cgroups eligible for automatic release. Protected by
 * release_list_lock */
static LIST_HEAD(release_list);
static DEFINE_RAW_SPINLOCK(release_list_lock);
static void cgroup_release_agent(struct work_struct *work);
static DECLARE_WORK(release_agent_work, cgroup_release_agent);
static void check_for_release(struct cgroup *cgrp);

/*
 * A cgroup can be associated with multiple css_sets as different tasks may
 * belong to different cgroups on different hierarchies.  In the other
 * direction, a css_set is naturally associated with multiple cgroups.
 * This M:N relationship is represented by the following link structure
 * which exists for each association and allows traversing the associations
 * from both sides.
 */
struct cgrp_cset_link {
	/* the cgroup and css_set this link associates */
	struct cgroup		*cgrp;
	struct css_set		*cset;

	/* list of cgrp_cset_links anchored at cgrp->cset_links */
	struct list_head	cset_link;

	/* list of cgrp_cset_links anchored at css_set->cgrp_links */
	struct list_head	cgrp_link;
};

/* The default css_set - used by init and its children prior to any
 * hierarchies being mounted. It contains a pointer to the root state
 * for each subsystem. Also used to anchor the list of css_sets. Not
 * reference-counted, to improve performance when child cgroups
 * haven't been created.
 */

static struct css_set init_css_set;
static struct cgrp_cset_link init_cgrp_cset_link;

static int cgroup_init_idr(struct cgroup_subsys *ss,
			   struct cgroup_subsys_state *css);

/* css_set_lock protects the list of css_set objects, and the
 * chain of tasks off each css_set.  Nests outside task->alloc_lock
 * due to cgroup_iter_start() */
static DEFINE_RWLOCK(css_set_lock);
static int css_set_count;

/*
 * hash table for cgroup groups. This improves the performance to find
 * an existing css_set. This hash doesn't (currently) take into
 * account cgroups in empty hierarchies.
 */
#define CSS_SET_HASH_BITS	7
static DEFINE_HASHTABLE(css_set_table, CSS_SET_HASH_BITS);

static unsigned long css_set_hash(struct cgroup_subsys_state *css[])
{
	unsigned long key = 0UL;
	struct cgroup_subsys *ss;
	int i;

	for_each_subsys(ss, i)
		key += (unsigned long)css[i];
	key = (key >> 16) ^ key;

	return key;
}

/* We don't maintain the lists running through each css_set to its
 * task until after the first call to cgroup_iter_start(). This
 * reduces the fork()/exit() overhead for people who have cgroups
 * compiled into their kernel but not actually in use */
static int use_task_css_set_links __read_mostly;

static void __put_css_set(struct css_set *cset, int taskexit)
{
	struct cgrp_cset_link *link, *tmp_link;

	/*
	 * Ensure that the refcount doesn't hit zero while any readers
	 * can see it. Similar to atomic_dec_and_lock(), but for an
	 * rwlock
	 */
	if (atomic_add_unless(&cset->refcount, -1, 1))
		return;
	write_lock(&css_set_lock);
	if (!atomic_dec_and_test(&cset->refcount)) {
		write_unlock(&css_set_lock);
		return;
	}

	/* This css_set is dead. unlink it and release cgroup refcounts */
	hash_del(&cset->hlist);
	css_set_count--;

	list_for_each_entry_safe(link, tmp_link, &cset->cgrp_links, cgrp_link) {
		struct cgroup *cgrp = link->cgrp;

		list_del(&link->cset_link);
		list_del(&link->cgrp_link);

		/* @cgrp can't go away while we're holding css_set_lock */
		if (list_empty(&cgrp->cset_links) && notify_on_release(cgrp)) {
			if (taskexit)
				set_bit(CGRP_RELEASABLE, &cgrp->flags);
			check_for_release(cgrp);
		}

		kfree(link);
	}

	write_unlock(&css_set_lock);
	kfree_rcu(cset, rcu_head);
}

/*
 * refcounted get/put for css_set objects
 */
static inline void get_css_set(struct css_set *cset)
{
	atomic_inc(&cset->refcount);
}

static inline void put_css_set(struct css_set *cset)
{
	__put_css_set(cset, 0);
}

static inline void put_css_set_taskexit(struct css_set *cset)
{
	__put_css_set(cset, 1);
}

/**
 * compare_css_sets - helper function for find_existing_css_set().
 * @cset: candidate css_set being tested
 * @old_cset: existing css_set for a task
 * @new_cgrp: cgroup that's being entered by the task
 * @template: desired set of css pointers in css_set (pre-calculated)
 *
 * Returns true if "cg" matches "old_cg" except for the hierarchy
 * which "new_cgrp" belongs to, for which it should match "new_cgrp".
 */
static bool compare_css_sets(struct css_set *cset,
			     struct css_set *old_cset,
			     struct cgroup *new_cgrp,
			     struct cgroup_subsys_state *template[])
{
	struct list_head *l1, *l2;

	if (memcmp(template, cset->subsys, sizeof(cset->subsys))) {
		/* Not all subsystems matched */
		return false;
	}

	/*
	 * Compare cgroup pointers in order to distinguish between
	 * different cgroups in heirarchies with no subsystems. We
	 * could get by with just this check alone (and skip the
	 * memcmp above) but on most setups the memcmp check will
	 * avoid the need for this more expensive check on almost all
	 * candidates.
	 */

	l1 = &cset->cgrp_links;
	l2 = &old_cset->cgrp_links;
	while (1) {
		struct cgrp_cset_link *link1, *link2;
		struct cgroup *cgrp1, *cgrp2;

		l1 = l1->next;
		l2 = l2->next;
		/* See if we reached the end - both lists are equal length. */
		if (l1 == &cset->cgrp_links) {
			BUG_ON(l2 != &old_cset->cgrp_links);
			break;
		} else {
			BUG_ON(l2 == &old_cset->cgrp_links);
		}
		/* Locate the cgroups associated with these links. */
		link1 = list_entry(l1, struct cgrp_cset_link, cgrp_link);
		link2 = list_entry(l2, struct cgrp_cset_link, cgrp_link);
		cgrp1 = link1->cgrp;
		cgrp2 = link2->cgrp;
		/* Hierarchies should be linked in the same order. */
		BUG_ON(cgrp1->root != cgrp2->root);

		/*
		 * If this hierarchy is the hierarchy of the cgroup
		 * that's changing, then we need to check that this
		 * css_set points to the new cgroup; if it's any other
		 * hierarchy, then this css_set should point to the
		 * same cgroup as the old css_set.
		 */
		if (cgrp1->root == new_cgrp->root) {
			if (cgrp1 != new_cgrp)
				return false;
		} else {
			if (cgrp1 != cgrp2)
				return false;
		}
	}
	return true;
}

/**
 * find_existing_css_set - init css array and find the matching css_set
 * @old_cset: the css_set that we're using before the cgroup transition
 * @cgrp: the cgroup that we're moving into
 * @template: out param for the new set of csses, should be clear on entry
 */
static struct css_set *find_existing_css_set(struct css_set *old_cset,
					struct cgroup *cgrp,
					struct cgroup_subsys_state *template[])
{
	struct cgroupfs_root *root = cgrp->root;
	struct cgroup_subsys *ss;
	struct css_set *cset;
	unsigned long key;
	int i;

	/*
	 * Build the set of subsystem state objects that we want to see in the
	 * new css_set. while subsystems can change globally, the entries here
	 * won't change, so no need for locking.
	 */
	for_each_subsys(ss, i) {
		if (root->subsys_mask & (1UL << i)) {
			/* Subsystem is in this hierarchy. So we want
			 * the subsystem state from the new
			 * cgroup */
			template[i] = cgrp->subsys[i];
		} else {
			/* Subsystem is not in this hierarchy, so we
			 * don't want to change the subsystem state */
			template[i] = old_cset->subsys[i];
		}
	}

	key = css_set_hash(template);
	hash_for_each_possible(css_set_table, cset, hlist, key) {
		if (!compare_css_sets(cset, old_cset, cgrp, template))
			continue;

		/* This css_set matches what we need */
		return cset;
	}

	/* No existing cgroup group matched */
	return NULL;
}

static void free_cgrp_cset_links(struct list_head *links_to_free)
{
	struct cgrp_cset_link *link, *tmp_link;

	list_for_each_entry_safe(link, tmp_link, links_to_free, cset_link) {
		list_del(&link->cset_link);
		kfree(link);
	}
}

/**
 * allocate_cgrp_cset_links - allocate cgrp_cset_links
 * @count: the number of links to allocate
 * @tmp_links: list_head the allocated links are put on
 *
 * Allocate @count cgrp_cset_link structures and chain them on @tmp_links
 * through ->cset_link.  Returns 0 on success or -errno.
 */
static int allocate_cgrp_cset_links(int count, struct list_head *tmp_links)
{
	struct cgrp_cset_link *link;
	int i;

	INIT_LIST_HEAD(tmp_links);

	for (i = 0; i < count; i++) {
		link = kzalloc(sizeof(*link), GFP_KERNEL);
		if (!link) {
			free_cgrp_cset_links(tmp_links);
			return -ENOMEM;
		}
		list_add(&link->cset_link, tmp_links);
	}
	return 0;
}

/**
 * link_css_set - a helper function to link a css_set to a cgroup
 * @tmp_links: cgrp_cset_link objects allocated by allocate_cgrp_cset_links()
 * @cset: the css_set to be linked
 * @cgrp: the destination cgroup
 */
static void link_css_set(struct list_head *tmp_links, struct css_set *cset,
			 struct cgroup *cgrp)
{
	struct cgrp_cset_link *link;

	BUG_ON(list_empty(tmp_links));
	link = list_first_entry(tmp_links, struct cgrp_cset_link, cset_link);
	link->cset = cset;
	link->cgrp = cgrp;
	list_move(&link->cset_link, &cgrp->cset_links);
	/*
	 * Always add links to the tail of the list so that the list
	 * is sorted by order of hierarchy creation
	 */
	list_add_tail(&link->cgrp_link, &cset->cgrp_links);
}

/**
 * find_css_set - return a new css_set with one cgroup updated
 * @old_cset: the baseline css_set
 * @cgrp: the cgroup to be updated
 *
 * Return a new css_set that's equivalent to @old_cset, but with @cgrp
 * substituted into the appropriate hierarchy.
 */
static struct css_set *find_css_set(struct css_set *old_cset,
				    struct cgroup *cgrp)
{
	struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT] = { };
	struct css_set *cset;
	struct list_head tmp_links;
	struct cgrp_cset_link *link;
	unsigned long key;

	lockdep_assert_held(&cgroup_mutex);

	/* First see if we already have a cgroup group that matches
	 * the desired set */
	read_lock(&css_set_lock);
	cset = find_existing_css_set(old_cset, cgrp, template);
	if (cset)
		get_css_set(cset);
	read_unlock(&css_set_lock);

	if (cset)
		return cset;

	cset = kzalloc(sizeof(*cset), GFP_KERNEL);
	if (!cset)
		return NULL;

	/* Allocate all the cgrp_cset_link objects that we'll need */
	if (allocate_cgrp_cset_links(cgroup_root_count, &tmp_links) < 0) {
		kfree(cset);
		return NULL;
	}

	atomic_set(&cset->refcount, 1);
	INIT_LIST_HEAD(&cset->cgrp_links);
	INIT_LIST_HEAD(&cset->tasks);
	INIT_HLIST_NODE(&cset->hlist);

	/* Copy the set of subsystem state objects generated in
	 * find_existing_css_set() */
	memcpy(cset->subsys, template, sizeof(cset->subsys));

	write_lock(&css_set_lock);
	/* Add reference counts and links from the new css_set. */
	list_for_each_entry(link, &old_cset->cgrp_links, cgrp_link) {
		struct cgroup *c = link->cgrp;

		if (c->root == cgrp->root)
			c = cgrp;
		link_css_set(&tmp_links, cset, c);
	}

	BUG_ON(!list_empty(&tmp_links));

	css_set_count++;

	/* Add this cgroup group to the hash table */
	key = css_set_hash(cset->subsys);
	hash_add(css_set_table, &cset->hlist, key);

	write_unlock(&css_set_lock);

	return cset;
}

/*
 * Return the cgroup for "task" from the given hierarchy. Must be
 * called with cgroup_mutex held.
 */
static struct cgroup *task_cgroup_from_root(struct task_struct *task,
					    struct cgroupfs_root *root)
{
	struct css_set *cset;
	struct cgroup *res = NULL;

	BUG_ON(!mutex_is_locked(&cgroup_mutex));
	read_lock(&css_set_lock);
	/*
	 * No need to lock the task - since we hold cgroup_mutex the
	 * task can't change groups, so the only thing that can happen
	 * is that it exits and its css is set back to init_css_set.
	 */
	cset = task_css_set(task);
	if (cset == &init_css_set) {
		res = &root->top_cgroup;
	} else {
		struct cgrp_cset_link *link;

		list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
			struct cgroup *c = link->cgrp;

			if (c->root == root) {
				res = c;
				break;
			}
		}
	}
	read_unlock(&css_set_lock);
	BUG_ON(!res);
	return res;
}

/*
 * There is one global cgroup mutex. We also require taking
 * task_lock() when dereferencing a task's cgroup subsys pointers.
 * See "The task_lock() exception", at the end of this comment.
 *
 * A task must hold cgroup_mutex to modify cgroups.
 *
 * Any task can increment and decrement the count field without lock.
 * So in general, code holding cgroup_mutex can't rely on the count
 * field not changing.  However, if the count goes to zero, then only
 * cgroup_attach_task() can increment it again.  Because a count of zero
 * means that no tasks are currently attached, therefore there is no
 * way a task attached to that cgroup can fork (the other way to
 * increment the count).  So code holding cgroup_mutex can safely
 * assume that if the count is zero, it will stay zero. Similarly, if
 * a task holds cgroup_mutex on a cgroup with zero count, it
 * knows that the cgroup won't be removed, as cgroup_rmdir()
 * needs that mutex.
 *
 * The fork and exit callbacks cgroup_fork() and cgroup_exit(), don't
 * (usually) take cgroup_mutex.  These are the two most performance
 * critical pieces of code here.  The exception occurs on cgroup_exit(),
 * when a task in a notify_on_release cgroup exits.  Then cgroup_mutex
 * is taken, and if the cgroup count is zero, a usermode call made
 * to the release agent with the name of the cgroup (path relative to
 * the root of cgroup file system) as the argument.
 *
 * A cgroup can only be deleted if both its 'count' of using tasks
 * is zero, and its list of 'children' cgroups is empty.  Since all
 * tasks in the system use _some_ cgroup, and since there is always at
 * least one task in the system (init, pid == 1), therefore, top_cgroup
 * always has either children cgroups and/or using tasks.  So we don't
 * need a special hack to ensure that top_cgroup cannot be deleted.
 *
 *	The task_lock() exception
 *
 * The need for this exception arises from the action of
 * cgroup_attach_task(), which overwrites one task's cgroup pointer with
 * another.  It does so using cgroup_mutex, however there are
 * several performance critical places that need to reference
 * task->cgroup without the expense of grabbing a system global
 * mutex.  Therefore except as noted below, when dereferencing or, as
 * in cgroup_attach_task(), modifying a task's cgroup pointer we use
 * task_lock(), which acts on a spinlock (task->alloc_lock) already in
 * the task_struct routinely used for such matters.
 *
 * P.S.  One more locking exception.  RCU is used to guard the
 * update of a tasks cgroup pointer by cgroup_attach_task()
 */

/*
 * A couple of forward declarations required, due to cyclic reference loop:
 * cgroup_mkdir -> cgroup_create -> cgroup_populate_dir ->
 * cgroup_add_file -> cgroup_create_file -> cgroup_dir_inode_operations
 * -> cgroup_mkdir.
 */

static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode);
static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry);
static int cgroup_populate_dir(struct cgroup *cgrp, bool base_files,
			       unsigned long subsys_mask);
static const struct inode_operations cgroup_dir_inode_operations;
static const struct file_operations proc_cgroupstats_operations;

static struct backing_dev_info cgroup_backing_dev_info = {
	.name		= "cgroup",
	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK,
};

static int alloc_css_id(struct cgroup_subsys *ss,
			struct cgroup *parent, struct cgroup *child);

static struct inode *cgroup_new_inode(umode_t mode, struct super_block *sb)
{
	struct inode *inode = new_inode(sb);

	if (inode) {
		inode->i_ino = get_next_ino();
		inode->i_mode = mode;
		inode->i_uid = current_fsuid();
		inode->i_gid = current_fsgid();
		inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
		inode->i_mapping->backing_dev_info = &cgroup_backing_dev_info;
	}
	return inode;
}

static struct cgroup_name *cgroup_alloc_name(struct dentry *dentry)
{
	struct cgroup_name *name;

	name = kmalloc(sizeof(*name) + dentry->d_name.len + 1, GFP_KERNEL);
	if (!name)
		return NULL;
	strcpy(name->name, dentry->d_name.name);
	return name;
}

static void cgroup_free_fn(struct work_struct *work)
{
	struct cgroup *cgrp = container_of(work, struct cgroup, destroy_work);
	struct cgroup_subsys *ss;

	mutex_lock(&cgroup_mutex);
	/*
	 * Release the subsystem state objects.
	 */
	for_each_root_subsys(cgrp->root, ss)
		ss->css_free(cgrp);

	cgrp->root->number_of_cgroups--;
	mutex_unlock(&cgroup_mutex);

	/*
	 * We get a ref to the parent's dentry, and put the ref when
	 * this cgroup is being freed, so it's guaranteed that the
	 * parent won't be destroyed before its children.
	 */
	dput(cgrp->parent->dentry);

	ida_simple_remove(&cgrp->root->cgroup_ida, cgrp->id);

	/*
	 * Drop the active superblock reference that we took when we
	 * created the cgroup. This will free cgrp->root, if we are
	 * holding the last reference to @sb.
	 */
	deactivate_super(cgrp->root->sb);

	/*
	 * if we're getting rid of the cgroup, refcount should ensure
	 * that there are no pidlists left.
	 */
	BUG_ON(!list_empty(&cgrp->pidlists));

	simple_xattrs_free(&cgrp->xattrs);

	kfree(rcu_dereference_raw(cgrp->name));
	kfree(cgrp);
}

static void cgroup_free_rcu(struct rcu_head *head)
{
	struct cgroup *cgrp = container_of(head, struct cgroup, rcu_head);

	INIT_WORK(&cgrp->destroy_work, cgroup_free_fn);
	schedule_work(&cgrp->destroy_work);
}

static void cgroup_diput(struct dentry *dentry, struct inode *inode)
{
	/* is dentry a directory ? if so, kfree() associated cgroup */
	if (S_ISDIR(inode->i_mode)) {
		struct cgroup *cgrp = dentry->d_fsdata;

		BUG_ON(!(cgroup_is_dead(cgrp)));
		call_rcu(&cgrp->rcu_head, cgroup_free_rcu);
	} else {
		struct cfent *cfe = __d_cfe(dentry);
		struct cgroup *cgrp = dentry->d_parent->d_fsdata;

		WARN_ONCE(!list_empty(&cfe->node) &&
			  cgrp != &cgrp->root->top_cgroup,
			  "cfe still linked for %s\n", cfe->type->name);
		simple_xattrs_free(&cfe->xattrs);
		kfree(cfe);
	}
	iput(inode);
}

static int cgroup_delete(const struct dentry *d)
{
	return 1;
}

static void remove_dir(struct dentry *d)
{
	struct dentry *parent = dget(d->d_parent);

	d_delete(d);
	simple_rmdir(parent->d_inode, d);
	dput(parent);
}

static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
{
	struct cfent *cfe;

	lockdep_assert_held(&cgrp->dentry->d_inode->i_mutex);
	lockdep_assert_held(&cgroup_mutex);

	/*
	 * If we're doing cleanup due to failure of cgroup_create(),
	 * the corresponding @cfe may not exist.
	 */
	list_for_each_entry(cfe, &cgrp->files, node) {
		struct dentry *d = cfe->dentry;

		if (cft && cfe->type != cft)
			continue;

		dget(d);
		d_delete(d);
		simple_unlink(cgrp->dentry->d_inode, d);
		list_del_init(&cfe->node);
		dput(d);

		break;
	}
}

/**
 * cgroup_clear_directory - selective removal of base and subsystem files
 * @dir: directory containing the files
 * @base_files: true if the base files should be removed
 * @subsys_mask: mask of the subsystem ids whose files should be removed
 */
static void cgroup_clear_directory(struct dentry *dir, bool base_files,
				   unsigned long subsys_mask)
{
	struct cgroup *cgrp = __d_cgrp(dir);
	struct cgroup_subsys *ss;

	for_each_root_subsys(cgrp->root, ss) {
		struct cftype_set *set;
		if (!test_bit(ss->subsys_id, &subsys_mask))
			continue;
		list_for_each_entry(set, &ss->cftsets, node)
			cgroup_addrm_files(cgrp, NULL, set->cfts, false);
	}
	if (base_files) {
		while (!list_empty(&cgrp->files))
			cgroup_rm_file(cgrp, NULL);
	}
}

/*
 * NOTE : the dentry must have been dget()'ed
 */
static void cgroup_d_remove_dir(struct dentry *dentry)
{
	struct dentry *parent;
	struct cgroupfs_root *root = dentry->d_sb->s_fs_info;

	cgroup_clear_directory(dentry, true, root->subsys_mask);

	parent = dentry->d_parent;
	spin_lock(&parent->d_lock);
	spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
	list_del_init(&dentry->d_u.d_child);
	spin_unlock(&dentry->d_lock);
	spin_unlock(&parent->d_lock);
	remove_dir(dentry);
}

/*
 * Call with cgroup_mutex held. Drops reference counts on modules, including
 * any duplicate ones that parse_cgroupfs_options took. If this function
 * returns an error, no reference counts are touched.
 */
static int rebind_subsystems(struct cgroupfs_root *root,
			     unsigned long added_mask, unsigned removed_mask)
{
	struct cgroup *cgrp = &root->top_cgroup;
	struct cgroup_subsys *ss;
	int i;

	BUG_ON(!mutex_is_locked(&cgroup_mutex));
	BUG_ON(!mutex_is_locked(&cgroup_root_mutex));

	/* Check that any added subsystems are currently free */
	for_each_subsys(ss, i) {
		unsigned long bit = 1UL << i;

		if (!(bit & added_mask))
			continue;

		if (ss->root != &cgroup_dummy_root) {
			/* Subsystem isn't free */
			return -EBUSY;
		}
	}

	/* Currently we don't handle adding/removing subsystems when
	 * any child cgroups exist. This is theoretically supportable
	 * but involves complex error handling, so it's being left until
	 * later */
	if (root->number_of_cgroups > 1)
		return -EBUSY;

	/* Process each subsystem */
	for_each_subsys(ss, i) {
		unsigned long bit = 1UL << i;

		if (bit & added_mask) {
			/* We're binding this subsystem to this hierarchy */
			BUG_ON(cgrp->subsys[i]);
			BUG_ON(!cgroup_dummy_top->subsys[i]);
			BUG_ON(cgroup_dummy_top->subsys[i]->cgroup != cgroup_dummy_top);

			cgrp->subsys[i] = cgroup_dummy_top->subsys[i];
			cgrp->subsys[i]->cgroup = cgrp;
			list_move(&ss->sibling, &root->subsys_list);
			ss->root = root;
			if (ss->bind)
				ss->bind(cgrp);

			/* refcount was already taken, and we're keeping it */
			root->subsys_mask |= bit;
		} else if (bit & removed_mask) {
			/* We're removing this subsystem */
			BUG_ON(cgrp->subsys[i] != cgroup_dummy_top->subsys[i]);
			BUG_ON(cgrp->subsys[i]->cgroup != cgrp);

			if (ss->bind)
				ss->bind(cgroup_dummy_top);
			cgroup_dummy_top->subsys[i]->cgroup = cgroup_dummy_top;
			cgrp->subsys[i] = NULL;
			cgroup_subsys[i]->root = &cgroup_dummy_root;
			list_move(&ss->sibling, &cgroup_dummy_root.subsys_list);

			/* subsystem is now free - drop reference on module */
			module_put(ss->module);
			root->subsys_mask &= ~bit;
		} else if (bit & root->subsys_mask) {
			/* Subsystem state should already exist */
			BUG_ON(!cgrp->subsys[i]);
			/*
			 * a refcount was taken, but we already had one, so
			 * drop the extra reference.
			 */
			module_put(ss->module);
#ifdef CONFIG_MODULE_UNLOAD
			BUG_ON(ss->module && !module_refcount(ss->module));
#endif
		} else {
			/* Subsystem state shouldn't exist */
			BUG_ON(cgrp->subsys[i]);
		}
	}

	/*
	 * Mark @root has finished binding subsystems.  @root->subsys_mask
	 * now matches the bound subsystems.
	 */
	root->flags |= CGRP_ROOT_SUBSYS_BOUND;

	return 0;
}

static int cgroup_show_options(struct seq_file *seq, struct dentry *dentry)
{
	struct cgroupfs_root *root = dentry->d_sb->s_fs_info;
	struct cgroup_subsys *ss;

	mutex_lock(&cgroup_root_mutex);
	for_each_root_subsys(root, ss)
		seq_printf(seq, ",%s", ss->name);
	if (root->flags & CGRP_ROOT_SANE_BEHAVIOR)
		seq_puts(seq, ",sane_behavior");
	if (root->flags & CGRP_ROOT_NOPREFIX)
		seq_puts(seq, ",noprefix");
	if (root->flags & CGRP_ROOT_XATTR)
		seq_puts(seq, ",xattr");
	if (strlen(root->release_agent_path))
		seq_printf(seq, ",release_agent=%s", root->release_agent_path);
	if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->top_cgroup.flags))
		seq_puts(seq, ",clone_children");
	if (strlen(root->name))
		seq_printf(seq, ",name=%s", root->name);
	mutex_unlock(&cgroup_root_mutex);
	return 0;
}

struct cgroup_sb_opts {
	unsigned long subsys_mask;
	unsigned long flags;
	char *release_agent;
	bool cpuset_clone_children;
	char *name;
	/* User explicitly requested empty subsystem */
	bool none;

	struct cgroupfs_root *new_root;

};

/*
 * Convert a hierarchy specifier into a bitmask of subsystems and
 * flags. Call with cgroup_mutex held to protect the cgroup_subsys[]
 * array. This function takes refcounts on subsystems to be used, unless it
 * returns error, in which case no refcounts are taken.
 */
static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
{
	char *token, *o = data;
	bool all_ss = false, one_ss = false;
	unsigned long mask = (unsigned long)-1;
	bool module_pin_failed = false;
	struct cgroup_subsys *ss;
	int i;

	BUG_ON(!mutex_is_locked(&cgroup_mutex));

#ifdef CONFIG_CPUSETS
	mask = ~(1UL << cpuset_subsys_id);
#endif

	memset(opts, 0, sizeof(*opts));

	while ((token = strsep(&o, ",")) != NULL) {
		if (!*token)
			return -EINVAL;
		if (!strcmp(token, "none")) {
			/* Explicitly have no subsystems */
			opts->none = true;
			continue;
		}
		if (!strcmp(token, "all")) {
			/* Mutually exclusive option 'all' + subsystem name */
			if (one_ss)
				return -EINVAL;
			all_ss = true;
			continue;
		}
		if (!strcmp(token, "__DEVEL__sane_behavior")) {
			opts->flags |= CGRP_ROOT_SANE_BEHAVIOR;
			continue;
		}
		if (!strcmp(token, "noprefix")) {
			opts->flags |= CGRP_ROOT_NOPREFIX;
			continue;
		}
		if (!strcmp(token, "clone_children")) {
			opts->cpuset_clone_children = true;
			continue;
		}
		if (!strcmp(token, "xattr")) {
			opts->flags |= CGRP_ROOT_XATTR;
			continue;
		}
		if (!strncmp(token, "release_agent=", 14)) {
			/* Specifying two release agents is forbidden */
			if (opts->release_agent)
				return -EINVAL;
			opts->release_agent =
				kstrndup(token + 14, PATH_MAX - 1, GFP_KERNEL);
			if (!opts->release_agent)
				return -ENOMEM;
			continue;
		}
		if (!strncmp(token, "name=", 5)) {
			const char *name = token + 5;
			/* Can't specify an empty name */
			if (!strlen(name))
				return -EINVAL;
			/* Must match [\w.-]+ */
			for (i = 0; i < strlen(name); i++) {
				char c = name[i];
				if (isalnum(c))
					continue;
				if ((c == '.') || (c == '-') || (c == '_'))
					continue;
				return -EINVAL;
			}
			/* Specifying two names is forbidden */
			if (opts->name)
				return -EINVAL;
			opts->name = kstrndup(name,
					      MAX_CGROUP_ROOT_NAMELEN - 1,
					      GFP_KERNEL);
			if (!opts->name)
				return -ENOMEM;

			continue;
		}

		for_each_subsys(ss, i) {
			if (strcmp(token, ss->name))
				continue;
			if (ss->disabled)
				continue;

			/* Mutually exclusive option 'all' + subsystem name */
			if (all_ss)
				return -EINVAL;
			set_bit(i, &opts->subsys_mask);
			one_ss = true;

			break;
		}
		if (i == CGROUP_SUBSYS_COUNT)
			return -ENOENT;
	}

	/*
	 * If the 'all' option was specified select all the subsystems,
	 * otherwise if 'none', 'name=' and a subsystem name options
	 * were not specified, let's default to 'all'
	 */
	if (all_ss || (!one_ss && !opts->none && !opts->name))
		for_each_subsys(ss, i)
			if (!ss->disabled)
				set_bit(i, &opts->subsys_mask);

	/* Consistency checks */

	if (opts->flags & CGRP_ROOT_SANE_BEHAVIOR) {
		pr_warning("cgroup: sane_behavior: this is still under development and its behaviors will change, proceed at your own risk\n");

		if (opts->flags & CGRP_ROOT_NOPREFIX) {
			pr_err("cgroup: sane_behavior: noprefix is not allowed\n");
			return -EINVAL;
		}

		if (opts->cpuset_clone_children) {
			pr_err("cgroup: sane_behavior: clone_children is not allowed\n");
			return -EINVAL;
		}
	}

	/*
	 * Option noprefix was introduced just for backward compatibility
	 * with the old cpuset, so we allow noprefix only if mounting just
	 * the cpuset subsystem.
	 */
	if ((opts->flags & CGRP_ROOT_NOPREFIX) && (opts->subsys_mask & mask))
		return -EINVAL;


	/* Can't specify "none" and some subsystems */
	if (opts->subsys_mask && opts->none)
		return -EINVAL;

	/*
	 * We either have to specify by name or by subsystems. (So all
	 * empty hierarchies must have a name).
	 */
	if (!opts->subsys_mask && !opts->name)
		return -EINVAL;

	/*
	 * Grab references on all the modules we'll need, so the subsystems
	 * don't dance around before rebind_subsystems attaches them. This may
	 * take duplicate reference counts on a subsystem that's already used,
	 * but rebind_subsystems handles this case.
	 */
	for_each_subsys(ss, i) {
		if (!(opts->subsys_mask & (1UL << i)))
			continue;
		if (!try_module_get(cgroup_subsys[i]->module)) {
			module_pin_failed = true;
			break;
		}
	}
	if (module_pin_failed) {
		/*
		 * oops, one of the modules was going away. this means that we
		 * raced with a module_delete call, and to the user this is
		 * essentially a "subsystem doesn't exist" case.
		 */
		for (i--; i >= 0; i--) {
			/* drop refcounts only on the ones we took */
			unsigned long bit = 1UL << i;

			if (!(bit & opts->subsys_mask))
				continue;
			module_put(cgroup_subsys[i]->module);
		}
		return -ENOENT;
	}

	return 0;
}

static void drop_parsed_module_refcounts(unsigned long subsys_mask)
{
	struct cgroup_subsys *ss;
	int i;

	mutex_lock(&cgroup_mutex);
	for_each_subsys(ss, i)
		if (subsys_mask & (1UL << i))
			module_put(cgroup_subsys[i]->module);
	mutex_unlock(&cgroup_mutex);
}

static int cgroup_remount(struct super_block *sb, int *flags, char *data)
{
	int ret = 0;
	struct cgroupfs_root *root = sb->s_fs_info;
	struct cgroup *cgrp = &root->top_cgroup;
	struct cgroup_sb_opts opts;
	unsigned long added_mask, removed_mask;

	if (root->flags & CGRP_ROOT_SANE_BEHAVIOR) {
		pr_err("cgroup: sane_behavior: remount is not allowed\n");
		return -EINVAL;
	}

	mutex_lock(&cgrp->dentry->d_inode->i_mutex);
	mutex_lock(&cgroup_mutex);
	mutex_lock(&cgroup_root_mutex);

	/* See what subsystems are wanted */
	ret = parse_cgroupfs_options(data, &opts);
	if (ret)
		goto out_unlock;

	if (opts.subsys_mask != root->subsys_mask || opts.release_agent)
		pr_warning("cgroup: option changes via remount are deprecated (pid=%d comm=%s)\n",
			   task_tgid_nr(current), current->comm);

	added_mask = opts.subsys_mask & ~root->subsys_mask;
	removed_mask = root->subsys_mask & ~opts.subsys_mask;

	/* Don't allow flags or name to change at remount */
	if (((opts.flags ^ root->flags) & CGRP_ROOT_OPTION_MASK) ||
	    (opts.name && strcmp(opts.name, root->name))) {
		pr_err("cgroup: option or name mismatch, new: 0x%lx \"%s\", old: 0x%lx \"%s\"\n",
		       opts.flags & CGRP_ROOT_OPTION_MASK, opts.name ?: "",
		       root->flags & CGRP_ROOT_OPTION_MASK, root->name);
		ret = -EINVAL;
		goto out_unlock;
	}

	/*
	 * Clear out the files of subsystems that should be removed, do
	 * this before rebind_subsystems, since rebind_subsystems may
	 * change this hierarchy's subsys_list.
	 */
	cgroup_clear_directory(cgrp->dentry, false, removed_mask);

	ret = rebind_subsystems(root, added_mask, removed_mask);
	if (ret) {
		/* rebind_subsystems failed, re-populate the removed files */
		cgroup_populate_dir(cgrp, false, removed_mask);
		goto out_unlock;
	}

	/* re-populate subsystem files */
	cgroup_populate_dir(cgrp, false, added_mask);

	if (opts.release_agent)
		strcpy(root->release_agent_path, opts.release_agent);
 out_unlock:
	kfree(opts.release_agent);
	kfree(opts.name);
	mutex_unlock(&cgroup_root_mutex);
	mutex_unlock(&cgroup_mutex);
	mutex_unlock(&cgrp->dentry->d_inode->i_mutex);
	if (ret)
		drop_parsed_module_refcounts(opts.subsys_mask);
	return ret;
}

static const struct super_operations cgroup_ops = {
	.statfs = simple_statfs,
	.drop_inode = generic_delete_inode,
	.show_options = cgroup_show_options,
	.remount_fs = cgroup_remount,
};

static void init_cgroup_housekeeping(struct cgroup *cgrp)
{
	INIT_LIST_HEAD(&cgrp->sibling);
	INIT_LIST_HEAD(&cgrp->children);
	INIT_LIST_HEAD(&cgrp->files);
	INIT_LIST_HEAD(&cgrp->cset_links);
	INIT_LIST_HEAD(&cgrp->release_list);
	INIT_LIST_HEAD(&cgrp->pidlists);
	mutex_init(&cgrp->pidlist_mutex);
	INIT_LIST_HEAD(&cgrp->event_list);
	spin_lock_init(&cgrp->event_list_lock);
	simple_xattrs_init(&cgrp->xattrs);
}

static void init_cgroup_root(struct cgroupfs_root *root)
{
	struct cgroup *cgrp = &root->top_cgroup;

	INIT_LIST_HEAD(&root->subsys_list);
	INIT_LIST_HEAD(&root->root_list);
	root->number_of_cgroups = 1;
	cgrp->root = root;
	RCU_INIT_POINTER(cgrp->name, &root_cgroup_name);
	init_cgroup_housekeeping(cgrp);
}

static int cgroup_init_root_id(struct cgroupfs_root *root, int start, int end)
{
	int id;

	lockdep_assert_held(&cgroup_mutex);
	lockdep_assert_held(&cgroup_root_mutex);

	id = idr_alloc_cyclic(&cgroup_hierarchy_idr, root, start, end,
			      GFP_KERNEL);
	if (id < 0)
		return id;

	root->hierarchy_id = id;
	return 0;
}

static void cgroup_exit_root_id(struct cgroupfs_root *root)
{
	lockdep_assert_held(&cgroup_mutex);
	lockdep_assert_held(&cgroup_root_mutex);

	if (root->hierarchy_id) {
		idr_remove(&cgroup_hierarchy_idr, root->hierarchy_id);
		root->hierarchy_id = 0;
	}
}

static int cgroup_test_super(struct super_block *sb, void *data)
{
	struct cgroup_sb_opts *opts = data;
	struct cgroupfs_root *root = sb->s_fs_info;

	/* If we asked for a name then it must match */
	if (opts->name && strcmp(opts->name, root->name))
		return 0;

	/*
	 * If we asked for subsystems (or explicitly for no
	 * subsystems) then they must match
	 */
	if ((opts->subsys_mask || opts->none)
	    && (opts->subsys_mask != root->subsys_mask))
		return 0;

	return 1;
}

static struct cgroupfs_root *cgroup_root_from_opts(struct cgroup_sb_opts *opts)
{
	struct cgroupfs_root *root;

	if (!opts->subsys_mask && !opts->none)
		return NULL;

	root = kzalloc(sizeof(*root), GFP_KERNEL);
	if (!root)
		return ERR_PTR(-ENOMEM);

	init_cgroup_root(root);

	/*
	 * We need to set @root->subsys_mask now so that @root can be
	 * matched by cgroup_test_super() before it finishes
	 * initialization; otherwise, competing mounts with the same
	 * options may try to bind the same subsystems instead of waiting
	 * for the first one leading to unexpected mount errors.
	 * SUBSYS_BOUND will be set once actual binding is complete.
	 */
	root->subsys_mask = opts->subsys_mask;
	root->flags = opts->flags;
	ida_init(&root->cgroup_ida);
	if (opts->release_agent)
		strcpy(root->release_agent_path, opts->release_agent);
	if (opts->name)
		strcpy(root->name, opts->name);
	if (opts->cpuset_clone_children)
		set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->top_cgroup.flags);
	return root;
}

static void cgroup_free_root(struct cgroupfs_root *root)
{
	if (root) {
		/* hierarhcy ID shoulid already have been released */
		WARN_ON_ONCE(root->hierarchy_id);

		ida_destroy(&root->cgroup_ida);
		kfree(root);
	}
}

static int cgroup_set_super(struct super_block *sb, void *data)
{
	int ret;
	struct cgroup_sb_opts *opts = data;

	/* If we don't have a new root, we can't set up a new sb */
	if (!opts->new_root)
		return -EINVAL;

	BUG_ON(!opts->subsys_mask && !opts->none);

	ret = set_anon_super(sb, NULL);
	if (ret)
		return ret;

	sb->s_fs_info = opts->new_root;
	opts->new_root->sb = sb;

	sb->s_blocksize = PAGE_CACHE_SIZE;
	sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
	sb->s_magic = CGROUP_SUPER_MAGIC;
	sb->s_op = &cgroup_ops;

	return 0;
}

static int cgroup_get_rootdir(struct super_block *sb)
{
	static const struct dentry_operations cgroup_dops = {
		.d_iput = cgroup_diput,
		.d_delete = cgroup_delete,
	};

	struct inode *inode =
		cgroup_new_inode(S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR, sb);

	if (!inode)
		return -ENOMEM;

	inode->i_fop = &simple_dir_operations;
	inode->i_op = &cgroup_dir_inode_operations;
	/* directories start off with i_nlink == 2 (for "." entry) */
	inc_nlink(inode);
	sb->s_root = d_make_root(inode);
	if (!sb->s_root)
		return -ENOMEM;
	/* for everything else we want ->d_op set */
	sb->s_d_op = &cgroup_dops;
	return 0;
}

static struct dentry *cgroup_mount(struct file_system_type *fs_type,
			 int flags, const char *unused_dev_name,
			 void *data)
{
	struct cgroup_sb_opts opts;
	struct cgroupfs_root *root;
	int ret = 0;
	struct super_block *sb;
	struct cgroupfs_root *new_root;
	struct inode *inode;

	/* First find the desired set of subsystems */
	mutex_lock(&cgroup_mutex);
	ret = parse_cgroupfs_options(data, &opts);
	mutex_unlock(&cgroup_mutex);
	if (ret)
		goto out_err;

	/*
	 * Allocate a new cgroup root. We may not need it if we're
	 * reusing an existing hierarchy.
	 */
	new_root = cgroup_root_from_opts(&opts);
	if (IS_ERR(new_root)) {
		ret = PTR_ERR(new_root);
		goto drop_modules;
	}
	opts.new_root = new_root;

	/* Locate an existing or new sb for this hierarchy */
	sb = sget(fs_type, cgroup_test_super, cgroup_set_super, 0, &opts);
	if (IS_ERR(sb)) {
		ret = PTR_ERR(sb);
		cgroup_free_root(opts.new_root);
		goto drop_modules;
	}

	root = sb->s_fs_info;
	BUG_ON(!root);
	if (root == opts.new_root) {
		/* We used the new root structure, so this is a new hierarchy */
		struct list_head tmp_links;
		struct cgroup *root_cgrp = &root->top_cgroup;
		struct cgroupfs_root *existing_root;
		const struct cred *cred;
		int i;
		struct css_set *cset;

		BUG_ON(sb->s_root != NULL);

		ret = cgroup_get_rootdir(sb);
		if (ret)
			goto drop_new_super;
		inode = sb->s_root->d_inode;

		mutex_lock(&inode->i_mutex);
		mutex_lock(&cgroup_mutex);
		mutex_lock(&cgroup_root_mutex);

		/* Check for name clashes with existing mounts */
		ret = -EBUSY;
		if (strlen(root->name))
			for_each_active_root(existing_root)
				if (!strcmp(existing_root->name, root->name))
					goto unlock_drop;

		/*
		 * We're accessing css_set_count without locking
		 * css_set_lock here, but that's OK - it can only be
		 * increased by someone holding cgroup_lock, and
		 * that's us. The worst that can happen is that we
		 * have some link structures left over
		 */
		ret = allocate_cgrp_cset_links(css_set_count, &tmp_links);
		if (ret)
			goto unlock_drop;

		/* ID 0 is reserved for dummy root, 1 for unified hierarchy */
		ret = cgroup_init_root_id(root, 2, 0);
		if (ret)
			goto unlock_drop;

		ret = rebind_subsystems(root, root->subsys_mask, 0);
		if (ret == -EBUSY) {
			free_cgrp_cset_links(&tmp_links);
			goto unlock_drop;
		}
		/*
		 * There must be no failure case after here, since rebinding
		 * takes care of subsystems' refcounts, which are explicitly
		 * dropped in the failure exit path.
		 */

		/* EBUSY should be the only error here */
		BUG_ON(ret);

		list_add(&root->root_list, &cgroup_roots);
		cgroup_root_count++;

		sb->s_root->d_fsdata = root_cgrp;
		root->top_cgroup.dentry = sb->s_root;

		/* Link the top cgroup in this hierarchy into all
		 * the css_set objects */
		write_lock(&css_set_lock);
		hash_for_each(css_set_table, i, cset, hlist)
			link_css_set(&tmp_links, cset, root_cgrp);
		write_unlock(&css_set_lock);

		free_cgrp_cset_links(&tmp_links);

		BUG_ON(!list_empty(&root_cgrp->children));
		BUG_ON(root->number_of_cgroups != 1);

		cred = override_creds(&init_cred);
		cgroup_populate_dir(root_cgrp, true, root->subsys_mask);
		revert_creds(cred);
		mutex_unlock(&cgroup_root_mutex);
		mutex_unlock(&cgroup_mutex);
		mutex_unlock(&inode->i_mutex);
	} else {
		/*
		 * We re-used an existing hierarchy - the new root (if
		 * any) is not needed
		 */
		cgroup_free_root(opts.new_root);

		if ((root->flags ^ opts.flags) & CGRP_ROOT_OPTION_MASK) {
			if ((root->flags | opts.flags) & CGRP_ROOT_SANE_BEHAVIOR) {
				pr_err("cgroup: sane_behavior: new mount options should match the existing superblock\n");
				ret = -EINVAL;
				goto drop_new_super;
			} else {
				pr_warning("cgroup: new mount options do not match the existing superblock, will be ignored\n");
			}
		}

		/* no subsys rebinding, so refcounts don't change */
		drop_parsed_module_refcounts(opts.subsys_mask);
	}

	kfree(opts.release_agent);
	kfree(opts.name);
	return dget(sb->s_root);

 unlock_drop:
	cgroup_exit_root_id(root);
	mutex_unlock(&cgroup_root_mutex);
	mutex_unlock(&cgroup_mutex);
	mutex_unlock(&inode->i_mutex);
 drop_new_super:
	deactivate_locked_super(sb);
 drop_modules:
	drop_parsed_module_refcounts(opts.subsys_mask);
 out_err:
	kfree(opts.release_agent);
	kfree(opts.name);
	return ERR_PTR(ret);
}

static void cgroup_kill_sb(struct super_block *sb) {
	struct cgroupfs_root *root = sb->s_fs_info;
	struct cgroup *cgrp = &root->top_cgroup;
	struct cgrp_cset_link *link, *tmp_link;
	int ret;

	BUG_ON(!root);

	BUG_ON(root->number_of_cgroups != 1);
	BUG_ON(!list_empty(&cgrp->children));

	mutex_lock(&cgroup_mutex);
	mutex_lock(&cgroup_root_mutex);

	/* Rebind all subsystems back to the default hierarchy */
	if (root->flags & CGRP_ROOT_SUBSYS_BOUND) {
		ret = rebind_subsystems(root, 0, root->subsys_mask);
		/* Shouldn't be able to fail ... */
		BUG_ON(ret);
	}

	/*
	 * Release all the links from cset_links to this hierarchy's
	 * root cgroup
	 */
	write_lock(&css_set_lock);

	list_for_each_entry_safe(link, tmp_link, &cgrp->cset_links, cset_link) {
		list_del(&link->cset_link);
		list_del(&link->cgrp_link);
		kfree(link);
	}
	write_unlock(&css_set_lock);

	if (!list_empty(&root->root_list)) {
		list_del(&root->root_list);
		cgroup_root_count--;
	}

	cgroup_exit_root_id(root);

	mutex_unlock(&cgroup_root_mutex);
	mutex_unlock(&cgroup_mutex);

	simple_xattrs_free(&cgrp->xattrs);

	kill_litter_super(sb);
	cgroup_free_root(root);
}

static struct file_system_type cgroup_fs_type = {
	.name = "cgroup",
	.mount = cgroup_mount,
	.kill_sb = cgroup_kill_sb,
};

static struct kobject *cgroup_kobj;

/**
 * cgroup_path - generate the path of a cgroup
 * @cgrp: the cgroup in question
 * @buf: the buffer to write the path into
 * @buflen: the length of the buffer
 *
 * Writes path of cgroup into buf.  Returns 0 on success, -errno on error.
 *
 * We can't generate cgroup path using dentry->d_name, as accessing
 * dentry->name must be protected by irq-unsafe dentry->d_lock or parent
 * inode's i_mutex, while on the other hand cgroup_path() can be called
 * with some irq-safe spinlocks held.
 */
int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
{
	int ret = -ENAMETOOLONG;
	char *start;

	if (!cgrp->parent) {
		if (strlcpy(buf, "/", buflen) >= buflen)
			return -ENAMETOOLONG;
		return 0;
	}

	start = buf + buflen - 1;
	*start = '\0';

	rcu_read_lock();
	do {
		const char *name = cgroup_name(cgrp);
		int len;

		len = strlen(name);
		if ((start -= len) < buf)
			goto out;
		memcpy(start, name, len);

		if (--start < buf)
			goto out;
		*start = '/';

		cgrp = cgrp->parent;
	} while (cgrp->parent);
	ret = 0;
	memmove(buf, start, buf + buflen - start);
out:
	rcu_read_unlock();
	return ret;
}
EXPORT_SYMBOL_GPL(cgroup_path);

/**
 * task_cgroup_path - cgroup path of a task in the first cgroup hierarchy
 * @task: target task
 * @buf: the buffer to write the path into
 * @buflen: the length of the buffer
 *
 * Determine @task's cgroup on the first (the one with the lowest non-zero
 * hierarchy_id) cgroup hierarchy and copy its path into @buf.  This
 * function grabs cgroup_mutex and shouldn't be used inside locks used by
 * cgroup controller callbacks.
 *
 * Returns 0 on success, fails with -%ENAMETOOLONG if @buflen is too short.
 */
int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
{
	struct cgroupfs_root *root;
	struct cgroup *cgrp;
	int hierarchy_id = 1, ret = 0;

	if (buflen < 2)
		return -ENAMETOOLONG;

	mutex_lock(&cgroup_mutex);

	root = idr_get_next(&cgroup_hierarchy_idr, &hierarchy_id);

	if (root) {
		cgrp = task_cgroup_from_root(task, root);
		ret = cgroup_path(cgrp, buf, buflen);
	} else {
		/* if no hierarchy exists, everyone is in "/" */
		memcpy(buf, "/", 2);
	}

	mutex_unlock(&cgroup_mutex);
	return ret;
}
EXPORT_SYMBOL_GPL(task_cgroup_path);

/*
 * Control Group taskset
 */
struct task_and_cgroup {
	struct task_struct	*task;
	struct cgroup		*cgrp;
	struct css_set		*cg;
};

struct cgroup_taskset {
	struct task_and_cgroup	single;
	struct flex_array	*tc_array;
	int			tc_array_len;
	int			idx;
	struct cgroup		*cur_cgrp;
};

/**
 * cgroup_taskset_first - reset taskset and return the first task
 * @tset: taskset of interest
 *
 * @tset iteration is initialized and the first task is returned.
 */
struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset)
{
	if (tset->tc_array) {
		tset->idx = 0;
		return cgroup_taskset_next(tset);
	} else {
		tset->cur_cgrp = tset->single.cgrp;
		return tset->single.task;
	}
}
EXPORT_SYMBOL_GPL(cgroup_taskset_first);

/**
 * cgroup_taskset_next - iterate to the next task in taskset
 * @tset: taskset of interest
 *
 * Return the next task in @tset.  Iteration must have been initialized
 * with cgroup_taskset_first().
 */
struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset)
{
	struct task_and_cgroup *tc;

	if (!tset->tc_array || tset->idx >= tset->tc_array_len)
		return NULL;

	tc = flex_array_get(tset->tc_array, tset->idx++);
	tset->cur_cgrp = tc->cgrp;
	return tc->task;
}
EXPORT_SYMBOL_GPL(cgroup_taskset_next);

/**
 * cgroup_taskset_cur_cgroup - return the matching cgroup for the current task
 * @tset: taskset of interest
 *
 * Return the cgroup for the current (last returned) task of @tset.  This
 * function must be preceded by either cgroup_taskset_first() or
 * cgroup_taskset_next().
 */
struct cgroup *cgroup_taskset_cur_cgroup(struct cgroup_taskset *tset)
{
	return tset->cur_cgrp;
}
EXPORT_SYMBOL_GPL(cgroup_taskset_cur_cgroup);

/**
 * cgroup_taskset_size - return the number of tasks in taskset
 * @tset: taskset of interest
 */
int cgroup_taskset_size(struct cgroup_taskset *tset)
{
	return tset->tc_array ? tset->tc_array_len : 1;
}
EXPORT_SYMBOL_GPL(cgroup_taskset_size);


/*
 * cgroup_task_migrate - move a task from one cgroup to another.
 *
 * Must be called with cgroup_mutex and threadgroup locked.
 */
static void cgroup_task_migrate(struct cgroup *old_cgrp,
				struct task_struct *tsk,
				struct css_set *new_cset)
{
	struct css_set *old_cset;

	/*
	 * We are synchronized through threadgroup_lock() against PF_EXITING
	 * setting such that we can't race against cgroup_exit() changing the
	 * css_set to init_css_set and dropping the old one.
	 */
	WARN_ON_ONCE(tsk->flags & PF_EXITING);
	old_cset = task_css_set(tsk);

	task_lock(tsk);
	rcu_assign_pointer(tsk->cgroups, new_cset);
	task_unlock(tsk);

	/* Update the css_set linked lists if we're using them */
	write_lock(&css_set_lock);
	if (!list_empty(&tsk->cg_list))
		list_move(&tsk->cg_list, &new_cset->tasks);
	write_unlock(&css_set_lock);

	/*
	 * We just gained a reference on old_cset by taking it from the
	 * task. As trading it for new_cset is protected by cgroup_mutex,
	 * we're safe to drop it here; it will be freed under RCU.
	 */
	set_bit(CGRP_RELEASABLE, &old_cgrp->flags);
	put_css_set(old_cset);
}

/**
 * cgroup_attach_task - attach a task or a whole threadgroup to a cgroup
 * @cgrp: the cgroup to attach to
 * @tsk: the task or the leader of the threadgroup to be attached
 * @threadgroup: attach the whole threadgroup?
 *
 * Call holding cgroup_mutex and the group_rwsem of the leader. Will take
 * task_lock of @tsk or each thread in the threadgroup individually in turn.
 */
static int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk,
			      bool threadgroup)
{
	int retval, i, group_size;
	struct cgroup_subsys *ss, *failed_ss = NULL;
	struct cgroupfs_root *root = cgrp->root;
	/* threadgroup list cursor and array */
	struct task_struct *leader = tsk;
	struct task_and_cgroup *tc;
	struct flex_array *group;
	struct cgroup_taskset tset = { };

	/*
	 * step 0: in order to do expensive, possibly blocking operations for
	 * every thread, we cannot iterate the thread group list, since it needs
	 * rcu or tasklist locked. instead, build an array of all threads in the
	 * group - group_rwsem prevents new threads from appearing, and if
	 * threads exit, this will just be an over-estimate.
	 */
	if (threadgroup)
		group_size = get_nr_threads(tsk);
	else
		group_size = 1;
	/* flex_array supports very large thread-groups better than kmalloc. */
	group = flex_array_alloc(sizeof(*tc), group_size, GFP_KERNEL);
	if (!group)
		return -ENOMEM;
	/* pre-allocate to guarantee space while iterating in rcu read-side. */
	retval = flex_array_prealloc(group, 0, group_size, GFP_KERNEL);
	if (retval)
		goto out_free_group_list;

	i = 0;
	/*
	 * Prevent freeing of tasks while we take a snapshot. Tasks that are
	 * already PF_EXITING could be freed from underneath us unless we
	 * take an rcu_read_lock.
	 */
	rcu_read_lock();
	do {
		struct task_and_cgroup ent;

		/* @tsk either already exited or can't exit until the end */
		if (tsk->flags & PF_EXITING)
			continue;

		/* as per above, nr_threads may decrease, but not increase. */
		BUG_ON(i >= group_size);
		ent.task = tsk;
		ent.cgrp = task_cgroup_from_root(tsk, root);
		/* nothing to do if this task is already in the cgroup */
		if (ent.cgrp == cgrp)
			continue;
		/*
		 * saying GFP_ATOMIC has no effect here because we did prealloc
		 * earlier, but it's good form to communicate our expectations.
		 */
		retval = flex_array_put(group, i, &ent, GFP_ATOMIC);
		BUG_ON(retval != 0);
		i++;

		if (!threadgroup)
			break;
	} while_each_thread(leader, tsk);
	rcu_read_unlock();
	/* remember the number of threads in the array for later. */
	group_size = i;
	tset.tc_array = group;
	tset.tc_array_len = group_size;

	/* methods shouldn't be called if no task is actually migrating */
	retval = 0;
	if (!group_size)
		goto out_free_group_list;

	/*
	 * step 1: check that we can legitimately attach to the cgroup.
	 */
	for_each_root_subsys(root, ss) {
		if (ss->can_attach) {
			retval = ss->can_attach(cgrp, &tset);
			if (retval) {
				failed_ss = ss;
				goto out_cancel_attach;
			}
		}
	}

	/*
	 * step 2: make sure css_sets exist for all threads to be migrated.
	 * we use find_css_set, which allocates a new one if necessary.
	 */
	for (i = 0; i < group_size; i++) {
		struct css_set *old_cset;

		tc = flex_array_get(group, i);
		old_cset = task_css_set(tc->task);
		tc->cg = find_css_set(old_cset, cgrp);
		if (!tc->cg) {
			retval = -ENOMEM;
			goto out_put_css_set_refs;
		}
	}

	/*
	 * step 3: now that we're guaranteed success wrt the css_sets,
	 * proceed to move all tasks to the new cgroup.  There are no
	 * failure cases after here, so this is the commit point.
	 */
	for (i = 0; i < group_size; i++) {
		tc = flex_array_get(group, i);
		cgroup_task_migrate(tc->cgrp, tc->task, tc->cg);
	}
	/* nothing is sensitive to fork() after this point. */

	/*
	 * step 4: do subsystem attach callbacks.
	 */
	for_each_root_subsys(root, ss) {
		if (ss->attach)
			ss->attach(cgrp, &tset);
	}

	/*
	 * step 5: success! and cleanup
	 */
	retval = 0;
out_put_css_set_refs:
	if (retval) {
		for (i = 0; i < group_size; i++) {
			tc = flex_array_get(group, i);
			if (!tc->cg)
				break;
			put_css_set(tc->cg);
		}
	}
out_cancel_attach:
	if (retval) {
		for_each_root_subsys(root, ss) {
			if (ss == failed_ss)
				break;
			if (ss->cancel_attach)
				ss->cancel_attach(cgrp, &tset);
		}
	}
out_free_group_list:
	flex_array_free(group);
	return retval;
}

/*
 * Find the task_struct of the task to attach by vpid and pass it along to the
 * function to attach either it or all tasks in its threadgroup. Will lock
 * cgroup_mutex and threadgroup; may take task_lock of task.
 */
static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup)
{
	struct task_struct *tsk;
	const struct cred *cred = current_cred(), *tcred;
	int ret;

	if (!cgroup_lock_live_group(cgrp))
		return -ENODEV;

retry_find_task:
	rcu_read_lock();
	if (pid) {
		tsk = find_task_by_vpid(pid);
		if (!tsk) {
			rcu_read_unlock();
			ret= -ESRCH;
			goto out_unlock_cgroup;
		}
		/*
		 * even if we're attaching all tasks in the thread group, we
		 * only need to check permissions on one of them.
		 */
		tcred = __task_cred(tsk);
		if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
		    !uid_eq(cred->euid, tcred->uid) &&
		    !uid_eq(cred->euid, tcred->suid)) {
			rcu_read_unlock();
			ret = -EACCES;
			goto out_unlock_cgroup;
		}
	} else
		tsk = current;

	if (threadgroup)
		tsk = tsk->group_leader;

	/*
	 * Workqueue threads may acquire PF_NO_SETAFFINITY and become
	 * trapped in a cpuset, or RT worker may be born in a cgroup
	 * with no rt_runtime allocated.  Just say no.
	 */
	if (tsk == kthreadd_task || (tsk->flags & PF_NO_SETAFFINITY)) {
		ret = -EINVAL;
		rcu_read_unlock();
		goto out_unlock_cgroup;
	}

	get_task_struct(tsk);
	rcu_read_unlock();

	threadgroup_lock(tsk);
	if (threadgroup) {
		if (!thread_group_leader(tsk)) {
			/*
			 * a race with de_thread from another thread's exec()
			 * may strip us of our leadership, if this happens,
			 * there is no choice but to throw this task away and
			 * try again; this is
			 * "double-double-toil-and-trouble-check locking".
			 */
			threadgroup_unlock(tsk);
			put_task_struct(tsk);
			goto retry_find_task;
		}
	}

	ret = cgroup_attach_task(cgrp, tsk, threadgroup);

	threadgroup_unlock(tsk);

	put_task_struct(tsk);
out_unlock_cgroup:
	mutex_unlock(&cgroup_mutex);
	return ret;
}

/**
 * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
 * @from: attach to all cgroups of a given task
 * @tsk: the task to be attached
 */
int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
{
	struct cgroupfs_root *root;
	int retval = 0;

	mutex_lock(&cgroup_mutex);
	for_each_active_root(root) {
		struct cgroup *from_cg = task_cgroup_from_root(from, root);

		retval = cgroup_attach_task(from_cg, tsk, false);
		if (retval)
			break;
	}
	mutex_unlock(&cgroup_mutex);

	return retval;
}
EXPORT_SYMBOL_GPL(cgroup_attach_task_all);

static int cgroup_tasks_write(struct cgroup *cgrp, struct cftype *cft, u64 pid)
{
	return attach_task_by_pid(cgrp, pid, false);
}

static int cgroup_procs_write(struct cgroup *cgrp, struct cftype *cft, u64 tgid)
{
	return attach_task_by_pid(cgrp, tgid, true);
}

static int cgroup_release_agent_write(struct cgroup *cgrp, struct cftype *cft,
				      const char *buffer)
{
	BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);
	if (strlen(buffer) >= PATH_MAX)
		return -EINVAL;
	if (!cgroup_lock_live_group(cgrp))
		return -ENODEV;
	mutex_lock(&cgroup_root_mutex);
	strcpy(cgrp->root->release_agent_path, buffer);
	mutex_unlock(&cgroup_root_mutex);
	mutex_unlock(&cgroup_mutex);
	return 0;
}

static int cgroup_release_agent_show(struct cgroup *cgrp, struct cftype *cft,
				     struct seq_file *seq)
{
	if (!cgroup_lock_live_group(cgrp))
		return -ENODEV;
	seq_puts(seq, cgrp->root->release_agent_path);
	seq_putc(seq, '\n');
	mutex_unlock(&cgroup_mutex);
	return 0;
}

static int cgroup_sane_behavior_show(struct cgroup *cgrp, struct cftype *cft,
				     struct seq_file *seq)
{
	seq_printf(seq, "%d\n", cgroup_sane_behavior(cgrp));
	return 0;
}

/* A buffer size big enough for numbers or short strings */
#define CGROUP_LOCAL_BUFFER_SIZE 64

static ssize_t cgroup_write_X64(struct cgroup *cgrp, struct cftype *cft,
				struct file *file,
				const char __user *userbuf,
				size_t nbytes, loff_t *unused_ppos)
{
	char buffer[CGROUP_LOCAL_BUFFER_SIZE];
	int retval = 0;
	char *end;

	if (!nbytes)
		return -EINVAL;
	if (nbytes >= sizeof(buffer))
		return -E2BIG;
	if (copy_from_user(buffer, userbuf, nbytes))
		return -EFAULT;

	buffer[nbytes] = 0;     /* nul-terminate */
	if (cft->write_u64) {
		u64 val = simple_strtoull(strstrip(buffer), &end, 0);
		if (*end)
			return -EINVAL;
		retval = cft->write_u64(cgrp, cft, val);
	} else {
		s64 val = simple_strtoll(strstrip(buffer), &end, 0);
		if (*end)
			return -EINVAL;
		retval = cft->write_s64(cgrp, cft, val);
	}
	if (!retval)
		retval = nbytes;
	return retval;
}

static ssize_t cgroup_write_string(struct cgroup *cgrp, struct cftype *cft,
				   struct file *file,
				   const char __user *userbuf,
				   size_t nbytes, loff_t *unused_ppos)
{
	char local_buffer[CGROUP_LOCAL_BUFFER_SIZE];
	int retval = 0;
	size_t max_bytes = cft->max_write_len;
	char *buffer = local_buffer;

	if (!max_bytes)
		max_bytes = sizeof(local_buffer) - 1;
	if (nbytes >= max_bytes)
		return -E2BIG;
	/* Allocate a dynamic buffer if we need one */
	if (nbytes >= sizeof(local_buffer)) {
		buffer = kmalloc(nbytes + 1, GFP_KERNEL);
		if (buffer == NULL)
			return -ENOMEM;
	}
	if (nbytes && copy_from_user(buffer, userbuf, nbytes)) {
		retval = -EFAULT;
		goto out;
	}

	buffer[nbytes] = 0;     /* nul-terminate */
	retval = cft->write_string(cgrp, cft, strstrip(buffer));
	if (!retval)
		retval = nbytes;
out:
	if (buffer != local_buffer)
		kfree(buffer);
	return retval;
}

static ssize_t cgroup_file_write(struct file *file, const char __user *buf,
						size_t nbytes, loff_t *ppos)
{
	struct cftype *cft = __d_cft(file->f_dentry);
	struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);

	if (cgroup_is_dead(cgrp))
		return -ENODEV;
	if (cft->write)
		return cft->write(cgrp, cft, file, buf, nbytes, ppos);
	if (cft->write_u64 || cft->write_s64)
		return cgroup_write_X64(cgrp, cft, file, buf, nbytes, ppos);
	if (cft->write_string)
		return cgroup_write_string(cgrp, cft, file, buf, nbytes, ppos);
	if (cft->trigger) {
		int ret = cft->trigger(cgrp, (unsigned int)cft->private);
		return ret ? ret : nbytes;
	}
	return -EINVAL;
}

static ssize_t cgroup_read_u64(struct cgroup *cgrp, struct cftype *cft,
			       struct file *file,
			       char __user *buf, size_t nbytes,
			       loff_t *ppos)
{
	char tmp[CGROUP_LOCAL_BUFFER_SIZE];
	u64 val = cft->read_u64(cgrp, cft);
	int len = sprintf(tmp, "%llu\n", (unsigned long long) val);

	return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
}

static ssize_t cgroup_read_s64(struct cgroup *cgrp, struct cftype *cft,
			       struct file *file,
			       char __user *buf, size_t nbytes,
			       loff_t *ppos)
{
	char tmp[CGROUP_LOCAL_BUFFER_SIZE];
	s64 val = cft->read_s64(cgrp, cft);
	int len = sprintf(tmp, "%lld\n", (long long) val);

	return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
}

static ssize_t cgroup_file_read(struct file *file, char __user *buf,
				   size_t nbytes, loff_t *ppos)
{
	struct cftype *cft = __d_cft(file->f_dentry);
	struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);

	if (cgroup_is_dead(cgrp))
		return -ENODEV;

	if (cft->read)
		return cft->read(cgrp, cft, file, buf, nbytes, ppos);
	if (cft->read_u64)
		return cgroup_read_u64(cgrp, cft, file, buf, nbytes, ppos);
	if (cft->read_s64)
		return cgroup_read_s64(cgrp, cft, file, buf, nbytes, ppos);
	return -EINVAL;
}

/*
 * seqfile ops/methods for returning structured data. Currently just
 * supports string->u64 maps, but can be extended in future.
 */

struct cgroup_seqfile_state {
	struct cftype *cft;
	struct cgroup *cgroup;
};

static int cgroup_map_add(struct cgroup_map_cb *cb, const char *key, u64 value)
{
	struct seq_file *sf = cb->state;
	return seq_printf(sf, "%s %llu\n", key, (unsigned long long)value);
}

static int cgroup_seqfile_show(struct seq_file *m, void *arg)
{
	struct cgroup_seqfile_state *state = m->private;
	struct cftype *cft = state->cft;
	if (cft->read_map) {
		struct cgroup_map_cb cb = {
			.fill = cgroup_map_add,
			.state = m,
		};
		return cft->read_map(state->cgroup, cft, &cb);
	}
	return cft->read_seq_string(state->cgroup, cft, m);
}

static int cgroup_seqfile_release(struct inode *inode, struct file *file)
{
	struct seq_file *seq = file->private_data;
	kfree(seq->private);
	return single_release(inode, file);
}

static const struct file_operations cgroup_seqfile_operations = {
	.read = seq_read,
	.write = cgroup_file_write,
	.llseek = seq_lseek,
	.release = cgroup_seqfile_release,
};

static int cgroup_file_open(struct inode *inode, struct file *file)
{
	int err;
	struct cftype *cft;

	err = generic_file_open(inode, file);
	if (err)
		return err;
	cft = __d_cft(file->f_dentry);

	if (cft->read_map || cft->read_seq_string) {
		struct cgroup_seqfile_state *state;

		state = kzalloc(sizeof(*state), GFP_USER);
		if (!state)
			return -ENOMEM;

		state->cft = cft;
		state->cgroup = __d_cgrp(file->f_dentry->d_parent);
		file->f_op = &cgroup_seqfile_operations;
		err = single_open(file, cgroup_seqfile_show, state);
		if (err < 0)
			kfree(state);
	} else if (cft->open)
		err = cft->open(inode, file);
	else
		err = 0;

	return err;
}

static int cgroup_file_release(struct inode *inode, struct file *file)
{
	struct cftype *cft = __d_cft(file->f_dentry);
	if (cft->release)
		return cft->release(inode, file);
	return 0;
}

/*
 * cgroup_rename - Only allow simple rename of directories in place.
 */
static int cgroup_rename(struct inode *old_dir, struct dentry *old_dentry,
			    struct inode *new_dir, struct dentry *new_dentry)
{
	int ret;
	struct cgroup_name *name, *old_name;
	struct cgroup *cgrp;

	/*
	 * It's convinient to use parent dir's i_mutex to protected
	 * cgrp->name.
	 */
	lockdep_assert_held(&old_dir->i_mutex);

	if (!S_ISDIR(old_dentry->d_inode->i_mode))
		return -ENOTDIR;
	if (new_dentry->d_inode)
		return -EEXIST;
	if (old_dir != new_dir)
		return -EIO;

	cgrp = __d_cgrp(old_dentry);

	/*
	 * This isn't a proper migration and its usefulness is very
	 * limited.  Disallow if sane_behavior.
	 */
	if (cgroup_sane_behavior(cgrp))
		return -EPERM;

	name = cgroup_alloc_name(new_dentry);
	if (!name)
		return -ENOMEM;

	ret = simple_rename(old_dir, old_dentry, new_dir, new_dentry);
	if (ret) {
		kfree(name);
		return ret;
	}

	old_name = rcu_dereference_protected(cgrp->name, true);
	rcu_assign_pointer(cgrp->name, name);

	kfree_rcu(old_name, rcu_head);
	return 0;
}

static struct simple_xattrs *__d_xattrs(struct dentry *dentry)
{
	if (S_ISDIR(dentry->d_inode->i_mode))
		return &__d_cgrp(dentry)->xattrs;
	else
		return &__d_cfe(dentry)->xattrs;
}

static inline int xattr_enabled(struct dentry *dentry)
{
	struct cgroupfs_root *root = dentry->d_sb->s_fs_info;
	return root->flags & CGRP_ROOT_XATTR;
}

static bool is_valid_xattr(const char *name)
{
	if (!strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN) ||
	    !strncmp(name, XATTR_SECURITY_PREFIX, XATTR_SECURITY_PREFIX_LEN))
		return true;
	return false;
}

static int cgroup_setxattr(struct dentry *dentry, const char *name,
			   const void *val, size_t size, int flags)
{
	if (!xattr_enabled(dentry))
		return -EOPNOTSUPP;
	if (!is_valid_xattr(name))
		return -EINVAL;
	return simple_xattr_set(__d_xattrs(dentry), name, val, size, flags);
}

static int cgroup_removexattr(struct dentry *dentry, const char *name)
{
	if (!xattr_enabled(dentry))
		return -EOPNOTSUPP;
	if (!is_valid_xattr(name))
		return -EINVAL;
	return simple_xattr_remove(__d_xattrs(dentry), name);
}

static ssize_t cgroup_getxattr(struct dentry *dentry, const char *name,
			       void *buf, size_t size)
{
	if (!xattr_enabled(dentry))
		return -EOPNOTSUPP;
	if (!is_valid_xattr(name))
		return -EINVAL;
	return simple_xattr_get(__d_xattrs(dentry), name, buf, size);
}

static ssize_t cgroup_listxattr(struct dentry *dentry, char *buf, size_t size)
{
	if (!xattr_enabled(dentry))
		return -EOPNOTSUPP;
	return simple_xattr_list(__d_xattrs(dentry), buf, size);
}

static const struct file_operations cgroup_file_operations = {
	.read = cgroup_file_read,
	.write = cgroup_file_write,
	.llseek = generic_file_llseek,
	.open = cgroup_file_open,
	.release = cgroup_file_release,
};

static const struct inode_operations cgroup_file_inode_operations = {
	.setxattr = cgroup_setxattr,
	.getxattr = cgroup_getxattr,
	.listxattr = cgroup_listxattr,
	.removexattr = cgroup_removexattr,
};

static const struct inode_operations cgroup_dir_inode_operations = {
	.lookup = simple_lookup,
	.mkdir = cgroup_mkdir,
	.rmdir = cgroup_rmdir,
	.rename = cgroup_rename,
	.setxattr = cgroup_setxattr,
	.getxattr = cgroup_getxattr,
	.listxattr = cgroup_listxattr,
	.removexattr = cgroup_removexattr,
};

/*
 * Check if a file is a control file
 */
static inline struct cftype *__file_cft(struct file *file)
{
	if (file_inode(file)->i_fop != &cgroup_file_operations)
		return ERR_PTR(-EINVAL);
	return __d_cft(file->f_dentry);
}

static int cgroup_create_file(struct dentry *dentry, umode_t mode,
				struct super_block *sb)
{
	struct inode *inode;

	if (!dentry)
		return -ENOENT;
	if (dentry->d_inode)
		return -EEXIST;

	inode = cgroup_new_inode(mode, sb);
	if (!inode)
		return -ENOMEM;

	if (S_ISDIR(mode)) {
		inode->i_op = &cgroup_dir_inode_operations;
		inode->i_fop = &simple_dir_operations;

		/* start off with i_nlink == 2 (for "." entry) */
		inc_nlink(inode);
		inc_nlink(dentry->d_parent->d_inode);

		/*
		 * Control reaches here with cgroup_mutex held.
		 * @inode->i_mutex should nest outside cgroup_mutex but we
		 * want to populate it immediately without releasing
		 * cgroup_mutex.  As @inode isn't visible to anyone else
		 * yet, trylock will always succeed without affecting
		 * lockdep checks.
		 */
		WARN_ON_ONCE(!mutex_trylock(&inode->i_mutex));
	} else if (S_ISREG(mode)) {
		inode->i_size = 0;
		inode->i_fop = &cgroup_file_operations;
		inode->i_op = &cgroup_file_inode_operations;
	}
	d_instantiate(dentry, inode);
	dget(dentry);	/* Extra count - pin the dentry in core */
	return 0;
}

/**
 * cgroup_file_mode - deduce file mode of a control file
 * @cft: the control file in question
 *
 * returns cft->mode if ->mode is not 0
 * returns S_IRUGO|S_IWUSR if it has both a read and a write handler
 * returns S_IRUGO if it has only a read handler
 * returns S_IWUSR if it has only a write hander
 */
static umode_t cgroup_file_mode(const struct cftype *cft)
{
	umode_t mode = 0;

	if (cft->mode)
		return cft->mode;

	if (cft->read || cft->read_u64 || cft->read_s64 ||
	    cft->read_map || cft->read_seq_string)
		mode |= S_IRUGO;

	if (cft->write || cft->write_u64 || cft->write_s64 ||
	    cft->write_string || cft->trigger)
		mode |= S_IWUSR;

	return mode;
}

static int cgroup_add_file(struct cgroup *cgrp, struct cgroup_subsys *subsys,
			   struct cftype *cft)
{
	struct dentry *dir = cgrp->dentry;
	struct cgroup *parent = __d_cgrp(dir);
	struct dentry *dentry;
	struct cfent *cfe;
	int error;
	umode_t mode;
	char name[MAX_CGROUP_TYPE_NAMELEN + MAX_CFTYPE_NAME + 2] = { 0 };

	if (subsys && !(cgrp->root->flags & CGRP_ROOT_NOPREFIX)) {
		strcpy(name, subsys->name);
		strcat(name, ".");
	}
	strcat(name, cft->name);

	BUG_ON(!mutex_is_locked(&dir->d_inode->i_mutex));

	cfe = kzalloc(sizeof(*cfe), GFP_KERNEL);
	if (!cfe)
		return -ENOMEM;

	dentry = lookup_one_len(name, dir, strlen(name));
	if (IS_ERR(dentry)) {
		error = PTR_ERR(dentry);
		goto out;
	}

	cfe->type = (void *)cft;
	cfe->dentry = dentry;
	dentry->d_fsdata = cfe;
	simple_xattrs_init(&cfe->xattrs);

	mode = cgroup_file_mode(cft);
	error = cgroup_create_file(dentry, mode | S_IFREG, cgrp->root->sb);
	if (!error) {
		list_add_tail(&cfe->node, &parent->files);
		cfe = NULL;
	}
	dput(dentry);
out:
	kfree(cfe);
	return error;
}

static int cgroup_addrm_files(struct cgroup *cgrp, struct cgroup_subsys *subsys,
			      struct cftype cfts[], bool is_add)
{
	struct cftype *cft;
	int err, ret = 0;

	for (cft = cfts; cft->name[0] != '\0'; cft++) {
		/* does cft->flags tell us to skip this file on @cgrp? */
		if ((cft->flags & CFTYPE_INSANE) && cgroup_sane_behavior(cgrp))
			continue;
		if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgrp->parent)
			continue;
		if ((cft->flags & CFTYPE_ONLY_ON_ROOT) && cgrp->parent)
			continue;

		if (is_add) {
			err = cgroup_add_file(cgrp, subsys, cft);
			if (err)
				pr_warn("cgroup_addrm_files: failed to add %s, err=%d\n",
					cft->name, err);
			ret = err;
		} else {
			cgroup_rm_file(cgrp, cft);
		}
	}
	return ret;
}

static void cgroup_cfts_prepare(void)
	__acquires(&cgroup_mutex)
{
	/*
	 * Thanks to the entanglement with vfs inode locking, we can't walk
	 * the existing cgroups under cgroup_mutex and create files.
	 * Instead, we use cgroup_for_each_descendant_pre() and drop RCU
	 * read lock before calling cgroup_addrm_files().
	 */
	mutex_lock(&cgroup_mutex);
}

static void cgroup_cfts_commit(struct cgroup_subsys *ss,
			       struct cftype *cfts, bool is_add)
	__releases(&cgroup_mutex)
{
	LIST_HEAD(pending);
	struct cgroup *cgrp, *root = &ss->root->top_cgroup;
	struct super_block *sb = ss->root->sb;
	struct dentry *prev = NULL;
	struct inode *inode;
	u64 update_before;

	/* %NULL @cfts indicates abort and don't bother if @ss isn't attached */
	if (!cfts || ss->root == &cgroup_dummy_root ||
	    !atomic_inc_not_zero(&sb->s_active)) {
		mutex_unlock(&cgroup_mutex);
		return;
	}

	/*
	 * All cgroups which are created after we drop cgroup_mutex will
	 * have the updated set of files, so we only need to update the
	 * cgroups created before the current @cgroup_serial_nr_next.
	 */
	update_before = cgroup_serial_nr_next;

	mutex_unlock(&cgroup_mutex);

	/* @root always needs to be updated */
	inode = root->dentry->d_inode;
	mutex_lock(&inode->i_mutex);
	mutex_lock(&cgroup_mutex);
	cgroup_addrm_files(root, ss, cfts, is_add);
	mutex_unlock(&cgroup_mutex);
	mutex_unlock(&inode->i_mutex);

	/* add/rm files for all cgroups created before */
	rcu_read_lock();
	cgroup_for_each_descendant_pre(cgrp, root) {
		if (cgroup_is_dead(cgrp))
			continue;

		inode = cgrp->dentry->d_inode;
		dget(cgrp->dentry);
		rcu_read_unlock();

		dput(prev);
		prev = cgrp->dentry;

		mutex_lock(&inode->i_mutex);
		mutex_lock(&cgroup_mutex);
		if (cgrp->serial_nr < update_before && !cgroup_is_dead(cgrp))
			cgroup_addrm_files(cgrp, ss, cfts, is_add);
		mutex_unlock(&cgroup_mutex);
		mutex_unlock(&inode->i_mutex);

		rcu_read_lock();
	}
	rcu_read_unlock();
	dput(prev);
	deactivate_super(sb);
}

/**
 * cgroup_add_cftypes - add an array of cftypes to a subsystem
 * @ss: target cgroup subsystem
 * @cfts: zero-length name terminated array of cftypes
 *
 * Register @cfts to @ss.  Files described by @cfts are created for all
 * existing cgroups to which @ss is attached and all future cgroups will
 * have them too.  This function can be called anytime whether @ss is
 * attached or not.
 *
 * Returns 0 on successful registration, -errno on failure.  Note that this
 * function currently returns 0 as long as @cfts registration is successful
 * even if some file creation attempts on existing cgroups fail.
 */
int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
{
	struct cftype_set *set;

	set = kzalloc(sizeof(*set), GFP_KERNEL);
	if (!set)
		return -ENOMEM;

	cgroup_cfts_prepare();
	set->cfts = cfts;
	list_add_tail(&set->node, &ss->cftsets);
	cgroup_cfts_commit(ss, cfts, true);

	return 0;
}
EXPORT_SYMBOL_GPL(cgroup_add_cftypes);

/**
 * cgroup_rm_cftypes - remove an array of cftypes from a subsystem
 * @ss: target cgroup subsystem
 * @cfts: zero-length name terminated array of cftypes
 *
 * Unregister @cfts from @ss.  Files described by @cfts are removed from
 * all existing cgroups to which @ss is attached and all future cgroups
 * won't have them either.  This function can be called anytime whether @ss
 * is attached or not.
 *
 * Returns 0 on successful unregistration, -ENOENT if @cfts is not
 * registered with @ss.
 */
int cgroup_rm_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
{
	struct cftype_set *set;

	cgroup_cfts_prepare();

	list_for_each_entry(set, &ss->cftsets, node) {
		if (set->cfts == cfts) {
			list_del(&set->node);
			kfree(set);
			cgroup_cfts_commit(ss, cfts, false);
			return 0;
		}
	}

	cgroup_cfts_commit(ss, NULL, false);
	return -ENOENT;
}

/**
 * cgroup_task_count - count the number of tasks in a cgroup.
 * @cgrp: the cgroup in question
 *
 * Return the number of tasks in the cgroup.
 */
int cgroup_task_count(const struct cgroup *cgrp)
{
	int count = 0;
	struct cgrp_cset_link *link;

	read_lock(&css_set_lock);
	list_for_each_entry(link, &cgrp->cset_links, cset_link)
		count += atomic_read(&link->cset->refcount);
	read_unlock(&css_set_lock);
	return count;
}

/*
 * Advance a list_head iterator.  The iterator should be positioned at
 * the start of a css_set
 */
static void cgroup_advance_iter(struct cgroup *cgrp, struct cgroup_iter *it)
{
	struct list_head *l = it->cset_link;
	struct cgrp_cset_link *link;
	struct css_set *cset;

	/* Advance to the next non-empty css_set */
	do {
		l = l->next;
		if (l == &cgrp->cset_links) {
			it->cset_link = NULL;
			return;
		}
		link = list_entry(l, struct cgrp_cset_link, cset_link);
		cset = link->cset;
	} while (list_empty(&cset->tasks));
	it->cset_link = l;
	it->task = cset->tasks.next;
}

/*
 * To reduce the fork() overhead for systems that are not actually
 * using their cgroups capability, we don't maintain the lists running
 * through each css_set to its tasks until we see the list actually
 * used - in other words after the first call to cgroup_iter_start().
 */
static void cgroup_enable_task_cg_lists(void)
{
	struct task_struct *p, *g;
	write_lock(&css_set_lock);
	use_task_css_set_links = 1;
	/*
	 * We need tasklist_lock because RCU is not safe against
	 * while_each_thread(). Besides, a forking task that has passed
	 * cgroup_post_fork() without seeing use_task_css_set_links = 1
	 * is not guaranteed to have its child immediately visible in the
	 * tasklist if we walk through it with RCU.
	 */
	read_lock(&tasklist_lock);
	do_each_thread(g, p) {
		task_lock(p);
		/*
		 * We should check if the process is exiting, otherwise
		 * it will race with cgroup_exit() in that the list
		 * entry won't be deleted though the process has exited.
		 */
		if (!(p->flags & PF_EXITING) && list_empty(&p->cg_list))
			list_add(&p->cg_list, &task_css_set(p)->tasks);
		task_unlock(p);
	} while_each_thread(g, p);
	read_unlock(&tasklist_lock);
	write_unlock(&css_set_lock);
}

/**
 * cgroup_next_sibling - find the next sibling of a given cgroup
 * @pos: the current cgroup
 *
 * This function returns the next sibling of @pos and should be called
 * under RCU read lock.  The only requirement is that @pos is accessible.
 * The next sibling is guaranteed to be returned regardless of @pos's
 * state.
 */
struct cgroup *cgroup_next_sibling(struct cgroup *pos)
{
	struct cgroup *next;

	WARN_ON_ONCE(!rcu_read_lock_held());

	/*
	 * @pos could already have been removed.  Once a cgroup is removed,
	 * its ->sibling.next is no longer updated when its next sibling
	 * changes.  As CGRP_DEAD assertion is serialized and happens
	 * before the cgroup is taken off the ->sibling list, if we see it
	 * unasserted, it's guaranteed that the next sibling hasn't
	 * finished its grace period even if it's already removed, and thus
	 * safe to dereference from this RCU critical section.  If
	 * ->sibling.next is inaccessible, cgroup_is_dead() is guaranteed
	 * to be visible as %true here.
	 */
	if (likely(!cgroup_is_dead(pos))) {
		next = list_entry_rcu(pos->sibling.next, struct cgroup, sibling);
		if (&next->sibling != &pos->parent->children)
			return next;
		return NULL;
	}

	/*
	 * Can't dereference the next pointer.  Each cgroup is given a
	 * monotonically increasing unique serial number and always
	 * appended to the sibling list, so the next one can be found by
	 * walking the parent's children until we see a cgroup with higher
	 * serial number than @pos's.
	 *
	 * While this path can be slow, it's taken only when either the
	 * current cgroup is removed or iteration and removal race.
	 */
	list_for_each_entry_rcu(next, &pos->parent->children, sibling)
		if (next->serial_nr > pos->serial_nr)
			return next;
	return NULL;
}
EXPORT_SYMBOL_GPL(cgroup_next_sibling);

/**
 * cgroup_next_descendant_pre - find the next descendant for pre-order walk
 * @pos: the current position (%NULL to initiate traversal)
 * @cgroup: cgroup whose descendants to walk
 *
 * To be used by cgroup_for_each_descendant_pre().  Find the next
 * descendant to visit for pre-order traversal of @cgroup's descendants.
 *
 * While this function requires RCU read locking, it doesn't require the
 * whole traversal to be contained in a single RCU critical section.  This
 * function will return the correct next descendant as long as both @pos
 * and @cgroup are accessible and @pos is a descendant of @cgroup.
 */
struct cgroup *cgroup_next_descendant_pre(struct cgroup *pos,
					  struct cgroup *cgroup)
{
	struct cgroup *next;

	WARN_ON_ONCE(!rcu_read_lock_held());

	/* if first iteration, pretend we just visited @cgroup */
	if (!pos)
		pos = cgroup;

	/* visit the first child if exists */
	next = list_first_or_null_rcu(&pos->children, struct cgroup, sibling);
	if (next)
		return next;

	/* no child, visit my or the closest ancestor's next sibling */
	while (pos != cgroup) {
		next = cgroup_next_sibling(pos);
		if (next)
			return next;
		pos = pos->parent;
	}

	return NULL;
}
EXPORT_SYMBOL_GPL(cgroup_next_descendant_pre);

/**
 * cgroup_rightmost_descendant - return the rightmost descendant of a cgroup
 * @pos: cgroup of interest
 *
 * Return the rightmost descendant of @pos.  If there's no descendant,
 * @pos is returned.  This can be used during pre-order traversal to skip
 * subtree of @pos.
 *
 * While this function requires RCU read locking, it doesn't require the
 * whole traversal to be contained in a single RCU critical section.  This
 * function will return the correct rightmost descendant as long as @pos is
 * accessible.
 */
struct cgroup *cgroup_rightmost_descendant(struct cgroup *pos)
{
	struct cgroup *last, *tmp;

	WARN_ON_ONCE(!rcu_read_lock_held());

	do {
		last = pos;
		/* ->prev isn't RCU safe, walk ->next till the end */
		pos = NULL;
		list_for_each_entry_rcu(tmp, &last->children, sibling)
			pos = tmp;
	} while (pos);

	return last;
}
EXPORT_SYMBOL_GPL(cgroup_rightmost_descendant);

static struct cgroup *cgroup_leftmost_descendant(struct cgroup *pos)
{
	struct cgroup *last;

	do {
		last = pos;
		pos = list_first_or_null_rcu(&pos->children, struct cgroup,
					     sibling);
	} while (pos);

	return last;
}

/**
 * cgroup_next_descendant_post - find the next descendant for post-order walk
 * @pos: the current position (%NULL to initiate traversal)
 * @cgroup: cgroup whose descendants to walk
 *
 * To be used by cgroup_for_each_descendant_post().  Find the next
 * descendant to visit for post-order traversal of @cgroup's descendants.
 *
 * While this function requires RCU read locking, it doesn't require the
 * whole traversal to be contained in a single RCU critical section.  This
 * function will return the correct next descendant as long as both @pos
 * and @cgroup are accessible and @pos is a descendant of @cgroup.
 */
struct cgroup *cgroup_next_descendant_post(struct cgroup *pos,
					   struct cgroup *cgroup)
{
	struct cgroup *next;

	WARN_ON_ONCE(!rcu_read_lock_held());

	/* if first iteration, visit the leftmost descendant */
	if (!pos) {
		next = cgroup_leftmost_descendant(cgroup);
		return next != cgroup ? next : NULL;
	}

	/* if there's an unvisited sibling, visit its leftmost descendant */
	next = cgroup_next_sibling(pos);
	if (next)
		return cgroup_leftmost_descendant(next);

	/* no sibling left, visit parent */
	next = pos->parent;
	return next != cgroup ? next : NULL;
}
EXPORT_SYMBOL_GPL(cgroup_next_descendant_post);

void cgroup_iter_start(struct cgroup *cgrp, struct cgroup_iter *it)
	__acquires(css_set_lock)
{
	/*
	 * The first time anyone tries to iterate across a cgroup,
	 * we need to enable the list linking each css_set to its
	 * tasks, and fix up all existing tasks.
	 */
	if (!use_task_css_set_links)
		cgroup_enable_task_cg_lists();

	read_lock(&css_set_lock);
	it->cset_link = &cgrp->cset_links;
	cgroup_advance_iter(cgrp, it);
}

struct task_struct *cgroup_iter_next(struct cgroup *cgrp,
					struct cgroup_iter *it)
{
	struct task_struct *res;
	struct list_head *l = it->task;
	struct cgrp_cset_link *link;

	/* If the iterator cg is NULL, we have no tasks */
	if (!it->cset_link)
		return NULL;
	res = list_entry(l, struct task_struct, cg_list);
	/* Advance iterator to find next entry */
	l = l->next;
	link = list_entry(it->cset_link, struct cgrp_cset_link, cset_link);
	if (l == &link->cset->tasks) {
		/* We reached the end of this task list - move on to
		 * the next cg_cgroup_link */
		cgroup_advance_iter(cgrp, it);
	} else {
		it->task = l;
	}
	return res;
}

void cgroup_iter_end(struct cgroup *cgrp, struct cgroup_iter *it)
	__releases(css_set_lock)
{
	read_unlock(&css_set_lock);
}

static inline int started_after_time(struct task_struct *t1,
				     struct timespec *time,
				     struct task_struct *t2)
{
	int start_diff = timespec_compare(&t1->start_time, time);
	if (start_diff > 0) {
		return 1;
	} else if (start_diff < 0) {
		return 0;
	} else {
		/*
		 * Arbitrarily, if two processes started at the same
		 * time, we'll say that the lower pointer value
		 * started first. Note that t2 may have exited by now
		 * so this may not be a valid pointer any longer, but
		 * that's fine - it still serves to distinguish
		 * between two tasks started (effectively) simultaneously.
		 */
		return t1 > t2;
	}
}

/*
 * This function is a callback from heap_insert() and is used to order
 * the heap.
 * In this case we order the heap in descending task start time.
 */
static inline int started_after(void *p1, void *p2)
{
	struct task_struct *t1 = p1;
	struct task_struct *t2 = p2;
	return started_after_time(t1, &t2->start_time, t2);
}

/**
 * cgroup_scan_tasks - iterate though all the tasks in a cgroup
 * @scan: struct cgroup_scanner containing arguments for the scan
 *
 * Arguments include pointers to callback functions test_task() and
 * process_task().
 * Iterate through all the tasks in a cgroup, calling test_task() for each,
 * and if it returns true, call process_task() for it also.
 * The test_task pointer may be NULL, meaning always true (select all tasks).
 * Effectively duplicates cgroup_iter_{start,next,end}()
 * but does not lock css_set_lock for the call to process_task().
 * The struct cgroup_scanner may be embedded in any structure of the caller's
 * creation.
 * It is guaranteed that process_task() will act on every task that
 * is a member of the cgroup for the duration of this call. This
 * function may or may not call process_task() for tasks that exit
 * or move to a different cgroup during the call, or are forked or
 * move into the cgroup during the call.
 *
 * Note that test_task() may be called with locks held, and may in some
 * situations be called multiple times for the same task, so it should
 * be cheap.
 * If the heap pointer in the struct cgroup_scanner is non-NULL, a heap has been
 * pre-allocated and will be used for heap operations (and its "gt" member will
 * be overwritten), else a temporary heap will be used (allocation of which
 * may cause this function to fail).
 */
int cgroup_scan_tasks(struct cgroup_scanner *scan)
{
	int retval, i;
	struct cgroup_iter it;
	struct task_struct *p, *dropped;
	/* Never dereference latest_task, since it's not refcounted */
	struct task_struct *latest_task = NULL;
	struct ptr_heap tmp_heap;
	struct ptr_heap *heap;
	struct timespec latest_time = { 0, 0 };

	if (scan->heap) {
		/* The caller supplied our heap and pre-allocated its memory */
		heap = scan->heap;
		heap->gt = &started_after;
	} else {
		/* We need to allocate our own heap memory */
		heap = &tmp_heap;
		retval = heap_init(heap, PAGE_SIZE, GFP_KERNEL, &started_after);
		if (retval)
			/* cannot allocate the heap */
			return retval;
	}

 again:
	/*
	 * Scan tasks in the cgroup, using the scanner's "test_task" callback
	 * to determine which are of interest, and using the scanner's
	 * "process_task" callback to process any of them that need an update.
	 * Since we don't want to hold any locks during the task updates,
	 * gather tasks to be processed in a heap structure.
	 * The heap is sorted by descending task start time.
	 * If the statically-sized heap fills up, we overflow tasks that
	 * started later, and in future iterations only consider tasks that
	 * started after the latest task in the previous pass. This
	 * guarantees forward progress and that we don't miss any tasks.
	 */
	heap->size = 0;
	cgroup_iter_start(scan->cg, &it);
	while ((p = cgroup_iter_next(scan->cg, &it))) {
		/*
		 * Only affect tasks that qualify per the caller's callback,
		 * if he provided one
		 */
		if (scan->test_task && !scan->test_task(p, scan))
			continue;
		/*
		 * Only process tasks that started after the last task
		 * we processed
		 */
		if (!started_after_time(p, &latest_time, latest_task))
			continue;
		dropped = heap_insert(heap, p);
		if (dropped == NULL) {
			/*
			 * The new task was inserted; the heap wasn't
			 * previously full
			 */
			get_task_struct(p);
		} else if (dropped != p) {
			/*
			 * The new task was inserted, and pushed out a
			 * different task
			 */
			get_task_struct(p);
			put_task_struct(dropped);
		}
		/*
		 * Else the new task was newer than anything already in
		 * the heap and wasn't inserted
		 */
	}
	cgroup_iter_end(scan->cg, &it);

	if (heap->size) {
		for (i = 0; i < heap->size; i++) {
			struct task_struct *q = heap->ptrs[i];
			if (i == 0) {
				latest_time = q->start_time;
				latest_task = q;
			}
			/* Process the task per the caller's callback */
			scan->process_task(q, scan);
			put_task_struct(q);
		}
		/*
		 * If we had to process any tasks at all, scan again
		 * in case some of them were in the middle of forking
		 * children that didn't get processed.
		 * Not the most efficient way to do it, but it avoids
		 * having to take callback_mutex in the fork path
		 */
		goto again;
	}
	if (heap == &tmp_heap)
		heap_free(&tmp_heap);
	return 0;
}

static void cgroup_transfer_one_task(struct task_struct *task,
				     struct cgroup_scanner *scan)
{
	struct cgroup *new_cgroup = scan->data;

	mutex_lock(&cgroup_mutex);
	cgroup_attach_task(new_cgroup, task, false);
	mutex_unlock(&cgroup_mutex);
}

/**
 * cgroup_trasnsfer_tasks - move tasks from one cgroup to another
 * @to: cgroup to which the tasks will be moved
 * @from: cgroup in which the tasks currently reside
 */
int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
{
	struct cgroup_scanner scan;

	scan.cg = from;
	scan.test_task = NULL; /* select all tasks in cgroup */
	scan.process_task = cgroup_transfer_one_task;
	scan.heap = NULL;
	scan.data = to;

	return cgroup_scan_tasks(&scan);
}

/*
 * Stuff for reading the 'tasks'/'procs' files.
 *
 * Reading this file can return large amounts of data if a cgroup has
 * *lots* of attached tasks. So it may need several calls to read(),
 * but we cannot guarantee that the information we produce is correct
 * unless we produce it entirely atomically.
 *
 */

/* which pidlist file are we talking about? */
enum cgroup_filetype {
	CGROUP_FILE_PROCS,
	CGROUP_FILE_TASKS,
};

/*
 * A pidlist is a list of pids that virtually represents the contents of one
 * of the cgroup files ("procs" or "tasks"). We keep a list of such pidlists,
 * a pair (one each for procs, tasks) for each pid namespace that's relevant
 * to the cgroup.
 */
struct cgroup_pidlist {
	/*
	 * used to find which pidlist is wanted. doesn't change as long as
	 * this particular list stays in the list.
	*/
	struct { enum cgroup_filetype type; struct pid_namespace *ns; } key;
	/* array of xids */
	pid_t *list;
	/* how many elements the above list has */
	int length;
	/* how many files are using the current array */
	int use_count;
	/* each of these stored in a list by its cgroup */
	struct list_head links;
	/* pointer to the cgroup we belong to, for list removal purposes */
	struct cgroup *owner;
	/* protects the other fields */
	struct rw_semaphore mutex;
};

/*
 * The following two functions "fix" the issue where there are more pids
 * than kmalloc will give memory for; in such cases, we use vmalloc/vfree.
 * TODO: replace with a kernel-wide solution to this problem
 */
#define PIDLIST_TOO_LARGE(c) ((c) * sizeof(pid_t) > (PAGE_SIZE * 2))
static void *pidlist_allocate(int count)
{
	if (PIDLIST_TOO_LARGE(count))
		return vmalloc(count * sizeof(pid_t));
	else
		return kmalloc(count * sizeof(pid_t), GFP_KERNEL);
}
static void pidlist_free(void *p)
{
	if (is_vmalloc_addr(p))
		vfree(p);
	else
		kfree(p);
}

/*
 * pidlist_uniq - given a kmalloc()ed list, strip out all duplicate entries
 * Returns the number of unique elements.
 */
static int pidlist_uniq(pid_t *list, int length)
{
	int src, dest = 1;

	/*
	 * we presume the 0th element is unique, so i starts at 1. trivial
	 * edge cases first; no work needs to be done for either
	 */
	if (length == 0 || length == 1)
		return length;
	/* src and dest walk down the list; dest counts unique elements */
	for (src = 1; src < length; src++) {
		/* find next unique element */
		while (list[src] == list[src-1]) {
			src++;
			if (src == length)
				goto after;
		}
		/* dest always points to where the next unique element goes */
		list[dest] = list[src];
		dest++;
	}
after:
	return dest;
}

static int cmppid(const void *a, const void *b)
{
	return *(pid_t *)a - *(pid_t *)b;
}

/*
 * find the appropriate pidlist for our purpose (given procs vs tasks)
 * returns with the lock on that pidlist already held, and takes care
 * of the use count, or returns NULL with no locks held if we're out of
 * memory.
 */
static struct cgroup_pidlist *cgroup_pidlist_find(struct cgroup *cgrp,
						  enum cgroup_filetype type)
{
	struct cgroup_pidlist *l;
	/* don't need task_nsproxy() if we're looking at ourself */
	struct pid_namespace *ns = task_active_pid_ns(current);

	/*
	 * We can't drop the pidlist_mutex before taking the l->mutex in case
	 * the last ref-holder is trying to remove l from the list at the same
	 * time. Holding the pidlist_mutex precludes somebody taking whichever
	 * list we find out from under us - compare release_pid_array().
	 */
	mutex_lock(&cgrp->pidlist_mutex);
	list_for_each_entry(l, &cgrp->pidlists, links) {
		if (l->key.type == type && l->key.ns == ns) {
			/* make sure l doesn't vanish out from under us */
			down_write(&l->mutex);
			mutex_unlock(&cgrp->pidlist_mutex);
			return l;
		}
	}
	/* entry not found; create a new one */
	l = kzalloc(sizeof(struct cgroup_pidlist), GFP_KERNEL);
	if (!l) {
		mutex_unlock(&cgrp->pidlist_mutex);
		return l;
	}
	init_rwsem(&l->mutex);
	down_write(&l->mutex);
	l->key.type = type;
	l->key.ns = get_pid_ns(ns);
	l->owner = cgrp;
	list_add(&l->links, &cgrp->pidlists);
	mutex_unlock(&cgrp->pidlist_mutex);
	return l;
}

/*
 * Load a cgroup's pidarray with either procs' tgids or tasks' pids
 */
static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type,
			      struct cgroup_pidlist **lp)
{
	pid_t *array;
	int length;
	int pid, n = 0; /* used for populating the array */
	struct cgroup_iter it;
	struct task_struct *tsk;
	struct cgroup_pidlist *l;

	/*
	 * If cgroup gets more users after we read count, we won't have
	 * enough space - tough.  This race is indistinguishable to the
	 * caller from the case that the additional cgroup users didn't
	 * show up until sometime later on.
	 */
	length = cgroup_task_count(cgrp);
	array = pidlist_allocate(length);
	if (!array)
		return -ENOMEM;
	/* now, populate the array */
	cgroup_iter_start(cgrp, &it);
	while ((tsk = cgroup_iter_next(cgrp, &it))) {
		if (unlikely(n == length))
			break;
		/* get tgid or pid for procs or tasks file respectively */
		if (type == CGROUP_FILE_PROCS)
			pid = task_tgid_vnr(tsk);
		else
			pid = task_pid_vnr(tsk);
		if (pid > 0) /* make sure to only use valid results */
			array[n++] = pid;
	}
	cgroup_iter_end(cgrp, &it);
	length = n;
	/* now sort & (if procs) strip out duplicates */
	sort(array, length, sizeof(pid_t), cmppid, NULL);
	if (type == CGROUP_FILE_PROCS)
		length = pidlist_uniq(array, length);
	l = cgroup_pidlist_find(cgrp, type);
	if (!l) {
		pidlist_free(array);
		return -ENOMEM;
	}
	/* store array, freeing old if necessary - lock already held */
	pidlist_free(l->list);
	l->list = array;
	l->length = length;
	l->use_count++;
	up_write(&l->mutex);
	*lp = l;
	return 0;
}

/**
 * cgroupstats_build - build and fill cgroupstats
 * @stats: cgroupstats to fill information into
 * @dentry: A dentry entry belonging to the cgroup for which stats have
 * been requested.
 *
 * Build and fill cgroupstats so that taskstats can export it to user
 * space.
 */
int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
{
	int ret = -EINVAL;
	struct cgroup *cgrp;
	struct cgroup_iter it;
	struct task_struct *tsk;

	/*
	 * Validate dentry by checking the superblock operations,
	 * and make sure it's a directory.
	 */
	if (dentry->d_sb->s_op != &cgroup_ops ||
	    !S_ISDIR(dentry->d_inode->i_mode))
		 goto err;

	ret = 0;
	cgrp = dentry->d_fsdata;

	cgroup_iter_start(cgrp, &it);
	while ((tsk = cgroup_iter_next(cgrp, &it))) {
		switch (tsk->state) {
		case TASK_RUNNING:
			stats->nr_running++;
			break;
		case TASK_INTERRUPTIBLE:
			stats->nr_sleeping++;
			break;
		case TASK_UNINTERRUPTIBLE:
			stats->nr_uninterruptible++;
			break;
		case TASK_STOPPED:
			stats->nr_stopped++;
			break;
		default:
			if (delayacct_is_task_waiting_on_io(tsk))
				stats->nr_io_wait++;
			break;
		}
	}
	cgroup_iter_end(cgrp, &it);

err:
	return ret;
}


/*
 * seq_file methods for the tasks/procs files. The seq_file position is the
 * next pid to display; the seq_file iterator is a pointer to the pid
 * in the cgroup->l->list array.
 */

static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos)
{
	/*
	 * Initially we receive a position value that corresponds to
	 * one more than the last pid shown (or 0 on the first call or
	 * after a seek to the start). Use a binary-search to find the
	 * next pid to display, if any
	 */
	struct cgroup_pidlist *l = s->private;
	int index = 0, pid = *pos;
	int *iter;

	down_read(&l->mutex);
	if (pid) {
		int end = l->length;

		while (index < end) {
			int mid = (index + end) / 2;
			if (l->list[mid] == pid) {
				index = mid;
				break;
			} else if (l->list[mid] <= pid)
				index = mid + 1;
			else
				end = mid;
		}
	}
	/* If we're off the end of the array, we're done */
	if (index >= l->length)
		return NULL;
	/* Update the abstract position to be the actual pid that we found */
	iter = l->list + index;
	*pos = *iter;
	return iter;
}

static void cgroup_pidlist_stop(struct seq_file *s, void *v)
{
	struct cgroup_pidlist *l = s->private;
	up_read(&l->mutex);
}

static void *cgroup_pidlist_next(struct seq_file *s, void *v, loff_t *pos)
{
	struct cgroup_pidlist *l = s->private;
	pid_t *p = v;
	pid_t *end = l->list + l->length;
	/*
	 * Advance to the next pid in the array. If this goes off the
	 * end, we're done
	 */
	p++;
	if (p >= end) {
		return NULL;
	} else {
		*pos = *p;
		return p;
	}
}

static int cgroup_pidlist_show(struct seq_file *s, void *v)
{
	return seq_printf(s, "%d\n", *(int *)v);
}

/*
 * seq_operations functions for iterating on pidlists through seq_file -
 * independent of whether it's tasks or procs
 */
static const struct seq_operations cgroup_pidlist_seq_operations = {
	.start = cgroup_pidlist_start,
	.stop = cgroup_pidlist_stop,
	.next = cgroup_pidlist_next,
	.show = cgroup_pidlist_show,
};

static void cgroup_release_pid_array(struct cgroup_pidlist *l)
{
	/*
	 * the case where we're the last user of this particular pidlist will
	 * have us remove it from the cgroup's list, which entails taking the
	 * mutex. since in pidlist_find the pidlist->lock depends on cgroup->
	 * pidlist_mutex, we have to take pidlist_mutex first.
	 */
	mutex_lock(&l->owner->pidlist_mutex);
	down_write(&l->mutex);
	BUG_ON(!l->use_count);
	if (!--l->use_count) {
		/* we're the last user if refcount is 0; remove and free */
		list_del(&l->links);
		mutex_unlock(&l->owner->pidlist_mutex);
		pidlist_free(l->list);
		put_pid_ns(l->key.ns);
		up_write(&l->mutex);
		kfree(l);
		return;
	}
	mutex_unlock(&l->owner->pidlist_mutex);
	up_write(&l->mutex);
}

static int cgroup_pidlist_release(struct inode *inode, struct file *file)
{
	struct cgroup_pidlist *l;
	if (!(file->f_mode & FMODE_READ))
		return 0;
	/*
	 * the seq_file will only be initialized if the file was opened for
	 * reading; hence we check if it's not null only in that case.
	 */
	l = ((struct seq_file *)file->private_data)->private;
	cgroup_release_pid_array(l);
	return seq_release(inode, file);
}

static const struct file_operations cgroup_pidlist_operations = {
	.read = seq_read,
	.llseek = seq_lseek,
	.write = cgroup_file_write,
	.release = cgroup_pidlist_release,
};

/*
 * The following functions handle opens on a file that displays a pidlist
 * (tasks or procs). Prepare an array of the process/thread IDs of whoever's
 * in the cgroup.
 */
/* helper function for the two below it */
static int cgroup_pidlist_open(struct file *file, enum cgroup_filetype type)
{
	struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
	struct cgroup_pidlist *l;
	int retval;

	/* Nothing to do for write-only files */
	if (!(file->f_mode & FMODE_READ))
		return 0;

	/* have the array populated */
	retval = pidlist_array_load(cgrp, type, &l);
	if (retval)
		return retval;
	/* configure file information */
	file->f_op = &cgroup_pidlist_operations;

	retval = seq_open(file, &cgroup_pidlist_seq_operations);
	if (retval) {
		cgroup_release_pid_array(l);
		return retval;
	}
	((struct seq_file *)file->private_data)->private = l;
	return 0;
}
static int cgroup_tasks_open(struct inode *unused, struct file *file)
{
	return cgroup_pidlist_open(file, CGROUP_FILE_TASKS);
}
static int cgroup_procs_open(struct inode *unused, struct file *file)
{
	return cgroup_pidlist_open(file, CGROUP_FILE_PROCS);
}

static u64 cgroup_read_notify_on_release(struct cgroup *cgrp,
					    struct cftype *cft)
{
	return notify_on_release(cgrp);
}

static int cgroup_write_notify_on_release(struct cgroup *cgrp,
					  struct cftype *cft,
					  u64 val)
{
	clear_bit(CGRP_RELEASABLE, &cgrp->flags);
	if (val)
		set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
	else
		clear_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
	return 0;
}

/*
 * When dput() is called asynchronously, if umount has been done and
 * then deactivate_super() in cgroup_free_fn() kills the superblock,
 * there's a small window that vfs will see the root dentry with non-zero
 * refcnt and trigger BUG().
 *
 * That's why we hold a reference before dput() and drop it right after.
 */
static void cgroup_dput(struct cgroup *cgrp)
{
	struct super_block *sb = cgrp->root->sb;

	atomic_inc(&sb->s_active);
	dput(cgrp->dentry);
	deactivate_super(sb);
}

/*
 * Unregister event and free resources.
 *
 * Gets called from workqueue.
 */
static void cgroup_event_remove(struct work_struct *work)
{
	struct cgroup_event *event = container_of(work, struct cgroup_event,
			remove);
	struct cgroup *cgrp = event->cgrp;

	remove_wait_queue(event->wqh, &event->wait);

	event->cft->unregister_event(cgrp, event->cft, event->eventfd);

	/* Notify userspace the event is going away. */
	eventfd_signal(event->eventfd, 1);

	eventfd_ctx_put(event->eventfd);
	kfree(event);
	cgroup_dput(cgrp);
}

/*
 * Gets called on POLLHUP on eventfd when user closes it.
 *
 * Called with wqh->lock held and interrupts disabled.
 */
static int cgroup_event_wake(wait_queue_t *wait, unsigned mode,
		int sync, void *key)
{
	struct cgroup_event *event = container_of(wait,
			struct cgroup_event, wait);
	struct cgroup *cgrp = event->cgrp;
	unsigned long flags = (unsigned long)key;

	if (flags & POLLHUP) {
		/*
		 * If the event has been detached at cgroup removal, we
		 * can simply return knowing the other side will cleanup
		 * for us.
		 *
		 * We can't race against event freeing since the other
		 * side will require wqh->lock via remove_wait_queue(),
		 * which we hold.
		 */
		spin_lock(&cgrp->event_list_lock);
		if (!list_empty(&event->list)) {
			list_del_init(&event->list);
			/*
			 * We are in atomic context, but cgroup_event_remove()
			 * may sleep, so we have to call it in workqueue.
			 */
			schedule_work(&event->remove);
		}
		spin_unlock(&cgrp->event_list_lock);
	}

	return 0;
}

static void cgroup_event_ptable_queue_proc(struct file *file,
		wait_queue_head_t *wqh, poll_table *pt)
{
	struct cgroup_event *event = container_of(pt,
			struct cgroup_event, pt);

	event->wqh = wqh;
	add_wait_queue(wqh, &event->wait);
}

/*
 * Parse input and register new cgroup event handler.
 *
 * Input must be in format '<event_fd> <control_fd> <args>'.
 * Interpretation of args is defined by control file implementation.
 */
static int cgroup_write_event_control(struct cgroup *cgrp, struct cftype *cft,
				      const char *buffer)
{
	struct cgroup_event *event = NULL;
	struct cgroup *cgrp_cfile;
	unsigned int efd, cfd;
	struct file *efile = NULL;
	struct file *cfile = NULL;
	char *endp;
	int ret;

	efd = simple_strtoul(buffer, &endp, 10);
	if (*endp != ' ')
		return -EINVAL;
	buffer = endp + 1;

	cfd = simple_strtoul(buffer, &endp, 10);
	if ((*endp != ' ') && (*endp != '\0'))
		return -EINVAL;
	buffer = endp + 1;

	event = kzalloc(sizeof(*event), GFP_KERNEL);
	if (!event)
		return -ENOMEM;
	event->cgrp = cgrp;
	INIT_LIST_HEAD(&event->list);
	init_poll_funcptr(&event->pt, cgroup_event_ptable_queue_proc);
	init_waitqueue_func_entry(&event->wait, cgroup_event_wake);
	INIT_WORK(&event->remove, cgroup_event_remove);

	efile = eventfd_fget(efd);
	if (IS_ERR(efile)) {
		ret = PTR_ERR(efile);
		goto fail;
	}

	event->eventfd = eventfd_ctx_fileget(efile);
	if (IS_ERR(event->eventfd)) {
		ret = PTR_ERR(event->eventfd);
		goto fail;
	}

	cfile = fget(cfd);
	if (!cfile) {
		ret = -EBADF;
		goto fail;
	}

	/* the process need read permission on control file */
	/* AV: shouldn't we check that it's been opened for read instead? */
	ret = inode_permission(file_inode(cfile), MAY_READ);
	if (ret < 0)
		goto fail;

	event->cft = __file_cft(cfile);
	if (IS_ERR(event->cft)) {
		ret = PTR_ERR(event->cft);
		goto fail;
	}

	/*
	 * The file to be monitored must be in the same cgroup as
	 * cgroup.event_control is.
	 */
	cgrp_cfile = __d_cgrp(cfile->f_dentry->d_parent);
	if (cgrp_cfile != cgrp) {
		ret = -EINVAL;
		goto fail;
	}

	if (!event->cft->register_event || !event->cft->unregister_event) {
		ret = -EINVAL;
		goto fail;
	}

	ret = event->cft->register_event(cgrp, event->cft,
			event->eventfd, buffer);
	if (ret)
		goto fail;

	efile->f_op->poll(efile, &event->pt);

	/*
	 * Events should be removed after rmdir of cgroup directory, but before
	 * destroying subsystem state objects. Let's take reference to cgroup
	 * directory dentry to do that.
	 */
	dget(cgrp->dentry);

	spin_lock(&cgrp->event_list_lock);
	list_add(&event->list, &cgrp->event_list);
	spin_unlock(&cgrp->event_list_lock);

	fput(cfile);
	fput(efile);

	return 0;

fail:
	if (cfile)
		fput(cfile);

	if (event && event->eventfd && !IS_ERR(event->eventfd))
		eventfd_ctx_put(event->eventfd);

	if (!IS_ERR_OR_NULL(efile))
		fput(efile);

	kfree(event);

	return ret;
}

static u64 cgroup_clone_children_read(struct cgroup *cgrp,
				    struct cftype *cft)
{
	return test_bit(CGRP_CPUSET_CLONE_CHILDREN, &cgrp->flags);
}

static int cgroup_clone_children_write(struct cgroup *cgrp,
				     struct cftype *cft,
				     u64 val)
{
	if (val)
		set_bit(CGRP_CPUSET_CLONE_CHILDREN, &cgrp->flags);
	else
		clear_bit(CGRP_CPUSET_CLONE_CHILDREN, &cgrp->flags);
	return 0;
}

static struct cftype cgroup_base_files[] = {
	{
		.name = "cgroup.procs",
		.open = cgroup_procs_open,
		.write_u64 = cgroup_procs_write,
		.release = cgroup_pidlist_release,
		.mode = S_IRUGO | S_IWUSR,
	},
	{
		.name = "cgroup.event_control",
		.write_string = cgroup_write_event_control,
		.mode = S_IWUGO,
	},
	{
		.name = "cgroup.clone_children",
		.flags = CFTYPE_INSANE,
		.read_u64 = cgroup_clone_children_read,
		.write_u64 = cgroup_clone_children_write,
	},
	{
		.name = "cgroup.sane_behavior",
		.flags = CFTYPE_ONLY_ON_ROOT,
		.read_seq_string = cgroup_sane_behavior_show,
	},

	/*
	 * Historical crazy stuff.  These don't have "cgroup."  prefix and
	 * don't exist if sane_behavior.  If you're depending on these, be
	 * prepared to be burned.
	 */
	{
		.name = "tasks",
		.flags = CFTYPE_INSANE,		/* use "procs" instead */
		.open = cgroup_tasks_open,
		.write_u64 = cgroup_tasks_write,
		.release = cgroup_pidlist_release,
		.mode = S_IRUGO | S_IWUSR,
	},
	{
		.name = "notify_on_release",
		.flags = CFTYPE_INSANE,
		.read_u64 = cgroup_read_notify_on_release,
		.write_u64 = cgroup_write_notify_on_release,
	},
	{
		.name = "release_agent",
		.flags = CFTYPE_INSANE | CFTYPE_ONLY_ON_ROOT,
		.read_seq_string = cgroup_release_agent_show,
		.write_string = cgroup_release_agent_write,
		.max_write_len = PATH_MAX,
	},
	{ }	/* terminate */
};

/**
 * cgroup_populate_dir - selectively creation of files in a directory
 * @cgrp: target cgroup
 * @base_files: true if the base files should be added
 * @subsys_mask: mask of the subsystem ids whose files should be added
 */
static int cgroup_populate_dir(struct cgroup *cgrp, bool base_files,
			       unsigned long subsys_mask)
{
	int err;
	struct cgroup_subsys *ss;

	if (base_files) {
		err = cgroup_addrm_files(cgrp, NULL, cgroup_base_files, true);
		if (err < 0)
			return err;
	}

	/* process cftsets of each subsystem */
	for_each_root_subsys(cgrp->root, ss) {
		struct cftype_set *set;
		if (!test_bit(ss->subsys_id, &subsys_mask))
			continue;

		list_for_each_entry(set, &ss->cftsets, node)
			cgroup_addrm_files(cgrp, ss, set->cfts, true);
	}

	/* This cgroup is ready now */
	for_each_root_subsys(cgrp->root, ss) {
		struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
		struct css_id *id = rcu_dereference_protected(css->id, true);

		/*
		 * Update id->css pointer and make this css visible from
		 * CSS ID functions. This pointer will be dereferened
		 * from RCU-read-side without locks.
		 */
		if (id)
			rcu_assign_pointer(id->css, css);
	}

	return 0;
}

static void css_dput_fn(struct work_struct *work)
{
	struct cgroup_subsys_state *css =
		container_of(work, struct cgroup_subsys_state, dput_work);

	cgroup_dput(css->cgroup);
}

static void css_release(struct percpu_ref *ref)
{
	struct cgroup_subsys_state *css =
		container_of(ref, struct cgroup_subsys_state, refcnt);

	schedule_work(&css->dput_work);
}

static void init_cgroup_css(struct cgroup_subsys_state *css,
			       struct cgroup_subsys *ss,
			       struct cgroup *cgrp)
{
	css->cgroup = cgrp;
	css->flags = 0;
	css->id = NULL;
	if (cgrp == cgroup_dummy_top)
		css->flags |= CSS_ROOT;
	BUG_ON(cgrp->subsys[ss->subsys_id]);
	cgrp->subsys[ss->subsys_id] = css;

	/*
	 * css holds an extra ref to @cgrp->dentry which is put on the last
	 * css_put().  dput() requires process context, which css_put() may
	 * be called without.  @css->dput_work will be used to invoke
	 * dput() asynchronously from css_put().
	 */
	INIT_WORK(&css->dput_work, css_dput_fn);
}

/* invoke ->post_create() on a new CSS and mark it online if successful */
static int online_css(struct cgroup_subsys *ss, struct cgroup *cgrp)
{
	int ret = 0;

	lockdep_assert_held(&cgroup_mutex);

	if (ss->css_online)
		ret = ss->css_online(cgrp);
	if (!ret)
		cgrp->subsys[ss->subsys_id]->flags |= CSS_ONLINE;
	return ret;
}

/* if the CSS is online, invoke ->pre_destory() on it and mark it offline */
static void offline_css(struct cgroup_subsys *ss, struct cgroup *cgrp)
	__releases(&cgroup_mutex) __acquires(&cgroup_mutex)
{
	struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];

	lockdep_assert_held(&cgroup_mutex);

	if (!(css->flags & CSS_ONLINE))
		return;

	if (ss->css_offline)
		ss->css_offline(cgrp);

	cgrp->subsys[ss->subsys_id]->flags &= ~CSS_ONLINE;
}

/*
 * cgroup_create - create a cgroup
 * @parent: cgroup that will be parent of the new cgroup
 * @dentry: dentry of the new cgroup
 * @mode: mode to set on new inode
 *
 * Must be called with the mutex on the parent inode held
 */
static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
			     umode_t mode)
{
	struct cgroup *cgrp;
	struct cgroup_name *name;
	struct cgroupfs_root *root = parent->root;
	int err = 0;
	struct cgroup_subsys *ss;
	struct super_block *sb = root->sb;

	/* allocate the cgroup and its ID, 0 is reserved for the root */
	cgrp = kzalloc(sizeof(*cgrp), GFP_KERNEL);
	if (!cgrp)
		return -ENOMEM;

	name = cgroup_alloc_name(dentry);
	if (!name)
		goto err_free_cgrp;
	rcu_assign_pointer(cgrp->name, name);

	cgrp->id = ida_simple_get(&root->cgroup_ida, 1, 0, GFP_KERNEL);
	if (cgrp->id < 0)
		goto err_free_name;

	/*
	 * Only live parents can have children.  Note that the liveliness
	 * check isn't strictly necessary because cgroup_mkdir() and
	 * cgroup_rmdir() are fully synchronized by i_mutex; however, do it
	 * anyway so that locking is contained inside cgroup proper and we
	 * don't get nasty surprises if we ever grow another caller.
	 */
	if (!cgroup_lock_live_group(parent)) {
		err = -ENODEV;
		goto err_free_id;
	}

	/* Grab a reference on the superblock so the hierarchy doesn't
	 * get deleted on unmount if there are child cgroups.  This
	 * can be done outside cgroup_mutex, since the sb can't
	 * disappear while someone has an open control file on the
	 * fs */
	atomic_inc(&sb->s_active);

	init_cgroup_housekeeping(cgrp);

	dentry->d_fsdata = cgrp;
	cgrp->dentry = dentry;

	cgrp->parent = parent;
	cgrp->root = parent->root;

	if (notify_on_release(parent))
		set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);

	if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &parent->flags))
		set_bit(CGRP_CPUSET_CLONE_CHILDREN, &cgrp->flags);

	for_each_root_subsys(root, ss) {
		struct cgroup_subsys_state *css;

		css = ss->css_alloc(cgrp);
		if (IS_ERR(css)) {
			err = PTR_ERR(css);
			goto err_free_all;
		}

		err = percpu_ref_init(&css->refcnt, css_release);
		if (err) {
			ss->css_free(cgrp);
			goto err_free_all;
		}

		init_cgroup_css(css, ss, cgrp);

		if (ss->use_id) {
			err = alloc_css_id(ss, parent, cgrp);
			if (err)
				goto err_free_all;
		}
	}

	/*
	 * Create directory.  cgroup_create_file() returns with the new
	 * directory locked on success so that it can be populated without
	 * dropping cgroup_mutex.
	 */
	err = cgroup_create_file(dentry, S_IFDIR | mode, sb);
	if (err < 0)
		goto err_free_all;
	lockdep_assert_held(&dentry->d_inode->i_mutex);

	cgrp->serial_nr = cgroup_serial_nr_next++;

	/* allocation complete, commit to creation */
	list_add_tail_rcu(&cgrp->sibling, &cgrp->parent->children);
	root->number_of_cgroups++;

	/* each css holds a ref to the cgroup's dentry */
	for_each_root_subsys(root, ss)
		dget(dentry);

	/* hold a ref to the parent's dentry */
	dget(parent->dentry);

	/* creation succeeded, notify subsystems */
	for_each_root_subsys(root, ss) {
		err = online_css(ss, cgrp);
		if (err)
			goto err_destroy;

		if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
		    parent->parent) {
			pr_warning("cgroup: %s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n",
				   current->comm, current->pid, ss->name);
			if (!strcmp(ss->name, "memory"))
				pr_warning("cgroup: \"memory\" requires setting use_hierarchy to 1 on the root.\n");
			ss->warned_broken_hierarchy = true;
		}
	}

	err = cgroup_populate_dir(cgrp, true, root->subsys_mask);
	if (err)
		goto err_destroy;

	mutex_unlock(&cgroup_mutex);
	mutex_unlock(&cgrp->dentry->d_inode->i_mutex);

	return 0;

err_free_all:
	for_each_root_subsys(root, ss) {
		struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];

		if (css) {
			percpu_ref_cancel_init(&css->refcnt);
			ss->css_free(cgrp);
		}
	}
	mutex_unlock(&cgroup_mutex);
	/* Release the reference count that we took on the superblock */
	deactivate_super(sb);
err_free_id:
	ida_simple_remove(&root->cgroup_ida, cgrp->id);
err_free_name:
	kfree(rcu_dereference_raw(cgrp->name));
err_free_cgrp:
	kfree(cgrp);
	return err;

err_destroy:
	cgroup_destroy_locked(cgrp);
	mutex_unlock(&cgroup_mutex);
	mutex_unlock(&dentry->d_inode->i_mutex);
	return err;
}

static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
{
	struct cgroup *c_parent = dentry->d_parent->d_fsdata;

	/* the vfs holds inode->i_mutex already */
	return cgroup_create(c_parent, dentry, mode | S_IFDIR);
}

static void cgroup_css_killed(struct cgroup *cgrp)
{
	if (!atomic_dec_and_test(&cgrp->css_kill_cnt))
		return;

	/* percpu ref's of all css's are killed, kick off the next step */
	INIT_WORK(&cgrp->destroy_work, cgroup_offline_fn);
	schedule_work(&cgrp->destroy_work);
}

static void css_ref_killed_fn(struct percpu_ref *ref)
{
	struct cgroup_subsys_state *css =
		container_of(ref, struct cgroup_subsys_state, refcnt);

	cgroup_css_killed(css->cgroup);
}

/**
 * cgroup_destroy_locked - the first stage of cgroup destruction
 * @cgrp: cgroup to be destroyed
 *
 * css's make use of percpu refcnts whose killing latency shouldn't be
 * exposed to userland and are RCU protected.  Also, cgroup core needs to
 * guarantee that css_tryget() won't succeed by the time ->css_offline() is
 * invoked.  To satisfy all the requirements, destruction is implemented in
 * the following two steps.
 *
 * s1. Verify @cgrp can be destroyed and mark it dying.  Remove all
 *     userland visible parts and start killing the percpu refcnts of
 *     css's.  Set up so that the next stage will be kicked off once all
 *     the percpu refcnts are confirmed to be killed.
 *
 * s2. Invoke ->css_offline(), mark the cgroup dead and proceed with the
 *     rest of destruction.  Once all cgroup references are gone, the
 *     cgroup is RCU-freed.
 *
 * This function implements s1.  After this step, @cgrp is gone as far as
 * the userland is concerned and a new cgroup with the same name may be
 * created.  As cgroup doesn't care about the names internally, this
 * doesn't cause any problem.
 */
static int cgroup_destroy_locked(struct cgroup *cgrp)
	__releases(&cgroup_mutex) __acquires(&cgroup_mutex)
{
	struct dentry *d = cgrp->dentry;
	struct cgroup_event *event, *tmp;
	struct cgroup_subsys *ss;
	struct cgroup *child;
	bool empty;

	lockdep_assert_held(&d->d_inode->i_mutex);
	lockdep_assert_held(&cgroup_mutex);

	/*
	 * css_set_lock synchronizes access to ->cset_links and prevents
	 * @cgrp from being removed while __put_css_set() is in progress.
	 */
	read_lock(&css_set_lock);
	empty = list_empty(&cgrp->cset_links);
	read_unlock(&css_set_lock);
	if (!empty)
		return -EBUSY;

	/*
	 * Make sure there's no live children.  We can't test ->children
	 * emptiness as dead children linger on it while being destroyed;
	 * otherwise, "rmdir parent/child parent" may fail with -EBUSY.
	 */
	empty = true;
	rcu_read_lock();
	list_for_each_entry_rcu(child, &cgrp->children, sibling) {
		empty = cgroup_is_dead(child);
		if (!empty)
			break;
	}
	rcu_read_unlock();
	if (!empty)
		return -EBUSY;

	/*
	 * Block new css_tryget() by killing css refcnts.  cgroup core
	 * guarantees that, by the time ->css_offline() is invoked, no new
	 * css reference will be given out via css_tryget().  We can't
	 * simply call percpu_ref_kill() and proceed to offlining css's
	 * because percpu_ref_kill() doesn't guarantee that the ref is seen
	 * as killed on all CPUs on return.
	 *
	 * Use percpu_ref_kill_and_confirm() to get notifications as each
	 * css is confirmed to be seen as killed on all CPUs.  The
	 * notification callback keeps track of the number of css's to be
	 * killed and schedules cgroup_offline_fn() to perform the rest of
	 * destruction once the percpu refs of all css's are confirmed to
	 * be killed.
	 */
	atomic_set(&cgrp->css_kill_cnt, 1);
	for_each_root_subsys(cgrp->root, ss) {
		struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];

		/*
		 * Killing would put the base ref, but we need to keep it
		 * alive until after ->css_offline.
		 */
		percpu_ref_get(&css->refcnt);

		atomic_inc(&cgrp->css_kill_cnt);
		percpu_ref_kill_and_confirm(&css->refcnt, css_ref_killed_fn);
	}
	cgroup_css_killed(cgrp);

	/*
	 * Mark @cgrp dead.  This prevents further task migration and child
	 * creation by disabling cgroup_lock_live_group().  Note that
	 * CGRP_DEAD assertion is depended upon by cgroup_next_sibling() to
	 * resume iteration after dropping RCU read lock.  See
	 * cgroup_next_sibling() for details.
	 */
	set_bit(CGRP_DEAD, &cgrp->flags);

	/* CGRP_DEAD is set, remove from ->release_list for the last time */
	raw_spin_lock(&release_list_lock);
	if (!list_empty(&cgrp->release_list))
		list_del_init(&cgrp->release_list);
	raw_spin_unlock(&release_list_lock);

	/*
	 * Remove @cgrp directory.  The removal puts the base ref but we
	 * aren't quite done with @cgrp yet, so hold onto it.
	 */
	dget(d);
	cgroup_d_remove_dir(d);

	/*
	 * Unregister events and notify userspace.
	 * Notify userspace about cgroup removing only after rmdir of cgroup
	 * directory to avoid race between userspace and kernelspace.
	 */
	spin_lock(&cgrp->event_list_lock);
	list_for_each_entry_safe(event, tmp, &cgrp->event_list, list) {
		list_del_init(&event->list);
		schedule_work(&event->remove);
	}
	spin_unlock(&cgrp->event_list_lock);

	return 0;
};

/**
 * cgroup_offline_fn - the second step of cgroup destruction
 * @work: cgroup->destroy_free_work
 *
 * This function is invoked from a work item for a cgroup which is being
 * destroyed after the percpu refcnts of all css's are guaranteed to be
 * seen as killed on all CPUs, and performs the rest of destruction.  This
 * is the second step of destruction described in the comment above
 * cgroup_destroy_locked().
 */
static void cgroup_offline_fn(struct work_struct *work)
{
	struct cgroup *cgrp = container_of(work, struct cgroup, destroy_work);
	struct cgroup *parent = cgrp->parent;
	struct dentry *d = cgrp->dentry;
	struct cgroup_subsys *ss;

	mutex_lock(&cgroup_mutex);

	/*
	 * css_tryget() is guaranteed to fail now.  Tell subsystems to
	 * initate destruction.
	 */
	for_each_root_subsys(cgrp->root, ss)
		offline_css(ss, cgrp);

	/*
	 * Put the css refs from cgroup_destroy_locked().  Each css holds
	 * an extra reference to the cgroup's dentry and cgroup removal
	 * proceeds regardless of css refs.  On the last put of each css,
	 * whenever that may be, the extra dentry ref is put so that dentry
	 * destruction happens only after all css's are released.
	 */
	for_each_root_subsys(cgrp->root, ss)
		css_put(cgrp->subsys[ss->subsys_id]);

	/* delete this cgroup from parent->children */
	list_del_rcu(&cgrp->sibling);

	dput(d);

	set_bit(CGRP_RELEASABLE, &parent->flags);
	check_for_release(parent);

	mutex_unlock(&cgroup_mutex);
}

static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
{
	int ret;

	mutex_lock(&cgroup_mutex);
	ret = cgroup_destroy_locked(dentry->d_fsdata);
	mutex_unlock(&cgroup_mutex);

	return ret;
}

static void __init_or_module cgroup_init_cftsets(struct cgroup_subsys *ss)
{
	INIT_LIST_HEAD(&ss->cftsets);

	/*
	 * base_cftset is embedded in subsys itself, no need to worry about
	 * deregistration.
	 */
	if (ss->base_cftypes) {
		ss->base_cftset.cfts = ss->base_cftypes;
		list_add_tail(&ss->base_cftset.node, &ss->cftsets);
	}
}

static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
{
	struct cgroup_subsys_state *css;

	printk(KERN_INFO "Initializing cgroup subsys %s\n", ss->name);

	mutex_lock(&cgroup_mutex);

	/* init base cftset */
	cgroup_init_cftsets(ss);

	/* Create the top cgroup state for this subsystem */
	list_add(&ss->sibling, &cgroup_dummy_root.subsys_list);
	ss->root = &cgroup_dummy_root;
	css = ss->css_alloc(cgroup_dummy_top);
	/* We don't handle early failures gracefully */
	BUG_ON(IS_ERR(css));
	init_cgroup_css(css, ss, cgroup_dummy_top);

	/* Update the init_css_set to contain a subsys
	 * pointer to this state - since the subsystem is
	 * newly registered, all tasks and hence the
	 * init_css_set is in the subsystem's top cgroup. */
	init_css_set.subsys[ss->subsys_id] = css;

	need_forkexit_callback |= ss->fork || ss->exit;

	/* At system boot, before all subsystems have been
	 * registered, no tasks have been forked, so we don't
	 * need to invoke fork callbacks here. */
	BUG_ON(!list_empty(&init_task.tasks));

	BUG_ON(online_css(ss, cgroup_dummy_top));

	mutex_unlock(&cgroup_mutex);

	/* this function shouldn't be used with modular subsystems, since they
	 * need to register a subsys_id, among other things */
	BUG_ON(ss->module);
}

/**
 * cgroup_load_subsys: load and register a modular subsystem at runtime
 * @ss: the subsystem to load
 *
 * This function should be called in a modular subsystem's initcall. If the
 * subsystem is built as a module, it will be assigned a new subsys_id and set
 * up for use. If the subsystem is built-in anyway, work is delegated to the
 * simpler cgroup_init_subsys.
 */
int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)
{
	struct cgroup_subsys_state *css;
	int i, ret;
	struct hlist_node *tmp;
	struct css_set *cset;
	unsigned long key;

	/* check name and function validity */
	if (ss->name == NULL || strlen(ss->name) > MAX_CGROUP_TYPE_NAMELEN ||
	    ss->css_alloc == NULL || ss->css_free == NULL)
		return -EINVAL;

	/*
	 * we don't support callbacks in modular subsystems. this check is
	 * before the ss->module check for consistency; a subsystem that could
	 * be a module should still have no callbacks even if the user isn't
	 * compiling it as one.
	 */
	if (ss->fork || ss->exit)
		return -EINVAL;

	/*
	 * an optionally modular subsystem is built-in: we want to do nothing,
	 * since cgroup_init_subsys will have already taken care of it.
	 */
	if (ss->module == NULL) {
		/* a sanity check */
		BUG_ON(cgroup_subsys[ss->subsys_id] != ss);
		return 0;
	}

	/* init base cftset */
	cgroup_init_cftsets(ss);

	mutex_lock(&cgroup_mutex);
	cgroup_subsys[ss->subsys_id] = ss;

	/*
	 * no ss->css_alloc seems to need anything important in the ss
	 * struct, so this can happen first (i.e. before the dummy root
	 * attachment).
	 */
	css = ss->css_alloc(cgroup_dummy_top);
	if (IS_ERR(css)) {
		/* failure case - need to deassign the cgroup_subsys[] slot. */
		cgroup_subsys[ss->subsys_id] = NULL;
		mutex_unlock(&cgroup_mutex);
		return PTR_ERR(css);
	}

	list_add(&ss->sibling, &cgroup_dummy_root.subsys_list);
	ss->root = &cgroup_dummy_root;

	/* our new subsystem will be attached to the dummy hierarchy. */
	init_cgroup_css(css, ss, cgroup_dummy_top);
	/* init_idr must be after init_cgroup_css because it sets css->id. */
	if (ss->use_id) {
		ret = cgroup_init_idr(ss, css);
		if (ret)
			goto err_unload;
	}

	/*
	 * Now we need to entangle the css into the existing css_sets. unlike
	 * in cgroup_init_subsys, there are now multiple css_sets, so each one
	 * will need a new pointer to it; done by iterating the css_set_table.
	 * furthermore, modifying the existing css_sets will corrupt the hash
	 * table state, so each changed css_set will need its hash recomputed.
	 * this is all done under the css_set_lock.
	 */
	write_lock(&css_set_lock);
	hash_for_each_safe(css_set_table, i, tmp, cset, hlist) {
		/* skip entries that we already rehashed */
		if (cset->subsys[ss->subsys_id])
			continue;
		/* remove existing entry */
		hash_del(&cset->hlist);
		/* set new value */
		cset->subsys[ss->subsys_id] = css;
		/* recompute hash and restore entry */
		key = css_set_hash(cset->subsys);
		hash_add(css_set_table, &cset->hlist, key);
	}
	write_unlock(&css_set_lock);

	ret = online_css(ss, cgroup_dummy_top);
	if (ret)
		goto err_unload;

	/* success! */
	mutex_unlock(&cgroup_mutex);
	return 0;

err_unload:
	mutex_unlock(&cgroup_mutex);
	/* @ss can't be mounted here as try_module_get() would fail */
	cgroup_unload_subsys(ss);
	return ret;
}
EXPORT_SYMBOL_GPL(cgroup_load_subsys);

/**
 * cgroup_unload_subsys: unload a modular subsystem
 * @ss: the subsystem to unload
 *
 * This function should be called in a modular subsystem's exitcall. When this
 * function is invoked, the refcount on the subsystem's module will be 0, so
 * the subsystem will not be attached to any hierarchy.
 */
void cgroup_unload_subsys(struct cgroup_subsys *ss)
{
	struct cgrp_cset_link *link;

	BUG_ON(ss->module == NULL);

	/*
	 * we shouldn't be called if the subsystem is in use, and the use of
	 * try_module_get in parse_cgroupfs_options should ensure that it
	 * doesn't start being used while we're killing it off.
	 */
	BUG_ON(ss->root != &cgroup_dummy_root);

	mutex_lock(&cgroup_mutex);

	offline_css(ss, cgroup_dummy_top);

	if (ss->use_id)
		idr_destroy(&ss->idr);

	/* deassign the subsys_id */
	cgroup_subsys[ss->subsys_id] = NULL;

	/* remove subsystem from the dummy root's list of subsystems */
	list_del_init(&ss->sibling);

	/*
	 * disentangle the css from all css_sets attached to the dummy
	 * top. as in loading, we need to pay our respects to the hashtable
	 * gods.
	 */
	write_lock(&css_set_lock);
	list_for_each_entry(link, &cgroup_dummy_top->cset_links, cset_link) {
		struct css_set *cset = link->cset;
		unsigned long key;

		hash_del(&cset->hlist);
		cset->subsys[ss->subsys_id] = NULL;
		key = css_set_hash(cset->subsys);
		hash_add(css_set_table, &cset->hlist, key);
	}
	write_unlock(&css_set_lock);

	/*
	 * remove subsystem's css from the cgroup_dummy_top and free it -
	 * need to free before marking as null because ss->css_free needs
	 * the cgrp->subsys pointer to find their state. note that this
	 * also takes care of freeing the css_id.
	 */
	ss->css_free(cgroup_dummy_top);
	cgroup_dummy_top->subsys[ss->subsys_id] = NULL;

	mutex_unlock(&cgroup_mutex);
}
EXPORT_SYMBOL_GPL(cgroup_unload_subsys);

/**
 * cgroup_init_early - cgroup initialization at system boot
 *
 * Initialize cgroups at system boot, and initialize any
 * subsystems that request early init.
 */
int __init cgroup_init_early(void)
{
	struct cgroup_subsys *ss;
	int i;

	atomic_set(&init_css_set.refcount, 1);
	INIT_LIST_HEAD(&init_css_set.cgrp_links);
	INIT_LIST_HEAD(&init_css_set.tasks);
	INIT_HLIST_NODE(&init_css_set.hlist);
	css_set_count = 1;
	init_cgroup_root(&cgroup_dummy_root);
	cgroup_root_count = 1;
	RCU_INIT_POINTER(init_task.cgroups, &init_css_set);

	init_cgrp_cset_link.cset = &init_css_set;
	init_cgrp_cset_link.cgrp = cgroup_dummy_top;
	list_add(&init_cgrp_cset_link.cset_link, &cgroup_dummy_top->cset_links);
	list_add(&init_cgrp_cset_link.cgrp_link, &init_css_set.cgrp_links);

	/* at bootup time, we don't worry about modular subsystems */
	for_each_builtin_subsys(ss, i) {
		BUG_ON(!ss->name);
		BUG_ON(strlen(ss->name) > MAX_CGROUP_TYPE_NAMELEN);
		BUG_ON(!ss->css_alloc);
		BUG_ON(!ss->css_free);
		if (ss->subsys_id != i) {
			printk(KERN_ERR "cgroup: Subsys %s id == %d\n",
			       ss->name, ss->subsys_id);
			BUG();
		}

		if (ss->early_init)
			cgroup_init_subsys(ss);
	}
	return 0;
}

/**
 * cgroup_init - cgroup initialization
 *
 * Register cgroup filesystem and /proc file, and initialize
 * any subsystems that didn't request early init.
 */
int __init cgroup_init(void)
{
	struct cgroup_subsys *ss;
	unsigned long key;
	int i, err;

	err = bdi_init(&cgroup_backing_dev_info);
	if (err)
		return err;

	for_each_builtin_subsys(ss, i) {
		if (!ss->early_init)
			cgroup_init_subsys(ss);
		if (ss->use_id)
			cgroup_init_idr(ss, init_css_set.subsys[ss->subsys_id]);
	}

	/* allocate id for the dummy hierarchy */
	mutex_lock(&cgroup_mutex);
	mutex_lock(&cgroup_root_mutex);

	/* Add init_css_set to the hash table */
	key = css_set_hash(init_css_set.subsys);
	hash_add(css_set_table, &init_css_set.hlist, key);

	BUG_ON(cgroup_init_root_id(&cgroup_dummy_root, 0, 1));

	mutex_unlock(&cgroup_root_mutex);
	mutex_unlock(&cgroup_mutex);

	cgroup_kobj = kobject_create_and_add("cgroup", fs_kobj);
	if (!cgroup_kobj) {
		err = -ENOMEM;
		goto out;
	}

	err = register_filesystem(&cgroup_fs_type);
	if (err < 0) {
		kobject_put(cgroup_kobj);
		goto out;
	}

	proc_create("cgroups", 0, NULL, &proc_cgroupstats_operations);

out:
	if (err)
		bdi_destroy(&cgroup_backing_dev_info);

	return err;
}

/*
 * proc_cgroup_show()
 *  - Print task's cgroup paths into seq_file, one line for each hierarchy
 *  - Used for /proc/<pid>/cgroup.
 *  - No need to task_lock(tsk) on this tsk->cgroup reference, as it
 *    doesn't really matter if tsk->cgroup changes after we read it,
 *    and we take cgroup_mutex, keeping cgroup_attach_task() from changing it
 *    anyway.  No need to check that tsk->cgroup != NULL, thanks to
 *    the_top_cgroup_hack in cgroup_exit(), which sets an exiting tasks
 *    cgroup to top_cgroup.
 */

/* TODO: Use a proper seq_file iterator */
int proc_cgroup_show(struct seq_file *m, void *v)
{
	struct pid *pid;
	struct task_struct *tsk;
	char *buf;
	int retval;
	struct cgroupfs_root *root;

	retval = -ENOMEM;
	buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
	if (!buf)
		goto out;

	retval = -ESRCH;
	pid = m->private;
	tsk = get_pid_task(pid, PIDTYPE_PID);
	if (!tsk)
		goto out_free;

	retval = 0;

	mutex_lock(&cgroup_mutex);

	for_each_active_root(root) {
		struct cgroup_subsys *ss;
		struct cgroup *cgrp;
		int count = 0;

		seq_printf(m, "%d:", root->hierarchy_id);
		for_each_root_subsys(root, ss)
			seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
		if (strlen(root->name))
			seq_printf(m, "%sname=%s", count ? "," : "",
				   root->name);
		seq_putc(m, ':');
		cgrp = task_cgroup_from_root(tsk, root);
		retval = cgroup_path(cgrp, buf, PAGE_SIZE);
		if (retval < 0)
			goto out_unlock;
		seq_puts(m, buf);
		seq_putc(m, '\n');
	}

out_unlock:
	mutex_unlock(&cgroup_mutex);
	put_task_struct(tsk);
out_free:
	kfree(buf);
out:
	return retval;
}

/* Display information about each subsystem and each hierarchy */
static int proc_cgroupstats_show(struct seq_file *m, void *v)
{
	struct cgroup_subsys *ss;
	int i;

	seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n");
	/*
	 * ideally we don't want subsystems moving around while we do this.
	 * cgroup_mutex is also necessary to guarantee an atomic snapshot of
	 * subsys/hierarchy state.
	 */
	mutex_lock(&cgroup_mutex);

	for_each_subsys(ss, i)
		seq_printf(m, "%s\t%d\t%d\t%d\n",
			   ss->name, ss->root->hierarchy_id,
			   ss->root->number_of_cgroups, !ss->disabled);

	mutex_unlock(&cgroup_mutex);
	return 0;
}

static int cgroupstats_open(struct inode *inode, struct file *file)
{
	return single_open(file, proc_cgroupstats_show, NULL);
}

static const struct file_operations proc_cgroupstats_operations = {
	.open = cgroupstats_open,
	.read = seq_read,
	.llseek = seq_lseek,
	.release = single_release,
};

/**
 * cgroup_fork - attach newly forked task to its parents cgroup.
 * @child: pointer to task_struct of forking parent process.
 *
 * Description: A task inherits its parent's cgroup at fork().
 *
 * A pointer to the shared css_set was automatically copied in
 * fork.c by dup_task_struct().  However, we ignore that copy, since
 * it was not made under the protection of RCU or cgroup_mutex, so
 * might no longer be a valid cgroup pointer.  cgroup_attach_task() might
 * have already changed current->cgroups, allowing the previously
 * referenced cgroup group to be removed and freed.
 *
 * At the point that cgroup_fork() is called, 'current' is the parent
 * task, and the passed argument 'child' points to the child task.
 */
void cgroup_fork(struct task_struct *child)
{
	task_lock(current);
	get_css_set(task_css_set(current));
	child->cgroups = current->cgroups;
	task_unlock(current);
	INIT_LIST_HEAD(&child->cg_list);
}

/**
 * cgroup_post_fork - called on a new task after adding it to the task list
 * @child: the task in question
 *
 * Adds the task to the list running through its css_set if necessary and
 * call the subsystem fork() callbacks.  Has to be after the task is
 * visible on the task list in case we race with the first call to
 * cgroup_iter_start() - to guarantee that the new task ends up on its
 * list.
 */
void cgroup_post_fork(struct task_struct *child)
{
	struct cgroup_subsys *ss;
	int i;

	/*
	 * use_task_css_set_links is set to 1 before we walk the tasklist
	 * under the tasklist_lock and we read it here after we added the child
	 * to the tasklist under the tasklist_lock as well. If the child wasn't
	 * yet in the tasklist when we walked through it from
	 * cgroup_enable_task_cg_lists(), then use_task_css_set_links value
	 * should be visible now due to the paired locking and barriers implied
	 * by LOCK/UNLOCK: it is written before the tasklist_lock unlock
	 * in cgroup_enable_task_cg_lists() and read here after the tasklist_lock
	 * lock on fork.
	 */
	if (use_task_css_set_links) {
		write_lock(&css_set_lock);
		task_lock(child);
		if (list_empty(&child->cg_list))
			list_add(&child->cg_list, &task_css_set(child)->tasks);
		task_unlock(child);
		write_unlock(&css_set_lock);
	}

	/*
	 * Call ss->fork().  This must happen after @child is linked on
	 * css_set; otherwise, @child might change state between ->fork()
	 * and addition to css_set.
	 */
	if (need_forkexit_callback) {
		/*
		 * fork/exit callbacks are supported only for builtin
		 * subsystems, and the builtin section of the subsys
		 * array is immutable, so we don't need to lock the
		 * subsys array here. On the other hand, modular section
		 * of the array can be freed at module unload, so we
		 * can't touch that.
		 */
		for_each_builtin_subsys(ss, i)
			if (ss->fork)
				ss->fork(child);
	}
}

/**
 * cgroup_exit - detach cgroup from exiting task
 * @tsk: pointer to task_struct of exiting process
 * @run_callback: run exit callbacks?
 *
 * Description: Detach cgroup from @tsk and release it.
 *
 * Note that cgroups marked notify_on_release force every task in
 * them to take the global cgroup_mutex mutex when exiting.
 * This could impact scaling on very large systems.  Be reluctant to
 * use notify_on_release cgroups where very high task exit scaling
 * is required on large systems.
 *
 * the_top_cgroup_hack:
 *
 *    Set the exiting tasks cgroup to the root cgroup (top_cgroup).
 *
 *    We call cgroup_exit() while the task is still competent to
 *    handle notify_on_release(), then leave the task attached to the
 *    root cgroup in each hierarchy for the remainder of its exit.
 *
 *    To do this properly, we would increment the reference count on
 *    top_cgroup, and near the very end of the kernel/exit.c do_exit()
 *    code we would add a second cgroup function call, to drop that
 *    reference.  This would just create an unnecessary hot spot on
 *    the top_cgroup reference count, to no avail.
 *
 *    Normally, holding a reference to a cgroup without bumping its
 *    count is unsafe.   The cgroup could go away, or someone could
 *    attach us to a different cgroup, decrementing the count on
 *    the first cgroup that we never incremented.  But in this case,
 *    top_cgroup isn't going away, and either task has PF_EXITING set,
 *    which wards off any cgroup_attach_task() attempts, or task is a failed
 *    fork, never visible to cgroup_attach_task.
 */
void cgroup_exit(struct task_struct *tsk, int run_callbacks)
{
	struct cgroup_subsys *ss;
	struct css_set *cset;
	int i;

	/*
	 * Unlink from the css_set task list if necessary.
	 * Optimistically check cg_list before taking
	 * css_set_lock
	 */
	if (!list_empty(&tsk->cg_list)) {
		write_lock(&css_set_lock);
		if (!list_empty(&tsk->cg_list))
			list_del_init(&tsk->cg_list);
		write_unlock(&css_set_lock);
	}

	/* Reassign the task to the init_css_set. */
	task_lock(tsk);
	cset = task_css_set(tsk);
	RCU_INIT_POINTER(tsk->cgroups, &init_css_set);

	if (run_callbacks && need_forkexit_callback) {
		/*
		 * fork/exit callbacks are supported only for builtin
		 * subsystems, see cgroup_post_fork() for details.
		 */
		for_each_builtin_subsys(ss, i) {
			if (ss->exit) {
				struct cgroup *old_cgrp = cset->subsys[i]->cgroup;
				struct cgroup *cgrp = task_cgroup(tsk, i);

				ss->exit(cgrp, old_cgrp, tsk);
			}
		}
	}
	task_unlock(tsk);

	put_css_set_taskexit(cset);
}

static void check_for_release(struct cgroup *cgrp)
{
	if (cgroup_is_releasable(cgrp) &&
	    list_empty(&cgrp->cset_links) && list_empty(&cgrp->children)) {
		/*
		 * Control Group is currently removeable. If it's not
		 * already queued for a userspace notification, queue
		 * it now
		 */
		int need_schedule_work = 0;

		raw_spin_lock(&release_list_lock);
		if (!cgroup_is_dead(cgrp) &&
		    list_empty(&cgrp->release_list)) {
			list_add(&cgrp->release_list, &release_list);
			need_schedule_work = 1;
		}
		raw_spin_unlock(&release_list_lock);
		if (need_schedule_work)
			schedule_work(&release_agent_work);
	}
}

/*
 * Notify userspace when a cgroup is released, by running the
 * configured release agent with the name of the cgroup (path
 * relative to the root of cgroup file system) as the argument.
 *
 * Most likely, this user command will try to rmdir this cgroup.
 *
 * This races with the possibility that some other task will be
 * attached to this cgroup before it is removed, or that some other
 * user task will 'mkdir' a child cgroup of this cgroup.  That's ok.
 * The presumed 'rmdir' will fail quietly if this cgroup is no longer
 * unused, and this cgroup will be reprieved from its death sentence,
 * to continue to serve a useful existence.  Next time it's released,
 * we will get notified again, if it still has 'notify_on_release' set.
 *
 * The final arg to call_usermodehelper() is UMH_WAIT_EXEC, which
 * means only wait until the task is successfully execve()'d.  The
 * separate release agent task is forked by call_usermodehelper(),
 * then control in this thread returns here, without waiting for the
 * release agent task.  We don't bother to wait because the caller of
 * this routine has no use for the exit status of the release agent
 * task, so no sense holding our caller up for that.
 */
static void cgroup_release_agent(struct work_struct *work)
{
	BUG_ON(work != &release_agent_work);
	mutex_lock(&cgroup_mutex);
	raw_spin_lock(&release_list_lock);
	while (!list_empty(&release_list)) {
		char *argv[3], *envp[3];
		int i;
		char *pathbuf = NULL, *agentbuf = NULL;
		struct cgroup *cgrp = list_entry(release_list.next,
						    struct cgroup,
						    release_list);
		list_del_init(&cgrp->release_list);
		raw_spin_unlock(&release_list_lock);
		pathbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
		if (!pathbuf)
			goto continue_free;
		if (cgroup_path(cgrp, pathbuf, PAGE_SIZE) < 0)
			goto continue_free;
		agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL);
		if (!agentbuf)
			goto continue_free;

		i = 0;
		argv[i++] = agentbuf;
		argv[i++] = pathbuf;
		argv[i] = NULL;

		i = 0;
		/* minimal command environment */
		envp[i++] = "HOME=/";
		envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
		envp[i] = NULL;

		/* Drop the lock while we invoke the usermode helper,
		 * since the exec could involve hitting disk and hence
		 * be a slow process */
		mutex_unlock(&cgroup_mutex);
		call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
		mutex_lock(&cgroup_mutex);
 continue_free:
		kfree(pathbuf);
		kfree(agentbuf);
		raw_spin_lock(&release_list_lock);
	}
	raw_spin_unlock(&release_list_lock);
	mutex_unlock(&cgroup_mutex);
}

static int __init cgroup_disable(char *str)
{
	struct cgroup_subsys *ss;
	char *token;
	int i;

	while ((token = strsep(&str, ",")) != NULL) {
		if (!*token)
			continue;

		/*
		 * cgroup_disable, being at boot time, can't know about
		 * module subsystems, so we don't worry about them.
		 */
		for_each_builtin_subsys(ss, i) {
			if (!strcmp(token, ss->name)) {
				ss->disabled = 1;
				printk(KERN_INFO "Disabling %s control group"
					" subsystem\n", ss->name);
				break;
			}
		}
	}
	return 1;
}
__setup("cgroup_disable=", cgroup_disable);

/*
 * Functons for CSS ID.
 */

/* to get ID other than 0, this should be called when !cgroup_is_dead() */
unsigned short css_id(struct cgroup_subsys_state *css)
{
	struct css_id *cssid;

	/*
	 * This css_id() can return correct value when somone has refcnt
	 * on this or this is under rcu_read_lock(). Once css->id is allocated,
	 * it's unchanged until freed.
	 */
	cssid = rcu_dereference_raw(css->id);

	if (cssid)
		return cssid->id;
	return 0;
}
EXPORT_SYMBOL_GPL(css_id);

/**
 *  css_is_ancestor - test "root" css is an ancestor of "child"
 * @child: the css to be tested.
 * @root: the css supporsed to be an ancestor of the child.
 *
 * Returns true if "root" is an ancestor of "child" in its hierarchy. Because
 * this function reads css->id, the caller must hold rcu_read_lock().
 * But, considering usual usage, the csses should be valid objects after test.
 * Assuming that the caller will do some action to the child if this returns
 * returns true, the caller must take "child";s reference count.
 * If "child" is valid object and this returns true, "root" is valid, too.
 */

bool css_is_ancestor(struct cgroup_subsys_state *child,
		    const struct cgroup_subsys_state *root)
{
	struct css_id *child_id;
	struct css_id *root_id;

	child_id  = rcu_dereference(child->id);
	if (!child_id)
		return false;
	root_id = rcu_dereference(root->id);
	if (!root_id)
		return false;
	if (child_id->depth < root_id->depth)
		return false;
	if (child_id->stack[root_id->depth] != root_id->id)
		return false;
	return true;
}

void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css)
{
	struct css_id *id = rcu_dereference_protected(css->id, true);

	/* When this is called before css_id initialization, id can be NULL */
	if (!id)
		return;

	BUG_ON(!ss->use_id);

	rcu_assign_pointer(id->css, NULL);
	rcu_assign_pointer(css->id, NULL);
	spin_lock(&ss->id_lock);
	idr_remove(&ss->idr, id->id);
	spin_unlock(&ss->id_lock);
	kfree_rcu(id, rcu_head);
}
EXPORT_SYMBOL_GPL(free_css_id);

/*
 * This is called by init or create(). Then, calls to this function are
 * always serialized (By cgroup_mutex() at create()).
 */

static struct css_id *get_new_cssid(struct cgroup_subsys *ss, int depth)
{
	struct css_id *newid;
	int ret, size;

	BUG_ON(!ss->use_id);

	size = sizeof(*newid) + sizeof(unsigned short) * (depth + 1);
	newid = kzalloc(size, GFP_KERNEL);
	if (!newid)
		return ERR_PTR(-ENOMEM);

	idr_preload(GFP_KERNEL);
	spin_lock(&ss->id_lock);
	/* Don't use 0. allocates an ID of 1-65535 */
	ret = idr_alloc(&ss->idr, newid, 1, CSS_ID_MAX + 1, GFP_NOWAIT);
	spin_unlock(&ss->id_lock);
	idr_preload_end();

	/* Returns error when there are no free spaces for new ID.*/
	if (ret < 0)
		goto err_out;

	newid->id = ret;
	newid->depth = depth;
	return newid;
err_out:
	kfree(newid);
	return ERR_PTR(ret);

}

static int __init_or_module cgroup_init_idr(struct cgroup_subsys *ss,
					    struct cgroup_subsys_state *rootcss)
{
	struct css_id *newid;

	spin_lock_init(&ss->id_lock);
	idr_init(&ss->idr);

	newid = get_new_cssid(ss, 0);
	if (IS_ERR(newid))
		return PTR_ERR(newid);

	newid->stack[0] = newid->id;
	RCU_INIT_POINTER(newid->css, rootcss);
	RCU_INIT_POINTER(rootcss->id, newid);
	return 0;
}

static int alloc_css_id(struct cgroup_subsys *ss, struct cgroup *parent,
			struct cgroup *child)
{
	int subsys_id, i, depth = 0;
	struct cgroup_subsys_state *parent_css, *child_css;
	struct css_id *child_id, *parent_id;

	subsys_id = ss->subsys_id;
	parent_css = parent->subsys[subsys_id];
	child_css = child->subsys[subsys_id];
	parent_id = rcu_dereference_protected(parent_css->id, true);
	depth = parent_id->depth + 1;

	child_id = get_new_cssid(ss, depth);
	if (IS_ERR(child_id))
		return PTR_ERR(child_id);

	for (i = 0; i < depth; i++)
		child_id->stack[i] = parent_id->stack[i];
	child_id->stack[depth] = child_id->id;
	/*
	 * child_id->css pointer will be set after this cgroup is available
	 * see cgroup_populate_dir()
	 */
	rcu_assign_pointer(child_css->id, child_id);

	return 0;
}

/**
 * css_lookup - lookup css by id
 * @ss: cgroup subsys to be looked into.
 * @id: the id
 *
 * Returns pointer to cgroup_subsys_state if there is valid one with id.
 * NULL if not. Should be called under rcu_read_lock()
 */
struct cgroup_subsys_state *css_lookup(struct cgroup_subsys *ss, int id)
{
	struct css_id *cssid = NULL;

	BUG_ON(!ss->use_id);
	cssid = idr_find(&ss->idr, id);

	if (unlikely(!cssid))
		return NULL;

	return rcu_dereference(cssid->css);
}
EXPORT_SYMBOL_GPL(css_lookup);

/*
 * get corresponding css from file open on cgroupfs directory
 */
struct cgroup_subsys_state *cgroup_css_from_dir(struct file *f, int id)
{
	struct cgroup *cgrp;
	struct inode *inode;
	struct cgroup_subsys_state *css;

	inode = file_inode(f);
	/* check in cgroup filesystem dir */
	if (inode->i_op != &cgroup_dir_inode_operations)
		return ERR_PTR(-EBADF);

	if (id < 0 || id >= CGROUP_SUBSYS_COUNT)
		return ERR_PTR(-EINVAL);

	/* get cgroup */
	cgrp = __d_cgrp(f->f_dentry);
	css = cgrp->subsys[id];
	return css ? css : ERR_PTR(-ENOENT);
}

#ifdef CONFIG_CGROUP_DEBUG
static struct cgroup_subsys_state *debug_css_alloc(struct cgroup *cgrp)
{
	struct cgroup_subsys_state *css = kzalloc(sizeof(*css), GFP_KERNEL);

	if (!css)
		return ERR_PTR(-ENOMEM);

	return css;
}

static void debug_css_free(struct cgroup *cgrp)
{
	kfree(cgrp->subsys[debug_subsys_id]);
}

static u64 debug_taskcount_read(struct cgroup *cgrp, struct cftype *cft)
{
	return cgroup_task_count(cgrp);
}

static u64 current_css_set_read(struct cgroup *cgrp, struct cftype *cft)
{
	return (u64)(unsigned long)current->cgroups;
}