| Commit message (Collapse) | Author | Age |
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There's nothing atomic about atomic_set vs atomic_read; so remove the
atomic_t usage.
Also, make running_sample_length static as it really is (and should
be) local to this translation unit.
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: eranian@google.com
Cc: Don Zickus <dzickus@redhat.com>
Cc: jmario@redhat.com
Cc: acme@infradead.org
Cc: dave.hansen@linux.intel.com
Link: http://lkml.kernel.org/n/tip-vw9lg588x1ic248whybjon0c@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Conflicts:
tools/perf/builtin-record.c
tools/perf/builtin-top.c
tools/perf/util/hist.h
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Merge Linux v3.12-rc5, to pick up the latest fixes.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Add a generic qualifier for transaction events, as a new sample
type that returns a flag word. This is particularly useful
for qualifying aborts: to distinguish aborts which happen
due to asynchronous events (like conflicts caused by another
CPU) versus instructions that lead to an abort.
The tuning strategies are very different for those cases,
so it's important to distinguish them easily and early.
Since it's inconvenient and inflexible to filter for this
in the kernel we report all the events out and allow
some post processing in user space.
The flags are based on the Intel TSX events, but should be fairly
generic and mostly applicable to other HTM architectures too. In addition
to various flag words there's also reserved space to report an
program supplied abort code. For TSX this is used to distinguish specific
classes of aborts, like a lock busy abort when doing lock elision.
Flags:
Elision and generic transactions (ELISION vs TRANSACTION)
(HLE vs RTM on TSX; IBM etc. would likely only use TRANSACTION)
Aborts caused by current thread vs aborts caused by others (SYNC vs ASYNC)
Retryable transaction (RETRY)
Conflicts with other threads (CONFLICT)
Transaction write capacity overflow (CAPACITY WRITE)
Transaction read capacity overflow (CAPACITY READ)
Transactions implicitely aborted can also return an abort code.
This can be used to signal specific events to the profiler. A common
case is abort on lock busy in a RTM eliding library (code 0xff)
To handle this case we include the TSX abort code
Common example aborts in TSX would be:
- Data conflict with another thread on memory read.
Flags: TRANSACTION|ASYNC|CONFLICT
- executing a WRMSR in a transaction. Flags: TRANSACTION|SYNC
- HLE transaction in user space is too large
Flags: ELISION|SYNC|CAPACITY-WRITE
The only flag that is somewhat TSX specific is ELISION.
This adds the perf core glue needed for reporting the new flag word out.
v2: Add MEM/MISC
v3: Move transaction to the end
v4: Separate capacity-read/write and remove misc
v5: Remove _SAMPLE. Move abort flags to 32bit. Rename
transaction to txn
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1379688044-14173-2-git-send-email-andi@firstfloor.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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/proc/sys/kernel/perf_event_max_sample_rate will accept
negative values as well as 0.
Negative values are unreasonable, and 0 causes a
divide by zero exception in perf_proc_update_handler.
This patch enforces a lower limit of 1.
Signed-off-by: Knut Petersen <Knut_Petersen@t-online.de>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/5242DB0C.4070005@t-online.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull leftover IRQ fixes from Ingo Molnar:
"Two (minor) fixlets that missed v3.12"
* 'irq-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
genirq: Set the irq thread policy without checking CAP_SYS_NICE
irq: DocBook/genericirq.tmpl: Correct various typos
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In commit ee23871389 ("genirq: Set irq thread to RT priority on
creation") we moved the assigment of the thread's priority from the
thread's function into __setup_irq(). That function may run in user
context for instance if the user opens an UART node and then driver
calls requests in the ->open() callback. That user may not have
CAP_SYS_NICE and so the irq thread won't run with the SCHED_OTHER
policy.
This patch uses sched_setscheduler_nocheck() so we omit the CAP_SYS_NICE
check which is otherwise required for the SCHED_OTHER policy.
[bigeasy: Rewrite the changelog]
Signed-off-by: Thomas Pfaff <tpfaff@pcs.com>
Cc: Ivo Sieben <meltedpianoman@gmail.com>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/1381489240-29626-1-git-send-email-bigeasy@linutronix.de
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull IRQ changes from Ingo Molnar:
"The biggest change this cycle are the softirq/hardirq stack
interaction and nesting fixes, cleanups and reorganizations from
Frederic. This is the longer followup story to the softirq nesting
fix that is already upstream (commit ded797547548: "irq: Force hardirq
exit's softirq processing on its own stack")"
* 'irq-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
irqchip: bcm2835: Convert to use IRQCHIP_DECLARE macro
powerpc: Tell about irq stack coverage
x86: Tell about irq stack coverage
irq: Optimize softirq stack selection in irq exit
irq: Justify the various softirq stack choices
irq: Improve a bit softirq debugging
irq: Optimize call to softirq on hardirq exit
irq: Consolidate do_softirq() arch overriden implementations
x86/irq: Correct comment about i8259 initialization
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If irq_exit() is called on the arch's specified irq stack,
it should be safe to run softirqs inline under that same
irq stack as it is near empty by the time we call irq_exit().
For example if we use the same stack for both hard and soft irqs here,
the worst case scenario is:
hardirq -> softirq -> hardirq. But then the softirq supersedes the
first hardirq as the stack user since irq_exit() is called in
a mostly empty stack. So the stack merge in this case looks acceptable.
Stack overrun still have a chance to happen if hardirqs have more
opportunities to nest, but then it's another problem to solve.
So lets adapt the irq exit's softirq stack on top of a new Kconfig symbol
that can be defined when irq_exit() runs on the irq stack. That way
we can spare some stack switch on irq processing and all the cache
issues that come along.
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@au1.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Mackerras <paulus@au1.ibm.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: James E.J. Bottomley <jejb@parisc-linux.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
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For clarity, comment the various stack choices for softirqs
processing, whether we execute them from ksoftirqd or
local_irq_enable() calls.
Their use on irq_exit() is already commented.
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@au1.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Mackerras <paulus@au1.ibm.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: James E.J. Bottomley <jejb@parisc-linux.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
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do_softirq() has a debug check that verifies that it is not nesting
on softirqs processing, nor miscounting the softirq part of the preempt
count.
But making sure that softirqs processing don't nest is actually a more
generic concern that applies to any caller of __do_softirq().
Do take it one step further and generalize that debug check to
any softirq processing.
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@au1.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Mackerras <paulus@au1.ibm.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: James E.J. Bottomley <jejb@parisc-linux.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
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Before processing softirqs on hardirq exit, we already
do the check for pending softirqs while hardirqs are
guaranteed to be disabled.
So we can take a shortcut and safely jump to the arch
specific implementation directly.
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@au1.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Mackerras <paulus@au1.ibm.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: James E.J. Bottomley <jejb@parisc-linux.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
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All arch overriden implementations of do_softirq() share the following
common code: disable irqs (to avoid races with the pending check),
check if there are softirqs pending, then execute __do_softirq() on
a specific stack.
Consolidate the common parts such that archs only worry about the
stack switch.
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@au1.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Mackerras <paulus@au1.ibm.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: James E.J. Bottomley <jejb@parisc-linux.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull RCU updates from Ingo Molnar:
"The main RCU changes in this cycle are:
- Idle entry/exit changes, to throttle callback execution and other
refinements to speed up kbuild, primarily to address performance
issues located by Tibor Billes.
- Grace-period related changes, primarily to aid in debugging,
inspired by an -rt debugging session.
- Code reorganization moving RCU's source files into its own
kernel/rcu/ directory.
- RCU documentation updates
- Miscellaneous fixes.
Note, the following commit:
5c889690aa08 mm: Place preemption point in do_mlockall() loop
is identical to the commit already in your tree via email:
22356f447ceb mm: Place preemption point in do_mlockall() loop
[ Your version of the changelog nicely demonstrates it how kernel oops
messages should be trimmed properly :-/ ]"
* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (30 commits)
rcu: Move RCU-related source code to kernel/rcu directory
rcu: Fix occurrence of "the the" in checklist.txt
kthread: Add pointer to vmstat-avoidance patch
rcu: Update stall-warning documentation
rcu: Consistent rcu_is_watching() naming
rcu: Change EXPORT_SYMBOL() to EXPORT_SYMBOL_GPL()
rcu: Is it safe to enter an RCU read-side critical section?
rcu: Throttle invoke_rcu_core() invocations due to non-lazy callbacks
rcu: Throttle rcu_try_advance_all_cbs() execution
rcu: Remove redundant code from rcu_cleanup_after_idle()
rcu: Fix CONFIG_RCU_NOCB_CPU_ALL panic on machines with sparse CPU mask
rcu: Avoid sparse warnings in rcu_nocb_wake trace event
rcu: Track rcu_nocb_kthread()'s sleeping and awakening
rcu: Distinguish between NOCB and non-NOCB rcu_callback trace events
rcu: Add tracing for rcuo no-CBs CPU wakeup handshake
rcu: Add tracing of normal (non-NOCB) grace-period requests
rcu: Add tracing to rcu_gp_kthread()
rcu: Flag lockless access to ->gp_flags with ACCESS_ONCE()
rcu: Prevent spurious-wakeup DoS attack on rcu_gp_kthread()
rcu: Improve grace-period start logic
...
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git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/rcu
Pull RCU updates from Paul E. McKenney.
Major changes:
" 1. Update RCU documentation. These were posted to LKML at
http://article.gmane.org/gmane.linux.kernel/1566994.
2. Miscellaneous fixes. These were posted to LKML at
http://article.gmane.org/gmane.linux.kernel/1567027.
3. Grace-period-related changes, primarily to aid in debugging,
inspired by a -rt debugging session. These were posted to
LKML at http://article.gmane.org/gmane.linux.kernel/1567076.
4. Idle entry/exit changes, primarily to address issues located
by Tibor Billes. These were posted to LKML at
http://article.gmane.org/gmane.linux.kernel/1567096.
5. Code reorganization moving RCU's source files from kernel
to kernel/rcu. This was posted to LKML at
http://article.gmane.org/gmane.linux.kernel/1577344."
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
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idle.2013.09.25a: Topic branch for idle entry-/exit-related changes.
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The old rcu_is_cpu_idle() function is just __rcu_is_watching() with
preemption disabled. This commit therefore renames rcu_is_cpu_idle()
to rcu_is_watching.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
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Commit e6b80a3b (rcu: Detect illegal rcu dereference in extended
quiescent state) exported the pre-existing rcu_is_cpu_idle() function
using EXPORT_SYMBOL(). However, this is inconsistent with the remaining
exports from RCU, which are all EXPORT_SYMBOL_GPL(). The current state
of affairs means that a non-GPL module could use rcu_is_cpu_idle(),
but in a CONFIG_TREE_PREEMPT_RCU=y kernel would be unable to invoke
rcu_read_lock() and rcu_read_unlock().
This commit therefore makes rcu_is_cpu_idle()'s export be consistent
with the rest of RCU, namely EXPORT_SYMBOL_GPL().
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
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There is currently no way for kernel code to determine whether it
is safe to enter an RCU read-side critical section, in other words,
whether or not RCU is paying attention to the currently running CPU.
Given the large and increasing quantity of code shared by the idle loop
and non-idle code, the this shortcoming is becoming increasingly painful.
This commit therefore adds __rcu_is_watching(), which returns true if
it is safe to enter an RCU read-side critical section on the currently
running CPU. This function is quite fast, using only a __this_cpu_read().
However, the caller must disable preemption.
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
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If a non-lazy callback arrives on a CPU that has previously gone idle
with no non-lazy callbacks, invoke_rcu_core() forces the RCU core to
run. However, it does not update the conditions, which could result
in several closely spaced invocations of the RCU core, which in turn
could result in an excessively high context-switch rate and resulting
high overhead.
This commit therefore updates the ->all_lazy and ->nonlazy_posted_snap
fields to prevent closely spaced invocations.
Reported-by: Tibor Billes <tbilles@gmx.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Tibor Billes <tbilles@gmx.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
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The rcu_try_advance_all_cbs() function is invoked on each attempted
entry to and every exit from idle. If this function determines that
there are callbacks ready to invoke, the caller will invoke the RCU
core, which in turn will result in a pair of context switches. If a
CPU enters and exits idle extremely frequently, this can result in
an excessive number of context switches and high CPU overhead.
This commit therefore causes rcu_try_advance_all_cbs() to throttle
itself, refusing to do work more than once per jiffy.
Reported-by: Tibor Billes <tbilles@gmx.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Tibor Billes <tbilles@gmx.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
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The rcu_try_advance_all_cbs() function returns a bool saying whether or
not there are callbacks ready to invoke, but rcu_cleanup_after_idle()
rechecks this regardless. This commit therefore uses the value returned
by rcu_try_advance_all_cbs() instead of making rcu_cleanup_after_idle()
do this recheck.
Reported-by: Tibor Billes <tbilles@gmx.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Tibor Billes <tbilles@gmx.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
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gp.2013.09.25a: Topic branch for grace-period updates.
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The event-tracing macros do not like bool tracing arguments, so this
commit makes them be of type char. This change has the knock-on effect
of making it illegal to pass a pointer into one of these arguments, so
also change rcutiny's first call to trace_rcu_batch_end() to convert
from pointer to boolean, prefixing with "!!".
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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This commit adds event traces to track all of rcu_nocb_kthread()'s
blocking and awakening.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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One way to distinguish between NOCB and non-NOCB rcu_callback trace
events is that the former always print zero for the lazy and non-lazy
queue lengths. Unfortunately, this also means that we cannot see the NOCB
queue lengths. This commit therefore accesses the NOCB queue lengths,
but negates them. NOCB rcu_callback trace events should therefore have
negative queue lengths.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Match operand size per kbuild test robot's advice. ]
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Lost wakeups from call_rcu() to the rcuo kthreads can result in hangs
that are difficult to diagnose. This commit therefore adds tracing to
help pin down the cause of these hangs.
Reported-by: Clark Williams <williams@redhat.com>
Reported-by: Carsten Emde <C.Emde@osadl.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Add const per kbuild test robot's advice. ]
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This commit adds tracing to the normal grace-period request points.
These are rcu_gp_cleanup(), which checks for the need for another
grace period at the end of the previous grace period, and
rcu_start_gp_advanced(), which restarts RCU's state machine after
an idle period. These trace events are intended to help track down
bugs where RCU remains idle despite there being work for it to do.
Reported-by: Clark Williams <williams@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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This commit adds tracing to the rcu_gp_kthread() function in order to
help trace down hangs potentially involving this kthread.
Reported-by: Clark Williams <williams@redhat.com>
Reported-by: Carsten Emde <C.Emde@osadl.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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This commit applies ACCESS_ONCE() to an outside-of-lock access to
->gp_flags. Although it is hard to imagine any sane compiler messing
this particular case up, the documentation benefits are substantial.
Plus the definition of "sane compiler" grows ever looser.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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Spurious wakeups in the force-quiescent-state loop in rcu_gp_kthread()
cause the timeout to be recalculated, which would prevent rcu_gp_fqs()
from ever being called. This would in turn would prevent the grace period
from ever ending for as long as there was at least one CPU in an extended
quiescent state that had not yet passed through a quiescent state.
This commit therefore avoids recalculating the timeout unless the
previous pass's call to wait_event_interruptible_timeout() actually
did time out, thus preventing the above scenario.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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This commit improves grace-period start logic by checking ->gp_flags
under the lock and by issuing a warning if a grace period is already
in progress.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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Some architectures have sparse cpu mask. UltraSparc's cpuinfo for example:
CPU0: online
CPU2: online
So, set only possible CPUs when CONFIG_RCU_NOCB_CPU_ALL is enabled.
Also, check that user passes right 'rcu_nocbs=' option.
Signed-off-by: Kirill Tkhai <tkhai@yandex.ru>
CC: Dipankar Sarma <dipankar@in.ibm.com>
[ paulmck: Fix pr_info() issue noted by scripts/checkpatch.pl. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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This commit extends the work done in f7f7bac9 (rcu: Have the RCU
tracepoints use the tracepoint_string infrastructure) to cover rcutiny.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
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If a system is idle from an RCU perspective for longer than specified
by CONFIG_RCU_CPU_STALL_TIMEOUT, and if one CPU starts a grace period
just as a second checks for CPU stalls, and if this second CPU happens
to see the old value of rsp->jiffies_stall, it will incorrectly report a
CPU stall. This is quite rare, but apparently occurs deterministically
on systems with about 6TB of memory.
This commit therefore orders accesses to the data used to determine
whether or not a CPU stall is in progress. Grace-period initialization
and cleanup first increments rsp->completed to mark the end of the
previous grace period, then records the current jiffies in rsp->gp_start,
then records the jiffies at which a stall can be expected to occur in
rsp->jiffies_stall, and finally increments rsp->gpnum to mark the start
of the new grace period. Now, this ordering by itself does not prevent
false positives. For example, if grace-period initialization was delayed
between recording rsp->gp_start and rsp->jiffies_stall, the CPU stall
warning code might still see an old value of rsp->jiffies_stall.
Therefore, this commit also orders the CPU stall warning accesses as
well, loading rsp->gpnum and jiffies, then rsp->jiffies_stall, then
rsp->gp_start, and finally rsp->completed. This ordering means that
the false-positive scenario in the previous paragraph would result
in rsp->completed being greater than or equal to rsp->gpnum, which is
never valid for a CPU stall, allowing the false positive to be rejected.
Furthermore, any fetch that gets an old value of rsp->jiffies_stall
must also get an old value of rsp->gpnum, which will again be rejected
by the comparison of rsp->gpnum and rsp->completed. Situations where
rsp->gp_start is later than rsp->jiffies_stall are also rejected, as
are situations where jiffies is less than rsp->jiffies_stall.
Although use of unsynchronized accesses means that there are likely
still some false-positive scenarios (synchronization has proven to be
a very bad idea on large systems), this should get rid of a large class
of these scenarios.
Reported-by: Fabian Herschel <fabian.herschel@suse.com>
Reported-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Tested-by: Jochen Striepe <jochen@tolot.escape.de>
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The for_each_rcu_flavor() loop unconditionally scans all flavors, even
when the first flavor might have some non-lazy callbacks. Once the
loop has seen a non-lazy callback, further passes through the loop
cannot change the state. This is not a huge problem, given that there
can be at most three RCU flavors (RCU-bh, RCU-preempt, and RCU-sched),
but this code is on the path to idle, so speeding it up even a small
amount would have some benefit.
This commit therefore does two things:
1. Rearranges the order of the list of RCU flavors in order to
place the most active flavor first in the list. The most active
RCU flavor is RCU-preempt, or, if there is no RCU-preempt,
RCU-sched.
2. Reworks the for_each_rcu_flavor() to exit early when the first
non-lazy callback is seen, or, in the case where the caller
does not care about non-lazy callbacks (RCU_FAST_NO_HZ=n),
when the first callback is seen.
Reported-by: Chen Gang <gang.chen@asianux.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The "idle" variable in both rcu_eqs_enter_common() and
rcu_eqs_exit_common() is only used in a WARN_ON_ONCE(). If the kernel
is built disabling WARN_ON_ONCE(), the compiler will complain (rightly)
that "idle" is unused. This commit therefore adds a __maybe_unused to
the declaration of both variables.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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__get_cpu_var() is used for multiple purposes in the kernel source. One
of them is address calculation via the form &__get_cpu_var(x). This
calculates the address for the instance of the percpu variable of the
current processor based on an offset.
Other use cases are for storing and retrieving data from the current
processors percpu area. __get_cpu_var() can be used as an lvalue when
writing data or on the right side of an assignment.
__get_cpu_var() is defined as :
__get_cpu_var() always only does an address determination. However,
store and retrieve operations could use a segment prefix (or global
register on other platforms) to avoid the address calculation.
this_cpu_write() and this_cpu_read() can directly take an offset into
a percpu area and use optimized assembly code to read and write per
cpu variables.
This patch converts __get_cpu_var into either an explicit address
calculation using this_cpu_ptr() or into a use of this_cpu operations
that use the offset. Thereby address calcualtions are avoided and less
registers are used when code is generated.
At the end of the patchset all uses of __get_cpu_var have been removed
so the macro is removed too.
The patchset includes passes over all arches as well. Once these
operations are used throughout then specialized macros can be defined in
non -x86 arches as well in order to optimize per cpu access by f.e. using
a global register that may be set to the per cpu base.
Transformations done to __get_cpu_var()
1. Determine the address of the percpu instance of the current processor.
DEFINE_PER_CPU(int, y);
int *x = &__get_cpu_var(y);
Converts to
int *x = this_cpu_ptr(&y);
2. Same as #1 but this time an array structure is involved.
DEFINE_PER_CPU(int, y[20]);
int *x = __get_cpu_var(y);
Converts to
int *x = this_cpu_ptr(y);
3. Retrieve the content of the current processors instance of a per cpu
variable.
DEFINE_PER_CPU(int, u);
int x = __get_cpu_var(y)
Converts to
int x = __this_cpu_read(y);
4. Retrieve the content of a percpu struct
DEFINE_PER_CPU(struct mystruct, y);
struct mystruct x = __get_cpu_var(y);
Converts to
memcpy(this_cpu_ptr(&x), y, sizeof(x));
5. Assignment to a per cpu variable
DEFINE_PER_CPU(int, y)
__get_cpu_var(y) = x;
Converts to
this_cpu_write(y, x);
6. Increment/Decrement etc of a per cpu variable
DEFINE_PER_CPU(int, y);
__get_cpu_var(y)++
Converts to
this_cpu_inc(y)
Signed-off-by: Christoph Lameter <cl@linux.com>
[ paulmck: Address conflicts. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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This commit replaces an incorrect (but fortunately functional)
bitwise OR ("|") operator with the correct logical OR ("||").
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The rcu_cpu_stall_timeout kernel parameter, the rcu_dynticks per-CPU
variable, and the rcu_gp_fqs() function are used only locally. This
commit therefore marks them as static.
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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One of the ->gp_flags assignments used a raw number rather than the
cpp macro that was intended for this purpose, which this commit fixes.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace
Pull perf/ftrace fix from Steven Rostedt:
"Dave Jones's trinity program was able to enable the function tracer
from a normal user account via the perf syscall "perf_event_open()".
When I was able to reproduce it with trinity, I was able to track down
exactly how it happened.
I discovered that the check for whether the function tracepoint should
be activated or not was using the "perf_paranoid_kernel()" check which
by default, lets the user continue. The user should not by default be
able to enable function tracing.
The fix is to use "perf_paranoid_tracepoint_raw()" which will not let
the user enable function tracing. This is a security fix as normal
users should never be allowed to enable the function tracer"
* tag 'ftrace-urgent-3.12-v2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
perf/ftrace: Fix paranoid level for enabling function tracer
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The current default perf paranoid level is "1" which has
"perf_paranoid_kernel()" return false, and giving any operations that
use it, access to normal users. Unfortunately, this includes function
tracing and normal users should not be allowed to enable function
tracing by default.
The proper level is defined at "-1" (full perf access), which
"perf_paranoid_tracepoint_raw()" will only give access to. Use that
check instead for enabling function tracing.
Reported-by: Dave Jones <davej@redhat.com>
Reported-by: Vince Weaver <vincent.weaver@maine.edu>
Tested-by: Vince Weaver <vincent.weaver@maine.edu>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: stable@vger.kernel.org # 3.4+
CVE: CVE-2013-2930
Fixes: ced39002f5ea ("ftrace, perf: Add support to use function tracepoint in perf")
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty
Pull tty/serial driver updates from Greg KH:
"Here's the big tty/serial driver update for 3.13-rc1.
There's some more minor n_tty work here, but nothing like previous
kernel releases. Also some new driver ids, driver updates for new
hardware, and other small things.
All of this has been in linux-next for a while with no issues"
* tag 'tty-3.13-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty: (84 commits)
serial: omap: fix missing comma
serial: sh-sci: Enable the driver on all ARM platforms
serial: mfd: Staticize local symbols
serial: omap: fix a few checkpatch warnings
serial: omap: improve RS-485 performance
mrst_max3110: fix unbalanced IRQ issue during resume
serial: omap: Add support for optional wake-up
serial: sirf: remove duplicate defines
tty: xuartps: Fix build error when COMMON_CLK is not set
tty: xuartps: Fix build error due to missing forward declaration
tty: xuartps: Fix "may be used uninitialized" build warning
serial: 8250_pci: add Pericom PCIe Serial board Support (12d8:7952/4/8) - Chip PI7C9X7952/4/8
tty: xuartps: Update copyright information
tty: xuartps: Implement suspend/resume callbacks
tty: xuartps: Dynamically adjust to input frequency changes
tty: xuartps: Updating set_baud_rate()
tty: xuartps: Force enable the UART in xuartps_console_write
tty: xuartps: support 64 byte FIFO size
tty: xuartps: Add polled mode support for xuartps
tty: xuartps: Implement BREAK detection, add SYSRQ support
...
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Turn the initial value of sysctl kernel.sysrq (SYSRQ_DEFAULT_ENABLE)
into a Kconfig variable.
Original version by Bastian Blank <waldi@debian.org>.
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core
Pull driver core / sysfs patches from Greg KH:
"Here's the big driver core / sysfs update for 3.13-rc1.
There's lots of dev_groups updates for different subsystems, as they
all get slowly migrated over to the safe versions of the attribute
groups (removing userspace races with the creation of the sysfs
files.) Also in here are some kobject updates, devres expansions, and
the first round of Tejun's sysfs reworking to enable it to be used by
other subsystems as a backend for an in-kernel filesystem.
All of these have been in linux-next for a while with no reported
issues"
* tag 'driver-core-3.13-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core: (83 commits)
sysfs: rename sysfs_assoc_lock and explain what it's about
sysfs: use generic_file_llseek() for sysfs_file_operations
sysfs: return correct error code on unimplemented mmap()
mdio_bus: convert bus code to use dev_groups
device: Make dev_WARN/dev_WARN_ONCE print device as well as driver name
sysfs: separate out dup filename warning into a separate function
sysfs: move sysfs_hash_and_remove() to fs/sysfs/dir.c
sysfs: remove unused sysfs_get_dentry() prototype
sysfs: honor bin_attr.attr.ignore_lockdep
sysfs: merge sysfs_elem_bin_attr into sysfs_elem_attr
devres: restore zeroing behavior of devres_alloc()
sysfs: fix sysfs_write_file for bin file
input: gameport: convert bus code to use dev_groups
input: serio: remove bus usage of dev_attrs
input: serio: use DEVICE_ATTR_RO()
i2o: convert bus code to use dev_groups
memstick: convert bus code to use dev_groups
tifm: convert bus code to use dev_groups
virtio: convert bus code to use dev_groups
ipack: convert bus code to use dev_groups
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We want these fixes here too.
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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We want the driver core and sysfs fixes in here to make merges and
development easier.
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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The dev_attrs field of struct bus_type is going away soon, dev_groups
should be used instead. This converts the pmu bus code to use
the correct field.
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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