Merge branch 'mpi-master' into wip-k-fmlpwip-k-fmlp

Conflicts:
	litmus/sched_cedf.c

5 files changed, 472 insertions, 88 deletions

diff --git a/Documentation/RCU/00-INDEX b/Documentation/RCU/00-INDEX
index 71b6f500ddb9..1d7a885761f5 100644
--- a/Documentation/RCU/00-INDEX
+++ b/Documentation/RCU/00-INDEX
@@ -21,7 +21,7 @@ rcu.txt
 RTFP.txt
         - List of RCU papers (bibliography) going back to 1980.
 stallwarn.txt
-        - RCU CPU stall warnings (CONFIG_RCU_CPU_STALL_DETECTOR)
+        - RCU CPU stall warnings (module parameter rcu_cpu_stall_suppress)
 torture.txt
         - RCU Torture Test Operation (CONFIG_RCU_TORTURE_TEST)
 trace.txt
diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt
index 790d1a812376..0c134f8afc6f 100644
--- a/Documentation/RCU/checklist.txt
+++ b/Documentation/RCU/checklist.txt
@@ -218,13 +218,22 @@ over a rather long period of time, but improvements are always welcome!
         include:
 
         a.      Keeping a count of the number of data-structure elements
-                used by the RCU-protected data structure, including those
-                waiting for a grace period to elapse.  Enforce a limit
-                on this number, stalling updates as needed to allow
-                previously deferred frees to complete.
-
-                Alternatively, limit only the number awaiting deferred
-                free rather than the total number of elements.
+                used by the RCU-protected data structure, including
+                those waiting for a grace period to elapse.  Enforce a
+                limit on this number, stalling updates as needed to allow
+                previously deferred frees to complete.  Alternatively,
+                limit only the number awaiting deferred free rather than
+                the total number of elements.
+
+                One way to stall the updates is to acquire the update-side
+                mutex.  (Don't try this with a spinlock -- other CPUs
+                spinning on the lock could prevent the grace period
+                from ever ending.)  Another way to stall the updates
+                is for the updates to use a wrapper function around
+                the memory allocator, so that this wrapper function
+                simulates OOM when there is too much memory awaiting an
+                RCU grace period.  There are of course many other
+                variations on this theme.
 
         b.      Limiting update rate.  For example, if updates occur only
                 once per hour, then no explicit rate limiting is required,
@@ -365,3 +374,26 @@ over a rather long period of time, but improvements are always welcome!
         and the compiler to freely reorder code into and out of RCU
         read-side critical sections.  It is the responsibility of the
         RCU update-side primitives to deal with this.
+
+17.     Use CONFIG_PROVE_RCU, CONFIG_DEBUG_OBJECTS_RCU_HEAD, and
+        the __rcu sparse checks to validate your RCU code.  These
+        can help find problems as follows:
+
+        CONFIG_PROVE_RCU: check that accesses to RCU-protected data
+                structures are carried out under the proper RCU
+                read-side critical section, while holding the right
+                combination of locks, or whatever other conditions
+                are appropriate.
+
+        CONFIG_DEBUG_OBJECTS_RCU_HEAD: check that you don't pass the
+                same object to call_rcu() (or friends) before an RCU
+                grace period has elapsed since the last time that you
+                passed that same object to call_rcu() (or friends).
+
+        __rcu sparse checks: tag the pointer to the RCU-protected data
+                structure with __rcu, and sparse will warn you if you
+                access that pointer without the services of one of the
+                variants of rcu_dereference().
+
+        These debugging aids can help you find problems that are
+        otherwise extremely difficult to spot.
diff --git a/Documentation/RCU/stallwarn.txt b/Documentation/RCU/stallwarn.txt
index 44c6dcc93d6d..4e959208f736 100644
--- a/Documentation/RCU/stallwarn.txt
+++ b/Documentation/RCU/stallwarn.txt
@@ -1,22 +1,25 @@
 Using RCU's CPU Stall Detector
 
-The CONFIG_RCU_CPU_STALL_DETECTOR kernel config parameter enables
-RCU's CPU stall detector, which detects conditions that unduly delay
-RCU grace periods.  The stall detector's idea of what constitutes
-"unduly delayed" is controlled by a set of C preprocessor macros:
+The rcu_cpu_stall_suppress module parameter enables RCU's CPU stall
+detector, which detects conditions that unduly delay RCU grace periods.
+This module parameter enables CPU stall detection by default, but
+may be overridden via boot-time parameter or at runtime via sysfs.
+The stall detector's idea of what constitutes "unduly delayed" is
+controlled by a set of kernel configuration variables and cpp macros:
 
-RCU_SECONDS_TILL_STALL_CHECK
+CONFIG_RCU_CPU_STALL_TIMEOUT
 
-        This macro defines the period of time that RCU will wait from
-        the beginning of a grace period until it issues an RCU CPU
-        stall warning.  This time period is normally ten seconds.
+        This kernel configuration parameter defines the period of time
+        that RCU will wait from the beginning of a grace period until it
+        issues an RCU CPU stall warning.  This time period is normally
+        ten seconds.
 
 RCU_SECONDS_TILL_STALL_RECHECK
 
         This macro defines the period of time that RCU will wait after
         issuing a stall warning until it issues another stall warning
-        for the same stall.  This time period is normally set to thirty
-        seconds.
+        for the same stall.  This time period is normally set to three
+        times the check interval plus thirty seconds.
 
 RCU_STALL_RAT_DELAY
 
@@ -80,6 +83,24 @@ o	A CPU looping with bottom halves disabled.  This condition can
 o       For !CONFIG_PREEMPT kernels, a CPU looping anywhere in the kernel
         without invoking schedule().
 
+o       A CPU-bound real-time task in a CONFIG_PREEMPT kernel, which might
+        happen to preempt a low-priority task in the middle of an RCU
+        read-side critical section.   This is especially damaging if
+        that low-priority task is not permitted to run on any other CPU,
+        in which case the next RCU grace period can never complete, which
+        will eventually cause the system to run out of memory and hang.
+        While the system is in the process of running itself out of
+        memory, you might see stall-warning messages.
+
+o       A CPU-bound real-time task in a CONFIG_PREEMPT_RT kernel that
+        is running at a higher priority than the RCU softirq threads.
+        This will prevent RCU callbacks from ever being invoked,
+        and in a CONFIG_TREE_PREEMPT_RCU kernel will further prevent
+        RCU grace periods from ever completing.  Either way, the
+        system will eventually run out of memory and hang.  In the
+        CONFIG_TREE_PREEMPT_RCU case, you might see stall-warning
+        messages.
+
 o       A bug in the RCU implementation.
 
 o       A hardware failure.  This is quite unlikely, but has occurred
diff --git a/Documentation/RCU/trace.txt b/Documentation/RCU/trace.txt
index efd8cc95c06b..8173cec473aa 100644
--- a/Documentation/RCU/trace.txt
+++ b/Documentation/RCU/trace.txt
@@ -1,39 +1,55 @@
 CONFIG_RCU_TRACE debugfs Files and Formats
 
 
-The rcutree implementation of RCU provides debugfs trace output that
-summarizes counters and state.  This information is useful for debugging
-RCU itself, and can sometimes also help to debug abuses of RCU.
-The following sections describe the debugfs files and formats.
-
-
-Hierarchical RCU debugfs Files and Formats
-
-This implementation of RCU provides three debugfs files under the
-top-level directory RCU: rcu/rcudata (which displays fields in struct
-rcu_data), rcu/rcugp (which displays grace-period counters), and
-rcu/rcuhier (which displays the struct rcu_node hierarchy).
+The rcutree and rcutiny implementations of RCU provide debugfs trace
+output that summarizes counters and state.  This information is useful for
+debugging RCU itself, and can sometimes also help to debug abuses of RCU.
+The following sections describe the debugfs files and formats, first
+for rcutree and next for rcutiny.
+
+
+CONFIG_TREE_RCU and CONFIG_TREE_PREEMPT_RCU debugfs Files and Formats
+
+These implementations of RCU provides several debugfs files under the
+top-level directory "rcu":
+
+rcu/rcudata:
+        Displays fields in struct rcu_data.
+rcu/rcudata.csv:
+        Comma-separated values spreadsheet version of rcudata.
+rcu/rcugp:
+        Displays grace-period counters.
+rcu/rcuhier:
+        Displays the struct rcu_node hierarchy.
+rcu/rcu_pending:
+        Displays counts of the reasons rcu_pending() decided that RCU had
+        work to do.
+rcu/rcutorture:
+        Displays rcutorture test progress.
+rcu/rcuboost:
+        Displays RCU boosting statistics.  Only present if
+        CONFIG_RCU_BOOST=y.
 
 The output of "cat rcu/rcudata" looks as follows:
 
 rcu_sched:
-  0 c=17829 g=17829 pq=1 pqc=17829 qp=0 dt=10951/1 dn=0 df=1101 of=0 ri=36 ql=0 b=10
-  1 c=17829 g=17829 pq=1 pqc=17829 qp=0 dt=16117/1 dn=0 df=1015 of=0 ri=0 ql=0 b=10
-  2 c=17829 g=17829 pq=1 pqc=17829 qp=0 dt=1445/1 dn=0 df=1839 of=0 ri=0 ql=0 b=10
-  3 c=17829 g=17829 pq=1 pqc=17829 qp=0 dt=6681/1 dn=0 df=1545 of=0 ri=0 ql=0 b=10
-  4 c=17829 g=17829 pq=1 pqc=17829 qp=0 dt=1003/1 dn=0 df=1992 of=0 ri=0 ql=0 b=10
-  5 c=17829 g=17830 pq=1 pqc=17829 qp=1 dt=3887/1 dn=0 df=3331 of=0 ri=4 ql=2 b=10
-  6 c=17829 g=17829 pq=1 pqc=17829 qp=0 dt=859/1 dn=0 df=3224 of=0 ri=0 ql=0 b=10
-  7 c=17829 g=17830 pq=0 pqc=17829 qp=1 dt=3761/1 dn=0 df=1818 of=0 ri=0 ql=2 b=10
+  0 c=20972 g=20973 pq=1 pqc=20972 qp=0 dt=545/1/0 df=50 of=0 ri=0 ql=163 qs=NRW. kt=0/W/0 ktl=ebc3 b=10 ci=153737 co=0 ca=0
+  1 c=20972 g=20973 pq=1 pqc=20972 qp=0 dt=967/1/0 df=58 of=0 ri=0 ql=634 qs=NRW. kt=0/W/1 ktl=58c b=10 ci=191037 co=0 ca=0
+  2 c=20972 g=20973 pq=1 pqc=20972 qp=0 dt=1081/1/0 df=175 of=0 ri=0 ql=74 qs=N.W. kt=0/W/2 ktl=da94 b=10 ci=75991 co=0 ca=0
+  3 c=20942 g=20943 pq=1 pqc=20942 qp=1 dt=1846/0/0 df=404 of=0 ri=0 ql=0 qs=.... kt=0/W/3 ktl=d1cd b=10 ci=72261 co=0 ca=0
+  4 c=20972 g=20973 pq=1 pqc=20972 qp=0 dt=369/1/0 df=83 of=0 ri=0 ql=48 qs=N.W. kt=0/W/4 ktl=e0e7 b=10 ci=128365 co=0 ca=0
+  5 c=20972 g=20973 pq=1 pqc=20972 qp=0 dt=381/1/0 df=64 of=0 ri=0 ql=169 qs=NRW. kt=0/W/5 ktl=fb2f b=10 ci=164360 co=0 ca=0
+  6 c=20972 g=20973 pq=1 pqc=20972 qp=0 dt=1037/1/0 df=183 of=0 ri=0 ql=62 qs=N.W. kt=0/W/6 ktl=d2ad b=10 ci=65663 co=0 ca=0
+  7 c=20897 g=20897 pq=1 pqc=20896 qp=0 dt=1572/0/0 df=382 of=0 ri=0 ql=0 qs=.... kt=0/W/7 ktl=cf15 b=10 ci=75006 co=0 ca=0
 rcu_bh:
-  0 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=10951/1 dn=0 df=0 of=0 ri=0 ql=0 b=10
-  1 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=16117/1 dn=0 df=13 of=0 ri=0 ql=0 b=10
-  2 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=1445/1 dn=0 df=15 of=0 ri=0 ql=0 b=10
-  3 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=6681/1 dn=0 df=9 of=0 ri=0 ql=0 b=10
-  4 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=1003/1 dn=0 df=15 of=0 ri=0 ql=0 b=10
-  5 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=3887/1 dn=0 df=15 of=0 ri=0 ql=0 b=10
-  6 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=859/1 dn=0 df=15 of=0 ri=0 ql=0 b=10
-  7 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=3761/1 dn=0 df=15 of=0 ri=0 ql=0 b=10
+  0 c=1480 g=1480 pq=1 pqc=1479 qp=0 dt=545/1/0 df=6 of=0 ri=1 ql=0 qs=.... kt=0/W/0 ktl=ebc3 b=10 ci=0 co=0 ca=0
+  1 c=1480 g=1480 pq=1 pqc=1479 qp=0 dt=967/1/0 df=3 of=0 ri=1 ql=0 qs=.... kt=0/W/1 ktl=58c b=10 ci=151 co=0 ca=0
+  2 c=1480 g=1480 pq=1 pqc=1479 qp=0 dt=1081/1/0 df=6 of=0 ri=1 ql=0 qs=.... kt=0/W/2 ktl=da94 b=10 ci=0 co=0 ca=0
+  3 c=1480 g=1480 pq=1 pqc=1479 qp=0 dt=1846/0/0 df=8 of=0 ri=1 ql=0 qs=.... kt=0/W/3 ktl=d1cd b=10 ci=0 co=0 ca=0
+  4 c=1480 g=1480 pq=1 pqc=1479 qp=0 dt=369/1/0 df=6 of=0 ri=1 ql=0 qs=.... kt=0/W/4 ktl=e0e7 b=10 ci=0 co=0 ca=0
+  5 c=1480 g=1480 pq=1 pqc=1479 qp=0 dt=381/1/0 df=4 of=0 ri=1 ql=0 qs=.... kt=0/W/5 ktl=fb2f b=10 ci=0 co=0 ca=0
+  6 c=1480 g=1480 pq=1 pqc=1479 qp=0 dt=1037/1/0 df=6 of=0 ri=1 ql=0 qs=.... kt=0/W/6 ktl=d2ad b=10 ci=0 co=0 ca=0
+  7 c=1474 g=1474 pq=1 pqc=1473 qp=0 dt=1572/0/0 df=8 of=0 ri=1 ql=0 qs=.... kt=0/W/7 ktl=cf15 b=10 ci=0 co=0 ca=0
 
 The first section lists the rcu_data structures for rcu_sched, the second
 for rcu_bh.  Note that CONFIG_TREE_PREEMPT_RCU kernels will have an
@@ -48,17 +64,18 @@ o	The number at the beginning of each line is the CPU number.
         substantially larger than the number of actual CPUs.
 
 o       "c" is the count of grace periods that this CPU believes have
-        completed.  CPUs in dynticks idle mode may lag quite a ways
-        behind, for example, CPU 4 under "rcu_sched" above, which has
-        slept through the past 25 RCU grace periods.  It is not unusual
-        to see CPUs lagging by thousands of grace periods.
+        completed.  Offlined CPUs and CPUs in dynticks idle mode may
+        lag quite a ways behind, for example, CPU 6 under "rcu_sched"
+        above, which has been offline through not quite 40,000 RCU grace
+        periods.  It is not unusual to see CPUs lagging by thousands of
+        grace periods.
 
 o       "g" is the count of grace periods that this CPU believes have
-        started.  Again, CPUs in dynticks idle mode may lag behind.
-        If the "c" and "g" values are equal, this CPU has already
-        reported a quiescent state for the last RCU grace period that
-        it is aware of, otherwise, the CPU believes that it owes RCU a
-        quiescent state.
+        started.  Again, offlined CPUs and CPUs in dynticks idle mode
+        may lag behind.  If the "c" and "g" values are equal, this CPU
+        has already reported a quiescent state for the last RCU grace
+        period that it is aware of, otherwise, the CPU believes that it
+        owes RCU a quiescent state.
 
 o       "pq" indicates that this CPU has passed through a quiescent state
         for the current grace period.  It is possible for "pq" to be
@@ -77,22 +94,16 @@ o	"pqc" indicates which grace period the last-observed quiescent
         the next grace period!
 
 o       "qp" indicates that RCU still expects a quiescent state from
-        this CPU.
+        this CPU.  Offlined CPUs and CPUs in dyntick idle mode might
+        well have qp=1, which is OK: RCU is still ignoring them.
 
 o       "dt" is the current value of the dyntick counter that is incremented
         when entering or leaving dynticks idle state, either by the
-        scheduler or by irq.  The number after the "/" is the interrupt
-        nesting depth when in dyntick-idle state, or one greater than
-        the interrupt-nesting depth otherwise.
-
-        This field is displayed only for CONFIG_NO_HZ kernels.
-
-o       "dn" is the current value of the dyntick counter that is incremented
-        when entering or leaving dynticks idle state via NMI.  If both
-        the "dt" and "dn" values are even, then this CPU is in dynticks
-        idle mode and may be ignored by RCU.  If either of these two
-        counters is odd, then RCU must be alert to the possibility of
-        an RCU read-side critical section running on this CPU.
+        scheduler or by irq.  This number is even if the CPU is in
+        dyntick idle mode and odd otherwise.  The number after the first
+        "/" is the interrupt nesting depth when in dyntick-idle state,
+        or one greater than the interrupt-nesting depth otherwise.
+        The number after the second "/" is the NMI nesting depth.
 
         This field is displayed only for CONFIG_NO_HZ kernels.
 
@@ -104,7 +115,7 @@ o	"df" is the number of times that some other CPU has forced a
 
 o       "of" is the number of times that some other CPU has forced a
         quiescent state on behalf of this CPU due to this CPU being
-        offline.  In a perfect world, this might neve happen, but it
+        offline.  In a perfect world, this might never happen, but it
         turns out that offlining and onlining a CPU can take several grace
         periods, and so there is likely to be an extended period of time
         when RCU believes that the CPU is online when it really is not.
@@ -121,10 +132,78 @@ o	"ql" is the number of RCU callbacks currently residing on
         of what state they are in (new, waiting for grace period to
         start, waiting for grace period to end, ready to invoke).
 
+o       "qs" gives an indication of the state of the callback queue
+        with four characters:
+
+        "N"     Indicates that there are callbacks queued that are not
+                ready to be handled by the next grace period, and thus
+                will be handled by the grace period following the next
+                one.
+
+        "R"     Indicates that there are callbacks queued that are
+                ready to be handled by the next grace period.
+
+        "W"     Indicates that there are callbacks queued that are
+                waiting on the current grace period.
+
+        "D"     Indicates that there are callbacks queued that have
+                already been handled by a prior grace period, and are
+                thus waiting to be invoked.  Note that callbacks in
+                the process of being invoked are not counted here.
+                Callbacks in the process of being invoked are those
+                that have been removed from the rcu_data structures
+                queues by rcu_do_batch(), but which have not yet been
+                invoked.
+
+        If there are no callbacks in a given one of the above states,
+        the corresponding character is replaced by ".".
+
+o       "kt" is the per-CPU kernel-thread state.  The digit preceding
+        the first slash is zero if there is no work pending and 1
+        otherwise.  The character between the first pair of slashes is
+        as follows:
+
+        "S"     The kernel thread is stopped, in other words, all
+                CPUs corresponding to this rcu_node structure are
+                offline.
+
+        "R"     The kernel thread is running.
+
+        "W"     The kernel thread is waiting because there is no work
+                for it to do.
+
+        "O"     The kernel thread is waiting because it has been
+                forced off of its designated CPU or because its
+                ->cpus_allowed mask permits it to run on other than
+                its designated CPU.
+
+        "Y"     The kernel thread is yielding to avoid hogging CPU.
+
+        "?"     Unknown value, indicates a bug.
+
+        The number after the final slash is the CPU that the kthread
+        is actually running on.
+
+o       "ktl" is the low-order 16 bits (in hexadecimal) of the count of
+        the number of times that this CPU's per-CPU kthread has gone
+        through its loop servicing invoke_rcu_cpu_kthread() requests.
+
 o       "b" is the batch limit for this CPU.  If more than this number
         of RCU callbacks is ready to invoke, then the remainder will
         be deferred.
 
+o       "ci" is the number of RCU callbacks that have been invoked for
+        this CPU.  Note that ci+ql is the number of callbacks that have
+        been registered in absence of CPU-hotplug activity.
+
+o       "co" is the number of RCU callbacks that have been orphaned due to
+        this CPU going offline.  These orphaned callbacks have been moved
+        to an arbitrarily chosen online CPU.
+
+o       "ca" is the number of RCU callbacks that have been adopted due to
+        other CPUs going offline.  Note that ci+co-ca+ql is the number of
+        RCU callbacks registered on this CPU.
+
 There is also an rcu/rcudata.csv file with the same information in
 comma-separated-variable spreadsheet format.
 
@@ -157,15 +236,15 @@ o	"gpnum" is the number of grace periods that have started.  It is
 
 The output of "cat rcu/rcuhier" looks as follows, with very long lines:
 
-c=6902 g=6903 s=2 jfq=3 j=72c7 nfqs=13142/nfqsng=0(13142) fqlh=6 oqlen=0
-1/1 .>. 0:127 ^0    
-3/3 .>. 0:35 ^0    0/0 .>. 36:71 ^1    0/0 .>. 72:107 ^2    0/0 .>. 108:127 ^3    
-3/3f .>. 0:5 ^0    2/3 .>. 6:11 ^1    0/0 .>. 12:17 ^2    0/0 .>. 18:23 ^3    0/0 .>. 24:29 ^4    0/0 .>. 30:35 ^5    0/0 .>. 36:41 ^0    0/0 .>. 42:47 ^1    0/0 .>. 48:53 ^2    0/0 .>. 54:59 ^3    0/0 .>. 60:65 ^4    0/0 .>. 66:71 ^5    0/0 .>. 72:77 ^0    0/0 .>. 78:83 ^1    0/0 .>. 84:89 ^2    0/0 .>. 90:95 ^3    0/0 .>. 96:101 ^4    0/0 .>. 102:107 ^5    0/0 .>. 108:113 ^0    0/0 .>. 114:119 ^1    0/0 .>. 120:125 ^2    0/0 .>. 126:127 ^3    
+c=6902 g=6903 s=2 jfq=3 j=72c7 nfqs=13142/nfqsng=0(13142) fqlh=6
+1/1 ..>. 0:127 ^0
+3/3 ..>. 0:35 ^0    0/0 ..>. 36:71 ^1    0/0 ..>. 72:107 ^2    0/0 ..>. 108:127 ^3
+3/3f ..>. 0:5 ^0    2/3 ..>. 6:11 ^1    0/0 ..>. 12:17 ^2    0/0 ..>. 18:23 ^3    0/0 ..>. 24:29 ^4    0/0 ..>. 30:35 ^5    0/0 ..>. 36:41 ^0    0/0 ..>. 42:47 ^1    0/0 ..>. 48:53 ^2    0/0 ..>. 54:59 ^3    0/0 ..>. 60:65 ^4    0/0 ..>. 66:71 ^5    0/0 ..>. 72:77 ^0    0/0 ..>. 78:83 ^1    0/0 ..>. 84:89 ^2    0/0 ..>. 90:95 ^3    0/0 ..>. 96:101 ^4    0/0 ..>. 102:107 ^5    0/0 ..>. 108:113 ^0    0/0 ..>. 114:119 ^1    0/0 ..>. 120:125 ^2    0/0 ..>. 126:127 ^3
 rcu_bh:
-c=-226 g=-226 s=1 jfq=-5701 j=72c7 nfqs=88/nfqsng=0(88) fqlh=0 oqlen=0
-0/1 .>. 0:127 ^0    
-0/3 .>. 0:35 ^0    0/0 .>. 36:71 ^1    0/0 .>. 72:107 ^2    0/0 .>. 108:127 ^3    
-0/3f .>. 0:5 ^0    0/3 .>. 6:11 ^1    0/0 .>. 12:17 ^2    0/0 .>. 18:23 ^3    0/0 .>. 24:29 ^4    0/0 .>. 30:35 ^5    0/0 .>. 36:41 ^0    0/0 .>. 42:47 ^1    0/0 .>. 48:53 ^2    0/0 .>. 54:59 ^3    0/0 .>. 60:65 ^4    0/0 .>. 66:71 ^5    0/0 .>. 72:77 ^0    0/0 .>. 78:83 ^1    0/0 .>. 84:89 ^2    0/0 .>. 90:95 ^3    0/0 .>. 96:101 ^4    0/0 .>. 102:107 ^5    0/0 .>. 108:113 ^0    0/0 .>. 114:119 ^1    0/0 .>. 120:125 ^2    0/0 .>. 126:127 ^3
+c=-226 g=-226 s=1 jfq=-5701 j=72c7 nfqs=88/nfqsng=0(88) fqlh=0
+0/1 ..>. 0:127 ^0
+0/3 ..>. 0:35 ^0    0/0 ..>. 36:71 ^1    0/0 ..>. 72:107 ^2    0/0 ..>. 108:127 ^3
+0/3f ..>. 0:5 ^0    0/3 ..>. 6:11 ^1    0/0 ..>. 12:17 ^2    0/0 ..>. 18:23 ^3    0/0 ..>. 24:29 ^4    0/0 ..>. 30:35 ^5    0/0 ..>. 36:41 ^0    0/0 ..>. 42:47 ^1    0/0 ..>. 48:53 ^2    0/0 ..>. 54:59 ^3    0/0 ..>. 60:65 ^4    0/0 ..>. 66:71 ^5    0/0 ..>. 72:77 ^0    0/0 ..>. 78:83 ^1    0/0 ..>. 84:89 ^2    0/0 ..>. 90:95 ^3    0/0 ..>. 96:101 ^4    0/0 ..>. 102:107 ^5    0/0 ..>. 108:113 ^0    0/0 ..>. 114:119 ^1    0/0 ..>. 120:125 ^2    0/0 ..>. 126:127 ^3
 
 This is once again split into "rcu_sched" and "rcu_bh" portions,
 and CONFIG_TREE_PREEMPT_RCU kernels will again have an additional
@@ -180,7 +259,7 @@ o	"s" is the "signaled" state that drives force_quiescent_state()'s
 
 o       "jfq" is the number of jiffies remaining for this grace period
         before force_quiescent_state() is invoked to help push things
-        along.  Note that CPUs in dyntick-idle mode thoughout the grace
+        along.  Note that CPUs in dyntick-idle mode throughout the grace
         period will not report on their own, but rather must be check by
         some other CPU via force_quiescent_state().
 
@@ -201,11 +280,6 @@ o	"fqlh" is the number of calls to force_quiescent_state() that
         exited immediately (without even being counted in nfqs above)
         due to contention on ->fqslock.
 
-o       "oqlen" is the number of callbacks on the "orphan" callback
-        list.  RCU callbacks are placed on this list by CPUs going
-        offline, and are "adopted" either by the CPU helping the outgoing
-        CPU or by the next rcu_barrier*() call, whichever comes first.
-
 o       Each element of the form "1/1 0:127 ^0" represents one struct
         rcu_node.  Each line represents one level of the hierarchy, from
         root to leaves.  It is best to think of the rcu_data structures
@@ -229,13 +303,20 @@ o	Each element of the form "1/1 0:127 ^0" represents one struct
                 current grace period.
 
         o       The characters separated by the ">" indicate the state
-                of the blocked-tasks lists.  A "T" preceding the ">"
+                of the blocked-tasks lists.  A "G" preceding the ">"
                 indicates that at least one task blocked in an RCU
                 read-side critical section blocks the current grace
-                period, while a "." preceding the ">" indicates otherwise.
-                The character following the ">" indicates similarly for
-                the next grace period.  A "T" should appear in this
-                field only for rcu-preempt.
+                period, while a "E" preceding the ">" indicates that
+                at least one task blocked in an RCU read-side critical
+                section blocks the current expedited grace period.
+                A "T" character following the ">" indicates that at
+                least one task is blocked within an RCU read-side
+                critical section, regardless of whether any current
+                grace period (expedited or normal) is inconvenienced.
+                A "." character appears if the corresponding condition
+                does not hold, so that "..>." indicates that no tasks
+                are blocked.  In contrast, "GE>T" indicates maximal
+                inconvenience from blocked tasks.
 
         o       The numbers separated by the ":" are the range of CPUs
                 served by this struct rcu_node.  This can be helpful
@@ -315,3 +396,222 @@ o	"nn" is the number of times that this CPU needed nothing.  Alert
         readers will note that the rcu "nn" number for a given CPU very
         closely matches the rcu_bh "np" number for that same CPU.  This
         is due to short-circuit evaluation in rcu_pending().
+
+
+The output of "cat rcu/rcutorture" looks as follows:
+
+rcutorture test sequence: 0 (test in progress)
+rcutorture update version number: 615
+
+The first line shows the number of rcutorture tests that have completed
+since boot.  If a test is currently running, the "(test in progress)"
+string will appear as shown above.  The second line shows the number of
+update cycles that the current test has started, or zero if there is
+no test in progress.
+
+
+The output of "cat rcu/rcuboost" looks as follows:
+
+0:5 tasks=.... kt=W ntb=0 neb=0 nnb=0 j=2f95 bt=300f
+     balk: nt=0 egt=989 bt=0 nb=0 ny=0 nos=16
+6:7 tasks=.... kt=W ntb=0 neb=0 nnb=0 j=2f95 bt=300f
+     balk: nt=0 egt=225 bt=0 nb=0 ny=0 nos=6
+
+This information is output only for rcu_preempt.  Each two-line entry
+corresponds to a leaf rcu_node strcuture.  The fields are as follows:
+
+o       "n:m" is the CPU-number range for the corresponding two-line
+        entry.  In the sample output above, the first entry covers
+        CPUs zero through five and the second entry covers CPUs 6
+        and 7.
+
+o       "tasks=TNEB" gives the state of the various segments of the
+        rnp->blocked_tasks list:
+
+        "T"     This indicates that there are some tasks that blocked
+                while running on one of the corresponding CPUs while
+                in an RCU read-side critical section.
+
+        "N"     This indicates that some of the blocked tasks are preventing
+                the current normal (non-expedited) grace period from
+                completing.
+
+        "E"     This indicates that some of the blocked tasks are preventing
+                the current expedited grace period from completing.
+
+        "B"     This indicates that some of the blocked tasks are in
+                need of RCU priority boosting.
+
+        Each character is replaced with "." if the corresponding
+        condition does not hold.
+
+o       "kt" is the state of the RCU priority-boosting kernel
+        thread associated with the corresponding rcu_node structure.
+        The state can be one of the following:
+
+        "S"     The kernel thread is stopped, in other words, all
+                CPUs corresponding to this rcu_node structure are
+                offline.
+
+        "R"     The kernel thread is running.
+
+        "W"     The kernel thread is waiting because there is no work
+                for it to do.
+
+        "Y"     The kernel thread is yielding to avoid hogging CPU.
+
+        "?"     Unknown value, indicates a bug.
+
+o       "ntb" is the number of tasks boosted.
+
+o       "neb" is the number of tasks boosted in order to complete an
+        expedited grace period.
+
+o       "nnb" is the number of tasks boosted in order to complete a
+        normal (non-expedited) grace period.  When boosting a task
+        that was blocking both an expedited and a normal grace period,
+        it is counted against the expedited total above.
+
+o       "j" is the low-order 16 bits of the jiffies counter in
+        hexadecimal.
+
+o       "bt" is the low-order 16 bits of the value that the jiffies
+        counter will have when we next start boosting, assuming that
+        the current grace period does not end beforehand.  This is
+        also in hexadecimal.
+
+o       "balk: nt" counts the number of times we didn't boost (in
+        other words, we balked) even though it was time to boost because
+        there were no blocked tasks to boost.  This situation occurs
+        when there is one blocked task on one rcu_node structure and
+        none on some other rcu_node structure.
+
+o       "egt" counts the number of times we balked because although
+        there were blocked tasks, none of them were blocking the
+        current grace period, whether expedited or otherwise.
+
+o       "bt" counts the number of times we balked because boosting
+        had already been initiated for the current grace period.
+
+o       "nb" counts the number of times we balked because there
+        was at least one task blocking the current non-expedited grace
+        period that never had blocked.  If it is already running, it
+        just won't help to boost its priority!
+
+o       "ny" counts the number of times we balked because it was
+        not yet time to start boosting.
+
+o       "nos" counts the number of times we balked for other
+        reasons, e.g., the grace period ended first.
+
+
+CONFIG_TINY_RCU and CONFIG_TINY_PREEMPT_RCU debugfs Files and Formats
+
+These implementations of RCU provides a single debugfs file under the
+top-level directory RCU, namely rcu/rcudata, which displays fields in
+rcu_bh_ctrlblk, rcu_sched_ctrlblk and, for CONFIG_TINY_PREEMPT_RCU,
+rcu_preempt_ctrlblk.
+
+The output of "cat rcu/rcudata" is as follows:
+
+rcu_preempt: qlen=24 gp=1097669 g197/p197/c197 tasks=...
+             ttb=. btg=no ntb=184 neb=0 nnb=183 j=01f7 bt=0274
+             normal balk: nt=1097669 gt=0 bt=371 b=0 ny=25073378 nos=0
+             exp balk: bt=0 nos=0
+rcu_sched: qlen: 0
+rcu_bh: qlen: 0
+
+This is split into rcu_preempt, rcu_sched, and rcu_bh sections, with the
+rcu_preempt section appearing only in CONFIG_TINY_PREEMPT_RCU builds.
+The last three lines of the rcu_preempt section appear only in
+CONFIG_RCU_BOOST kernel builds.  The fields are as follows:
+
+o       "qlen" is the number of RCU callbacks currently waiting either
+        for an RCU grace period or waiting to be invoked.  This is the
+        only field present for rcu_sched and rcu_bh, due to the
+        short-circuiting of grace period in those two cases.
+
+o       "gp" is the number of grace periods that have completed.
+
+o       "g197/p197/c197" displays the grace-period state, with the
+        "g" number being the number of grace periods that have started
+        (mod 256), the "p" number being the number of grace periods
+        that the CPU has responded to (also mod 256), and the "c"
+        number being the number of grace periods that have completed
+        (once again mode 256).
+
+        Why have both "gp" and "g"?  Because the data flowing into
+        "gp" is only present in a CONFIG_RCU_TRACE kernel.
+
+o       "tasks" is a set of bits.  The first bit is "T" if there are
+        currently tasks that have recently blocked within an RCU
+        read-side critical section, the second bit is "N" if any of the
+        aforementioned tasks are blocking the current RCU grace period,
+        and the third bit is "E" if any of the aforementioned tasks are
+        blocking the current expedited grace period.  Each bit is "."
+        if the corresponding condition does not hold.
+
+o       "ttb" is a single bit.  It is "B" if any of the blocked tasks
+        need to be priority boosted and "." otherwise.
+
+o       "btg" indicates whether boosting has been carried out during
+        the current grace period, with "exp" indicating that boosting
+        is in progress for an expedited grace period, "no" indicating
+        that boosting has not yet started for a normal grace period,
+        "begun" indicating that boosting has bebug for a normal grace
+        period, and "done" indicating that boosting has completed for
+        a normal grace period.
+
+o       "ntb" is the total number of tasks subjected to RCU priority boosting
+        periods since boot.
+
+o       "neb" is the number of expedited grace periods that have had
+        to resort to RCU priority boosting since boot.
+
+o       "nnb" is the number of normal grace periods that have had
+        to resort to RCU priority boosting since boot.
+
+o       "j" is the low-order 16 bits of the jiffies counter in hexadecimal.
+
+o       "bt" is the low-order 16 bits of the value that the jiffies counter
+        will have at the next time that boosting is scheduled to begin.
+
+o       In the line beginning with "normal balk", the fields are as follows:
+
+        o       "nt" is the number of times that the system balked from
+                boosting because there were no blocked tasks to boost.
+                Note that the system will balk from boosting even if the
+                grace period is overdue when the currently running task
+                is looping within an RCU read-side critical section.
+                There is no point in boosting in this case, because
+                boosting a running task won't make it run any faster.
+
+        o       "gt" is the number of times that the system balked
+                from boosting because, although there were blocked tasks,
+                none of them were preventing the current grace period
+                from completing.
+
+        o       "bt" is the number of times that the system balked
+                from boosting because boosting was already in progress.
+
+        o       "b" is the number of times that the system balked from
+                boosting because boosting had already completed for
+                the grace period in question.
+
+        o       "ny" is the number of times that the system balked from
+                boosting because it was not yet time to start boosting
+                the grace period in question.
+
+        o       "nos" is the number of times that the system balked from
+                boosting for inexplicable ("not otherwise specified")
+                reasons.  This can actually happen due to races involving
+                increments of the jiffies counter.
+
+o       In the line beginning with "exp balk", the fields are as follows:
+
+        o       "bt" is the number of times that the system balked from
+                boosting because there were no blocked tasks to boost.
+
+        o       "nos" is the number of times that the system balked from
+                 boosting for inexplicable ("not otherwise specified")
+                 reasons.
diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt
index cfaac34c4557..6ef692667e2f 100644
--- a/Documentation/RCU/whatisRCU.txt
+++ b/Documentation/RCU/whatisRCU.txt
@@ -849,6 +849,37 @@ All:  lockdep-checked RCU-protected pointer access
 See the comment headers in the source code (or the docbook generated
 from them) for more information.
 
+However, given that there are no fewer than four families of RCU APIs
+in the Linux kernel, how do you choose which one to use?  The following
+list can be helpful:
+
+a.      Will readers need to block?  If so, you need SRCU.
+
+b.      What about the -rt patchset?  If readers would need to block
+        in an non-rt kernel, you need SRCU.  If readers would block
+        in a -rt kernel, but not in a non-rt kernel, SRCU is not
+        necessary.
+
+c.      Do you need to treat NMI handlers, hardirq handlers,
+        and code segments with preemption disabled (whether
+        via preempt_disable(), local_irq_save(), local_bh_disable(),
+        or some other mechanism) as if they were explicit RCU readers?
+        If so, you need RCU-sched.
+
+d.      Do you need RCU grace periods to complete even in the face
+        of softirq monopolization of one or more of the CPUs?  For
+        example, is your code subject to network-based denial-of-service
+        attacks?  If so, you need RCU-bh.
+
+e.      Is your workload too update-intensive for normal use of
+        RCU, but inappropriate for other synchronization mechanisms?
+        If so, consider SLAB_DESTROY_BY_RCU.  But please be careful!
+
+f.      Otherwise, use RCU.
+
+Of course, this all assumes that you have determined that RCU is in fact
+the right tool for your job.
+
 
 8.  ANSWERS TO QUICK QUIZZES