Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull RCU changes from Ingo Molar:
 "The main changes:

   - torture-test updates
   - callback-offloading changes
   - maintainership changes
   - update RCU documentation
   - miscellaneous fixes"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (32 commits)
  rcu: Allow for NULL tick_nohz_full_mask when nohz_full= missing
  rcu: Fix a sparse warning in rcu_report_unblock_qs_rnp()
  rcu: Fix a sparse warning in rcu_initiate_boost()
  rcu: Fix __rcu_reclaim() to use true/false for bool
  rcu: Remove CONFIG_PROVE_RCU_DELAY
  rcu: Use __this_cpu_read() instead of per_cpu_ptr()
  rcu: Don't use NMIs to dump other CPUs' stacks
  rcu: Bind grace-period kthreads to non-NO_HZ_FULL CPUs
  rcu: Simplify priority boosting by putting rt_mutex in rcu_node
  rcu: Check both root and current rcu_node when setting up future grace period
  rcu: Allow post-unlock reference for rt_mutex
  rcu: Loosen __call_rcu()'s rcu_head alignment constraint
  rcu: Eliminate read-modify-write ACCESS_ONCE() calls
  rcu: Remove redundant ACCESS_ONCE() from tick_do_timer_cpu
  rcu: Make rcu node arrays static const char * const
  signal: Explain local_irq_save() call
  rcu: Handle obsolete references to TINY_PREEMPT_RCU
  rcu: Document deadlock-avoidance information for rcu_read_unlock()
  scripts: Teach get_maintainer.pl about the new "R:" tag
  rcu: Update rcu torture maintainership filename patterns
  ...

4 files changed, 41 insertions, 6 deletions

diff --git a/Documentation/RCU/RTFP.txt b/Documentation/RCU/RTFP.txt
index 2f0fcb2112d2..f29bcbc463e7 100644
--- a/Documentation/RCU/RTFP.txt
+++ b/Documentation/RCU/RTFP.txt
@@ -2451,8 +2451,8 @@ lot of {Linux} into your technology!!!"
 ,month="February"
 ,year="2010"
 ,note="Available:
-\url{http://kerneltrap.com/mailarchive/linux-netdev/2010/2/26/6270589}
-[Viewed March 20, 2011]"
+\url{http://thread.gmane.org/gmane.linux.network/153338}
+[Viewed June 9, 2014]"
 ,annotation={
         Use a pair of list_head structures to support RCU-protected
         resizable hash tables.
diff --git a/Documentation/RCU/rcuref.txt b/Documentation/RCU/rcuref.txt
index 141d531aa14b..613033ff2b9b 100644
--- a/Documentation/RCU/rcuref.txt
+++ b/Documentation/RCU/rcuref.txt
@@ -1,5 +1,14 @@
 Reference-count design for elements of lists/arrays protected by RCU.
 
+
+Please note that the percpu-ref feature is likely your first
+stop if you need to combine reference counts and RCU.  Please see
+include/linux/percpu-refcount.h for more information.  However, in
+those unusual cases where percpu-ref would consume too much memory,
+please read on.
+
+------------------------------------------------------------------------
+
 Reference counting on elements of lists which are protected by traditional
 reader/writer spinlocks or semaphores are straightforward:
 
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 45fbea7c329b..90f6139608ff 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2813,6 +2813,13 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                         quiescent states.  Units are jiffies, minimum
                         value is one, and maximum value is HZ.
 
+        rcutree.rcu_nocb_leader_stride= [KNL]
+                        Set the number of NOCB kthread groups, which
+                        defaults to the square root of the number of
+                        CPUs.  Larger numbers reduces the wakeup overhead
+                        on the per-CPU grace-period kthreads, but increases
+                        that same overhead on each group's leader.
+
         rcutree.qhimark= [KNL]
                         Set threshold of queued RCU callbacks beyond which
                         batch limiting is disabled.
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index f1dc4a215593..a4de88fb55f0 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -757,10 +757,14 @@ SMP BARRIER PAIRING
 When dealing with CPU-CPU interactions, certain types of memory barrier should
 always be paired.  A lack of appropriate pairing is almost certainly an error.
 
-A write barrier should always be paired with a data dependency barrier or read
-barrier, though a general barrier would also be viable.  Similarly a read
-barrier or a data dependency barrier should always be paired with at least an
-write barrier, though, again, a general barrier is viable:
+General barriers pair with each other, though they also pair with
+most other types of barriers, albeit without transitivity.  An acquire
+barrier pairs with a release barrier, but both may also pair with other
+barriers, including of course general barriers.  A write barrier pairs
+with a data dependency barrier, an acquire barrier, a release barrier,
+a read barrier, or a general barrier.  Similarly a read barrier or a
+data dependency barrier pairs with a write barrier, an acquire barrier,
+a release barrier, or a general barrier:
 
         CPU 1                 CPU 2
         ===============       ===============
@@ -1893,6 +1897,21 @@ between the STORE to indicate the event and the STORE to set TASK_RUNNING:
             <general barrier>             STORE current->state
         LOAD event_indicated
 
+To repeat, this write memory barrier is present if and only if something
+is actually awakened.  To see this, consider the following sequence of
+events, where X and Y are both initially zero:
+
+        CPU 1                           CPU 2
+        =============================== ===============================
+        X = 1;                          STORE event_indicated
+        smp_mb();                       wake_up();
+        Y = 1;                          wait_event(wq, Y == 1);
+        wake_up();                        load from Y sees 1, no memory barrier
+                                        load from X might see 0
+
+In contrast, if a wakeup does occur, CPU 2's load from X would be guaranteed
+to see 1.
+
 The available waker functions include:
 
         complete();