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

Pull RCU changes for v3.4 from Ingo Molnar.  The major features of this
series are:

 - making RCU more aggressive about entering dyntick-idle mode in order
   to improve energy efficiency

 - converting a few more call_rcu()s to kfree_rcu()s

 - applying a number of rcutree fixes and cleanups to rcutiny

 - removing CONFIG_SMP #ifdefs from treercu

 - allowing RCU CPU stall times to be set via sysfs

 - adding CPU-stall capability to rcutorture

 - adding more RCU-abuse diagnostics

 - updating documentation

 - fixing yet more issues located by the still-ongoing top-to-bottom
   inspection of RCU, this time with a special focus on the CPU-hotplug
   code path.

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (48 commits)
  rcu: Stop spurious warnings from synchronize_sched_expedited
  rcu: Hold off RCU_FAST_NO_HZ after timer posted
  rcu: Eliminate softirq-mediated RCU_FAST_NO_HZ idle-entry loop
  rcu: Add RCU_NONIDLE() for idle-loop RCU read-side critical sections
  rcu: Allow nesting of rcu_idle_enter() and rcu_idle_exit()
  rcu: Remove redundant check for rcu_head misalignment
  PTR_ERR should be called before its argument is cleared.
  rcu: Convert WARN_ON_ONCE() in rcu_lock_acquire() to lockdep
  rcu: Trace only after NULL-pointer check
  rcu: Call out dangers of expedited RCU primitives
  rcu: Rework detection of use of RCU by offline CPUs
  lockdep: Add CPU-idle/offline warning to lockdep-RCU splat
  rcu: No interrupt disabling for rcu_prepare_for_idle()
  rcu: Move synchronize_sched_expedited() to rcutree.c
  rcu: Check for illegal use of RCU from offlined CPUs
  rcu: Update stall-warning documentation
  rcu: Add CPU-stall capability to rcutorture
  rcu: Make documentation give more realistic rcutorture duration
  rcutorture: Permit holding off CPU-hotplug operations during boot
  rcu: Print scheduling-clock information on RCU CPU stall-warning messages
  ...

1 files changed, 14 insertions, 0 deletions

diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt
index bff2d8be1e18..5c8d74968090 100644
--- a/Documentation/RCU/checklist.txt
+++ b/Documentation/RCU/checklist.txt
@@ -180,6 +180,20 @@ over a rather long period of time, but improvements are always welcome!
 	operations that would not normally be undertaken while a real-time
 	workload is running.
 
+	In particular, if you find yourself invoking one of the expedited
+	primitives repeatedly in a loop, please do everyone a favor:
+	Restructure your code so that it batches the updates, allowing
+	a single non-expedited primitive to cover the entire batch.
+	This will very likely be faster than the loop containing the
+	expedited primitive, and will be much much easier on the rest
+	of the system, especially to real-time workloads running on
+	the rest of the system.
+
+	In addition, it is illegal to call the expedited forms from
+	a CPU-hotplug notifier, or while holding a lock that is acquired
+	by a CPU-hotplug notifier.  Failing to observe this restriction
+	will result in deadlock.
+
 7.	If the updater uses call_rcu() or synchronize_rcu(), then the
 	corresponding readers must use rcu_read_lock() and
 	rcu_read_unlock().  If the updater uses call_rcu_bh() or