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, 11 insertions, 4 deletions

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index e1b005918bbb..d3d5fa54f25e 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -99,15 +99,18 @@ long srcu_batches_completed(struct srcu_struct *sp);
  * power mode. This way we can notice an extended quiescent state to
  * other CPUs that started a grace period. Otherwise we would delay any
  * grace period as long as we run in the idle task.
+ *
+ * Similarly, we avoid claiming an SRCU read lock held if the current
+ * CPU is offline.
  */
 static inline int srcu_read_lock_held(struct srcu_struct *sp)
 {
-        if (rcu_is_cpu_idle())
-                return 0;
-
         if (!debug_lockdep_rcu_enabled())
                 return 1;
-
+        if (rcu_is_cpu_idle())
+                return 0;
+        if (!rcu_lockdep_current_cpu_online())
+                return 0;
         return lock_is_held(&sp->dep_map);
 }
 
@@ -169,6 +172,8 @@ static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
         int retval = __srcu_read_lock(sp);
 
         rcu_lock_acquire(&(sp)->dep_map);
+        rcu_lockdep_assert(!rcu_is_cpu_idle(),
+                           "srcu_read_lock() used illegally while idle");
         return retval;
 }
 
@@ -182,6 +187,8 @@ static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
 static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
         __releases(sp)
 {
+        rcu_lockdep_assert(!rcu_is_cpu_idle(),
+                           "srcu_read_unlock() used illegally while idle");
         rcu_lock_release(&(sp)->dep_map);
         __srcu_read_unlock(sp, idx);
 }