rcu: Make __call_rcu() handle invocation from idle

Although __call_rcu() is handled correctly when called from a momentary
non-idle period, if it is called on a CPU that RCU believes to be idle
on RCU_FAST_NO_HZ kernels, the callback might be indefinitely postponed.
This commit therefore ensures that RCU is aware of the new callback and
has a chance to force the CPU out of dyntick-idle mode when a new callback
is posted.

Reported-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

1 files changed, 4 insertions, 9 deletions

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 31568c734525..26f6417f0264 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -256,6 +256,10 @@ static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
 }
 #endif  /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
 
+#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SMP)
+extern int rcu_is_cpu_idle(void);
+#endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SMP) */
+
 #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
 bool rcu_lockdep_current_cpu_online(void);
 #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
@@ -267,15 +271,6 @@ static inline bool rcu_lockdep_current_cpu_online(void)
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 
-#ifdef CONFIG_PROVE_RCU
-extern int rcu_is_cpu_idle(void);
-#else /* !CONFIG_PROVE_RCU */
-static inline int rcu_is_cpu_idle(void)
-{
-        return 0;
-}
-#endif /* else !CONFIG_PROVE_RCU */
-
 static inline void rcu_lock_acquire(struct lockdep_map *map)
 {
         lock_acquire(map, 0, 0, 2, 1, NULL, _THIS_IP_);