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>

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 31568c73452592c0b1c00699a8e66cdadb5036c4..26f6417f0264f75c2d91f7b71097b7ef168e7626 100644 (file)
--- 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_);

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 89addada3e3ae41968bc02388f44bbd131a7e536..a4a9c916ad3639bca768fb9ddb011e48c825cc0c 100644 (file)
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -585,8 +585,6 @@ void rcu_nmi_exit(void)
        WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
 }
 
-#ifdef CONFIG_PROVE_RCU
-
 /**
  * rcu_is_cpu_idle - see if RCU thinks that the current CPU is idle
  *
@@ -604,7 +602,7 @@ int rcu_is_cpu_idle(void)
 }
 EXPORT_SYMBOL(rcu_is_cpu_idle);
 
-#ifdef CONFIG_HOTPLUG_CPU
+#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
 
 /*
  * Is the current CPU online?  Disable preemption to avoid false positives
@@ -645,9 +643,7 @@ bool rcu_lockdep_current_cpu_online(void)
 }
 EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
 
-#endif /* #ifdef CONFIG_HOTPLUG_CPU */
-
-#endif /* #ifdef CONFIG_PROVE_RCU */
+#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
 
 /**
  * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
@@ -1904,6 +1900,13 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
        else
                trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen);
 
+       /*
+        * If called from an extended quiescent state, invoke the RCU
+        * core in order to force a re-evaluation of RCU's idleness.
+        */
+       if (rcu_is_cpu_idle())
+               invoke_rcu_core();
+
        /* If interrupts were disabled, don't dive into RCU core. */
        if (irqs_disabled_flags(flags)) {
                local_irq_restore(flags);