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Subject[PATCH tip/core/rcu 11/17] rcu: Make __call_rcu() handle invocation from idle
Date
From: "Paul E. McKenney" <paul.mckenney@linaro.org>

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>
---
include/linux/rcupdate.h | 13 ++++---------
kernel/rcutree.c | 15 +++++++++------
2 files changed, 13 insertions(+), 15 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index b4be822..c775e3e 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -257,6 +257,10 @@ 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) */
@@ -268,15 +272,6 @@ 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 cdc101e..7720177 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -584,8 +584,6 @@ 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
*
@@ -603,7 +601,7 @@ 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
@@ -644,9 +642,7 @@ 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
@@ -1901,6 +1897,13 @@ __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);
--
1.7.8


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