[PATCH tip/core/rcu 13/14] rcu: Handle NOCB callbacks from irq-disabled idle code

From: Paul E. McKenney
Date: Thu Aug 28 2014 - 14:42:03 EST

From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>

If an RCU callback is queued on a no-CBs CPU from idle code with irqs
disabled, and if that CPU stays idle forever after, the callback will
never be invoked. This commit therefore adds a check for this situation
in ____call_rcu_nocb(), invoking the RCU core solely for the purpose
of the ensuing return-to-idle transition. (If the CPU doesn't return
to idle, the next scheduling-clock interrupt will fix things up.)

Reported-by: Amit Shah <amit.shah@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
kernel/rcu/tree_plugin.h | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 304f42c6543b..700e5b37bf26 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2129,6 +2129,17 @@ static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
trace_rcu_callback(rdp->rsp->name, rhp,
+ /*
+ * If called from an extended quiescent state with interrupts
+ * disabled, invoke the RCU core in order to allow the idle-entry
+ * deferred-wakeup check to function.
+ */
+ if (irqs_disabled_flags(flags) &&
+ !rcu_is_watching() &&
+ cpu_online(smp_processor_id()))
+ invoke_rcu_core();
return true;


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