Commit 1772947b authored Aug 12, 2014 by Paul E. McKenney

rcu: Handle NOCB callbacks from irq-disabled idle code

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@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Paul Gortmaker <paul.gortmaker@windriver.com>

parent 39953dfd

kernel/rcu/tree_plugin.h

+11 −0

Original line number	Diff line number	Diff line
		@@ -2129,6 +2129,17 @@ static bool __call_rcu_nocb(struct rcu_data rdp, struct rcu_head rhp,
		trace_rcu_callback(rdp->rsp->name, rhp,
		-atomic_long_read(&rdp->nocb_q_count_lazy),
		-atomic_long_read(&rdp->nocb_q_count));

		/*
		* 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;
		}