Commit 79b9a75f authored Apr 23, 2012 by Paul E. McKenney Committed by Paul E. McKenney Apr 26, 2012

rcu: Add warning for RCU_FAST_NO_HZ timer firing

RCU_FAST_NO_HZ uses a timer to limit the time that a CPU with callbacks
can remain in dyntick-idle mode. This timer is cancelled when the CPU
exits idle, and therefore should never fire. However, if the timer
were migrated to some other CPU for whatever reason (1) the timer could
actually fire and (2) firing on some other CPU would fail to wake up the
CPU with callbacks, possibly resulting in sluggishness or a system hang.

This commit therfore adds a WARN_ON_ONCE() to the timer handler in order
to detect this condition.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

parent c57afe80

kernel/rcutree_plugin.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -2065,6 +2065,7 @@ static bool rcu_cpu_has_nonlazy_callbacks(int cpu)
		*/
		static void rcu_idle_gp_timer_func(unsigned long unused)
		{
		WARN_ON_ONCE(1); /* Getting here can hang the system... */
		trace_rcu_prep_idle("Timer");
		}

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