Commit 74a03b69 authored May 01, 2009 by john stultz Committed by Thomas Gleixner May 02, 2009

clockevents: prevent endless loop in tick_handle_periodic()



tick_handle_periodic() can lock up hard when a one shot clock event
device is used in combination with jiffies clocksource.

Avoid an endless loop issue by requiring that a highres valid
clocksource be installed before we call tick_periodic() in a loop when
using ONESHOT mode. The result is we will only increment jiffies once
per interrupt until a continuous hardware clocksource is available.

Without this, we can run into a endless loop, where each cycle through
the loop, jiffies is updated which increments time by tick_period or
more (due to clock steering), which can cause the event programming to
think the next event was before the newly incremented time and fail
causing tick_periodic() to be called again and the whole process loops
forever.

[ Impact: prevent hard lock up ]

Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@kernel.org

parent 091438dd

kernel/time/tick-common.c

+11 −1

Original line number	Diff line number	Diff line
		@@ -93,6 +93,16 @@ void tick_handle_periodic(struct clock_event_device *dev)
		for (;;) {
		if (!clockevents_program_event(dev, next, ktime_get()))
		return;
		/*
		* Have to be careful here. If we're in oneshot mode,
		* before we call tick_periodic() in a loop, we need
		* to be sure we're using a real hardware clocksource.
		* Otherwise we could get trapped in an infinite
		* loop, as the tick_periodic() increments jiffies,
		* when then will increment time, posibly causing
		* the loop to trigger again and again.
		*/
		if (timekeeping_valid_for_hres())
		tick_periodic(cpu);
		next = ktime_add(next, tick_period);
		}

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