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clockevents: prevent endless loop in tick_handle_periodic()

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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
This commit is contained in:
john stultz 2009-05-01 13:10:25 -07:00 committed by Thomas Gleixner
parent 091438dd56
commit 74a03b69d1
1 changed files with 11 additions and 1 deletions
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12
kernel/time/tick-common.c
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@ -93,7 +93,17 @@ void tick_handle_periodic(struct clock_event_device *dev)
for (;;) {
if (!clockevents_program_event(dev, next, ktime_get()))
return;
tick_periodic(cpu);
/*
* 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);
}
}