Messages in this thread Patch in this message | | | Date | Wed, 06 May 2009 14:46:20 -0700 | From | Greg KH <> | Subject | [patch 52/58] clockevents: prevent endless loop in tick_handle_periodic() |
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2.6.29-stable review patch. If anyone has any objections, please let us know.
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From: john stultz <johnstul@us.ibm.com>
commit 74a03b69d1b5ce00a568e142ca97e76b7f5239c6 upstream.
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 Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- a/kernel/time/tick-common.c +++ b/kernel/time/tick-common.c @@ -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); } }
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