From: john stultz Date: Fri, 1 May 2009 20:10:25 +0000 (-0700) Subject: clockevents: prevent endless loop in tick_handle_periodic() X-Git-Tag: v2.6.27.23~5 X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=2ee201a9d57df7a12e228c6a9b06a15014231b72;p=karo-tx-linux.git clockevents: prevent endless loop in tick_handle_periodic() 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 Signed-off-by: Andrew Morton Signed-off-by: Thomas Gleixner Cc: stable@kernel.org Signed-off-by: Greg Kroah-Hartman --- diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c index df12434b43ca..bad22e2a5523 100644 --- 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); } }