[PATCH 3/4] kgdb,clocksource: Prevent kernel hang in kernel debugger
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From: Jason Wessel on 25 Jan 2010 23:30 This is a regression fix against: 0f8e8ef7c204988246da5a42d576b7fa5277a8e4 Spin locks were added to the clocksource_resume_watchdog() which cause the kernel debugger to deadlock on an SMP system frequently. The kernel debugger can try for the lock, but if it fails it should continue to touch the clocksource watchdog anyway, else it will trip if the general kernel execution has been paused for too long. This introduces an possible race condition where the kernel debugger might not process the list correctly if a clocksource is being added or removed at the time of this call. This race is sufficiently rare vs having the kernel debugger hang the kernel CC: Thomas Gleixner <tglx(a)linutronix.de> CC: Martin Schwidefsky <schwidefsky(a)de.ibm.com> CC: John Stultz <johnstul(a)us.ibm.com> CC: Andrew Morton <akpm(a)linux-foundation.org> CC: Magnus Damm <damm(a)igel.co.jp> Signed-off-by: Jason Wessel <jason.wessel(a)windriver.com> --- kernel/time/clocksource.c | 7 ++++++- 1 files changed, 6 insertions(+), 1 deletions(-) diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index e85c234..74f9ba6 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -463,7 +463,12 @@ void clocksource_resume(void) */ void clocksource_touch_watchdog(void) { - clocksource_resume_watchdog(); + unsigned long flags; + + int got_lock = spin_trylock_irqsave(&watchdog_lock, flags); + clocksource_reset_watchdog(); + if (got_lock) + spin_unlock_irqrestore(&watchdog_lock, flags); } /** -- 1.6.3.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |