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authorLinus Torvalds <torvalds@linux-foundation.org>2010-02-01 10:44:06 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2010-02-01 10:44:06 -0800
commitbdd846678387d1313f689c9d341bd9743c9aa451 (patch)
tree312585e17b3fbf2f334f892db1a487e1716ae6ab /kernel
parent935cc9323ac33bb9b6cb853815e5c86f77e50607 (diff)
parent7b7422a566aa0dc1e582ce263d4c7ff4a772700a (diff)
Merge branch 'timers-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
* 'timers-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: clocksource: Prevent potential kgdb dead lock
Diffstat (limited to 'kernel')
-rw-r--r--kernel/time/clocksource.c18
1 files changed, 15 insertions, 3 deletions
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index e85c23404d3..13700833c18 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -343,7 +343,19 @@ static void clocksource_resume_watchdog(void)
{
unsigned long flags;
- spin_lock_irqsave(&watchdog_lock, flags);
+ /*
+ * We use trylock here to avoid a potential dead lock when
+ * kgdb calls this code after the kernel has been stopped with
+ * watchdog_lock held. When watchdog_lock is held we just
+ * return and accept, that the watchdog might trigger and mark
+ * the monitored clock source (usually TSC) unstable.
+ *
+ * This does not affect the other caller clocksource_resume()
+ * because at this point the kernel is UP, interrupts are
+ * disabled and nothing can hold watchdog_lock.
+ */
+ if (!spin_trylock_irqsave(&watchdog_lock, flags))
+ return;
clocksource_reset_watchdog();
spin_unlock_irqrestore(&watchdog_lock, flags);
}
@@ -458,8 +470,8 @@ void clocksource_resume(void)
* clocksource_touch_watchdog - Update watchdog
*
* Update the watchdog after exception contexts such as kgdb so as not
- * to incorrectly trip the watchdog.
- *
+ * to incorrectly trip the watchdog. This might fail when the kernel
+ * was stopped in code which holds watchdog_lock.
*/
void clocksource_touch_watchdog(void)
{