Merge branch 'timers-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel...

[karo-tx-linux.git] / kernel / time / clocksource.c

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index e85c23404d34526acfc9359a530ec23044aa0b7e..13700833c181755f0f5a60e6fe34d53edb96448d 100644 (file)
--- 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)
 {