path: root/kernel
diff options
authorBen Zhang <benzh@chromium.org>2014-04-03 14:47:18 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-04-03 16:20:58 -0700
commit62572e29bc530b38921ef6059088b4788a9832a5 (patch)
tree1da2d3feddf55f007b0fe6e9db68bbbfbd265f78 /kernel
parent45d4f855046631d63dab8832ba8a8369ed8e04bd (diff)
kernel/watchdog.c: touch_nmi_watchdog should only touch local cpu not every one
I ran into a scenario where while one cpu was stuck and should have panic'd because of the NMI watchdog, it didn't. The reason was another cpu was spewing stack dumps on to the console. Upon investigation, I noticed that when writing to the console and also when dumping the stack, the watchdog is touched. This causes all the cpus to reset their NMI watchdog flags and the 'stuck' cpu just spins forever. This change causes the semantics of touch_nmi_watchdog to be changed slightly. Previously, I accidentally changed the semantics and we noticed there was a codepath in which touch_nmi_watchdog could be touched from a preemtible area. That caused a BUG() to happen when CONFIG_DEBUG_PREEMPT was enabled. I believe it was the acpi code. My attempt here re-introduces the change to have the touch_nmi_watchdog() code only touch the local cpu instead of all of the cpus. But instead of using __get_cpu_var(), I use the __raw_get_cpu_var() version. This avoids the preemption problem. However my reasoning wasn't because I was trying to be lazy. Instead I rationalized it as, well if preemption is enabled then interrupts should be enabled to and the NMI watchdog will have no reason to trigger. So it won't matter if the wrong cpu is touched because the percpu interrupt counters the NMI watchdog uses should still be incrementing. Don said: : I'm ok with this patch, though it does alter the behaviour of how : touch_nmi_watchdog works. For the most part I don't think most callers : need to touch all of the watchdogs (on each cpu). Perhaps a corner case : will pop up (the scheduler?? to mimic touch_all_softlockup_watchdogs() ). : : But this does address an issue where if a system is locked up and one cpu : is spewing out useful debug messages (or error messages), the hard lockup : will fail to go off. We have seen this on RHEL also. Signed-off-by: Don Zickus <dzickus@redhat.com> Signed-off-by: Ben Zhang <benzh@chromium.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
1 files changed, 8 insertions, 8 deletions
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 01c6f979486..e90089fd78e 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -158,14 +158,14 @@ void touch_all_softlockup_watchdogs(void)
void touch_nmi_watchdog(void)
- if (watchdog_user_enabled) {
- unsigned cpu;
- for_each_present_cpu(cpu) {
- if (per_cpu(watchdog_nmi_touch, cpu) != true)
- per_cpu(watchdog_nmi_touch, cpu) = true;
- }
- }
+ /*
+ * Using __raw here because some code paths have
+ * preemption enabled. If preemption is enabled
+ * then interrupts should be enabled too, in which
+ * case we shouldn't have to worry about the watchdog
+ * going off.
+ */
+ __raw_get_cpu_var(watchdog_nmi_touch) = true;