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CHROMIUM: watchdog: touch_nmi_watchdog should only touch local cpu not every one

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This is a patch from Don Zickus. It's not been merged to the upstream yet.

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.

BUG=chromium:305420
TEST=platform_KernelErrorPaths, verified on peppy

Change-Id: I3791d76be7fc13c8bf6d3e21bf6a487ce1f50210
Signed-off-by: Don Zickus <dzickus@redhat.com>
Signed-off-by: Ben Zhang <benzh@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/179418
Reviewed-by: Sameer Nanda <snanda@chromium.org>

[benzh: 3.14 rebase. Resolved trivial conflicts]
Signed-off-by: Ben Zhang <benzh@chromium.org>
This commit is contained in:
Ben Zhang
2013-12-09 15:22:58 -08:00
parent 57d121c1a3
commit f1eee316c6
1 changed files with 8 additions and 8 deletions
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16
kernel/watchdog.c
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@@ -163,14 +163,14 @@ void touch_all_softlockup_watchdogs(void)
#ifdef CONFIG_HARDLOCKUP_DETECTOR
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;
touch_softlockup_watchdog();
}
EXPORT_SYMBOL(touch_nmi_watchdog);