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SubjectRe: [PATCH v2] watchdog: touch_nmi_watchdog should only touch local cpu not every one
On Mon, Nov 08, 2010 at 07:05:23PM +0100, Frederic Weisbecker wrote:
> On Mon, Nov 08, 2010 at 11:44:35AM -0500, Don Zickus wrote:
> > 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.
> >
> > V2: remove touch_all_nmi_watchdog code
>
>
> Are you sure you did? :)

Hmm.. Odd. I remember making and committing the changes. But now I can't
find them.

Thanks for catching that! I'll send out a version 3.

Cheers,
Don


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