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SubjectRe: [PATCH 1/2 v2] watchdog, nmi: Allow hardlockup to panic by default
On Thu, Mar 17, 2011 at 06:50:13PM -0700, Andrew Morton wrote:
> On Mon, 7 Mar 2011 16:37:39 -0500 Don Zickus <dzickus@redhat.com> wrote:
>
> > Add a Kconfig option to allow users to set the hardlockup to panic
> > by default. Also add in a 'nmi_watchdog=nopanic' to override this.
> >
>
> Changelog forgot to tell us "why".

Yeah, sorry about that.

When a cpu is considered stuck, instead of limping along and just printing
a warning, it is sometimes preferred to just panic, let kdump capture the
vmcore and reboot. This gets the machine back into a stable state quickly
while saving the info that got it into a stuck state to begin with.


>
> > Format: [state][,regs][,debounce][,die]
> >
> > nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
> > - Format: [panic,][num]
> > + Format: [panic,][nopanic,][num]
>
> It would be better to support panic=[0|1], if that can be simply done
> in a back-compatible fashion.

I am open to the idea, just can't figure the best way to implement that in
a backwards compatible way.

Personally I was wondering if there were situations where you would _not_
want it to panic. If the cpu is stuck spinning after 60 seconds, the odds
of it freeing itself is low and you are probably stuck rebooting anyway.


>
> > static int __init hardlockup_panic_setup(char *str)
> > {
> > if (!strncmp(str, "panic", 5))
> > hardlockup_panic = 1;
> > + else if (!strncmp(str, "nopanic", 5))
>
> s/5/7/

doh.

I can send a refreshed patch with the above changes.

Cheers,
Don


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