linux-kernel - Re: [PATCH v3] watchdog: Add hook for kicking in kdump path

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Date:	Wed, 17 Apr 2013 20:03:03 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Don Zickus <dzickus@...hat.com>, linux-watchdog@...r.kernel.org,
	kexec@...ts.infradead.org, wim@...ana.be,
	LKML <linux-kernel@...r.kernel.org>, vgoyal@...hat.com,
	dyoung@...hat.com
Subject: Re: [PATCH v3] watchdog: Add hook for kicking in kdump path

On Wed, Apr 17, 2013 at 02:49:59PM -0700, Eric W. Biederman wrote:
> Don Zickus <dzickus@...hat.com> writes:
> 
> > A common problem with kdump is that during the boot up of the
> > second kernel, the hardware watchdog times out and reboots the
> > machine before a vmcore can be captured.
> >
> > Instead of tellling customers to disable their hardware watchdog
> > timers, I hacked up a hook to put in the kdump path that provides
> > one last kick before jumping into the second kernel.
> >
> > The assumption is the watchdog timeout is at least 10-30 seconds
> > long, enough to get the second kernel to userspace to kick the watchdog
> > again, if needed.
> 
> Why not double the watchdog timeout? and/or pet the watchdog a little
> more frequently.
> 
> This is the least icky hook I have seen proposed to be put on the kexec
> on panic path, but I still suspect this may reduce the ability to take a
> crash dump.  What happens if it was the watchdog timer that panic'd for
> example.
> 
That should be addressed by the use of mutex_trylock(), which should fail in
that case.

Guenter
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