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

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Message-ID: <20130418174432.GN79013@redhat.com>
Date:	Thu, 18 Apr 2013 13:44:32 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	linux-watchdog@...r.kernel.org, kexec@...ts.infradead.org,
	wim@...ana.be, LKML <linux-kernel@...r.kernel.org>,
	vgoyal@...hat.com, dyoung@...hat.com,
	Guenter Roeck <linux@...ck-us.net>
Subject: Re: [PATCH v3] watchdog: Add hook for kicking in kdump path

On Thu, Apr 18, 2013 at 09:35:05AM -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.
> 
> Having thought about this a little more this patch is actively wrong.
> 
> The problem is you can easily be petting the watchdog in violation of
> whatever policy is normally in place.  Which means that this extra
> petting can result in a system that is unavailable for an unacceptably
> long period of time.

Not really, just an extra period which isn't that much.  This would only
be noticable if kdump is setup and enabled and then _hung_, otherwise it
just quickly reboots and noone notices. :-)

> 
> I expect most watchdog policies are not that strict, but this patch
> would preclude using those that are.

I would assume most of those users would not enable kdump and would not be
affected.

> 
> And like is being discussed in another subthread it does look like
> changing the timeout and the interval should be enough all on it's own.

Probably and I will pursue that.  Thanks for the suggestion.

Cheers,
Don
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