linux-kernel - Re: [PATCH 2/3] watchdog: control hard lockup detection default

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Message-ID: <20140730170719.GF7959@redhat.com>
Date:	Wed, 30 Jul 2014 13:07:19 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Andrew Jones <drjones@...hat.com>,
	Ulrich Obergfell <uobergfe@...hat.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	akpm@...ux-foundation.org, mingo@...hat.com
Subject: Re: [PATCH 2/3] watchdog: control hard lockup detection default

On Wed, Jul 30, 2014 at 04:16:38PM +0200, Paolo Bonzini wrote:
> Il 30/07/2014 15:43, Don Zickus ha scritto:
> >> > Nice catch. Looks like this will need a v2. Paolo, do we have a
> >> > consensus on the proc echoing? Or should that be revisited in the v2 as
> >> > well?
> > As discussed privately, how about something like this to handle that case:
> > (applied on top of these patches)
> 
> Don, what do you think about proc?
> 
> My opinion is still what I mentioned earlier in the thread, i.e. that if
> the file says "1", writing "0" and then "1" should not constitute a
> change WRT to the initial state.
> 

I can agree.  The problem is there are two things this proc value
controls, softlockup and hardlockup.  I have always tried to keep the both
disabled or enabled together.

This patchset tries to separate them for an edge case.  Hence the proc
value becomes slightly confusing.

I don't know the right way to solve this without introducing more proc
values.

We have /proc/sys/kernel/nmi_watchdog and /proc/sys/kernel/watchdog which
point to the same internal variable.  Do I separate them and have
'nmi_watchdog' just mean hardlockup and 'watchdog' mean softlockup?  Then
we can be clear on what the output is.  Or does 'watchdog' represent a
superset of 'nmi_watchdog' && softlockup?

That is where the confusion lies.

Cheers,
Don

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