linux-kernel - Re: [PATCH 7/9] watchdog: enable the new user interface of the watchdog mechanism

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Message-ID: <20150224154633.GJ126481@redhat.com>
Date:	Tue, 24 Feb 2015 10:46:33 -0500
From:	Don Zickus <dzickus@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ulrich Obergfell <uobergfe@...hat.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 7/9] watchdog: enable the new user interface of the
 watchdog mechanism

On Mon, Feb 23, 2015 at 01:19:46PM -0800, Andrew Morton wrote:
> On Thu,  5 Feb 2015 15:40:23 -0500 Don Zickus <dzickus@...hat.com> wrote:
> 
> > From: Ulrich Obergfell <uobergfe@...hat.com>
> > 
> > With the current user interface of the watchdog mechanism it is only
> > possible to disable or enable both lockup detectors at the same time.
> > This series introduces new kernel parameters and changes the semantics
> > of some existing kernel parameters, so that the hard lockup detector
> > and the soft lockup detector can be disabled or enabled individually.
> > With this series applied, the user interface is as follows.
> > 
> > - parameters in /proc/sys/kernel
> > 
> >   . soft_watchdog
> >     This is a new parameter to control and examine the run state of
> >     the soft lockup detector.
> > 
> >   . nmi_watchdog
> >     The semantics of this parameter have changed. It can now be used
> >     to control and examine the run state of the hard lockup detector.
> > 
> >   . watchdog
> >     This parameter is still available to control the run state of both
> >     lockup detectors at the same time. If this parameter is examined,
> >     it shows the logical OR of soft_watchdog and nmi_watchdog.
> > 
> >   . watchdog_thresh
> >     The semantics of this parameter are not affected by the patch.
> > 
> > - kernel command line parameters
> > 
> >   . nosoftlockup
> >     The semantics of this parameter have changed. It can now be used
> >     to disable the soft lockup detector at boot time.
> > 
> >   . nmi_watchdog=0 or nmi_watchdog=1
> >     Disable or enable the hard lockup detector at boot time. The patch
> >     introduces '=1' as a new option.
> > 
> >   . nowatchdog
> >     The semantics of this parameter are not affected by the patch. It
> >     is still available to disable both lockup detectors at boot time.
> 
> So we need a whole bunch of updates and additions to Documentation/?

Ok.

> 
> Are all these changes back-compatible with previous kernel versions?

I believe so.  The motivation for some of the change was the ambiguity of
the /proc/sys/kerne/watchdog variable.  This patchset clears that up.  So
if it breaks backward compatibility, it is because it was misinterpreted
from its original intention.

Old definition of the proc/sys/kernel variable:

watchdog  == nmi_watchdog_enabled

New definition:

watchdog == nmi_watchdog_enabled | softlockup_enabled


Cheers,
Don

> 
> 
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