linux-kernel - Re: [PATCH 4/5] watchdog: control hard lockup detection default

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Date:	Mon, 18 Aug 2014 20:07:35 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Don Zickus <dzickus@...hat.com>
Cc:	akpm@...ux-foundation.org, kvm@...r.kernel.org,
	pbonzini@...hat.com, mingo@...hat.com,
	LKML <linux-kernel@...r.kernel.org>,
	Ulrich Obergfell <uobergfe@...hat.com>,
	Andrew Jones <drjones@...hat.com>
Subject: Re: [PATCH 4/5] watchdog: control hard lockup detection default


* Don Zickus <dzickus@...hat.com> wrote:

> On Mon, Aug 18, 2014 at 11:16:44AM +0200, Ingo Molnar wrote:
> > 
> > * Don Zickus <dzickus@...hat.com> wrote:
> > 
> > > The running kernel still has the ability to enable/disable at any
> > > time with /proc/sys/kernel/nmi_watchdog us usual. However even
> > > when the default has been overridden /proc/sys/kernel/nmi_watchdog
> > > will initially show '1'. To truly turn it on one must disable/enable
> > > it, i.e.
> > >   echo 0 > /proc/sys/kernel/nmi_watchdog
> > >   echo 1 > /proc/sys/kernel/nmi_watchdog
> > 
> > This looks like a bug, why is this so?
> 
> It is, but it always has been there in the case of the PMU 
> not being able to provide a resource for the hardlockup.  
> This change just exposes it more.

There seems to be two issues:

1)

When it's impossible to enable the hardlockup detector, it 
should default to -1 or so, and attempts to set it should 
return a -EINVAL or so.

Bootup messages should also indicate when it's not possible to 
enable it but a user requests it.

2)

The softlockup and hardlockup detection control variables 
should be in separate flags, inside and outside the kernel - 
they (should) not relate to each other.

Thanks,

	Ingo
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