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Date: Wed, 2 Jun 2010 21:13:40 +0200
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Don Zickus <dzickus@redhat.com>
Cc: Jiri Slaby <jirislaby@gmail.com>, LKML <linux-kernel@vger.kernel.org>,
       Linux-pm mailing list <linux-pm@lists.linux-foundation.org>,
       linux-ide@vger.kernel.org
Subject: Re: hibernation hangs with ATA errors (lockup_detector bug)
Message-ID: <20100602191336.GA5164@nowhere>
References: <4C03C608.1040600@gmail.com> <20100601135004.GP15159@redhat.com> <4C051D44.7040203@gmail.com> <20100602184459.GA15159@redhat.com>
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On Wed, Jun 02, 2010 at 02:44:59PM -0400, Don Zickus wrote:
> On Tue, Jun 01, 2010 at 04:46:28PM +0200, Jiri Slaby wrote:
> > On 06/01/2010 03:50 PM, Don Zickus wrote:
> > > On Mon, May 31, 2010 at 04:22:00PM +0200, Jiri Slaby wrote:
> > >> Hi,
> > >>
> > >> with -next I get the following errors while trying to hibernate in
> > >> qemu-kvm after the image is stored on disk:
> > > 
> > > Is this the host that is hibernating or the guest?
> > 
> > Guest.
> > 
> > > KVM guests don't emulate the performance counters, so the nmi piece
> > > shouldn't be functioning and the soft lockup piece just sits on top of an
> > > hrtimer, so off the top of my head it is hard to imagine it intefering
> > > with a sata driver.
> > > 
> > > I'll need your whole boot up log to see how the lockup detector
> > > initialized itself.
> 
> Ok, so I found out what is causing the problem, not entirely sure why or
> what the right fix is, but this patch should do the trick.
> 
> This is probably one of those fixing the symptoms but not the problem patch,
> but I don't know enough about suspend/resume to understand what the real
> problem is.


So the problem is that we stop the cpu hotplug notifying, I guess this prevents
some ata callbacks to execute in the cpu hotplug notifier and then provoke this
crash.

The patch looks ok, but I think you should at least print a message in such
case of watchdog failure.

Thanks.


> 
> ---->SNIP<---------------------
> [lockup detector] don't return NOTIFY_BAD when cpu goes online for suspend
> 
> KVM guests do not support performance counter emulation, so if the nmi
> watchdog piece is compiled in, it will always fail during boot.  The
> failure returns NOTIFY_BAD when the cpu goes online in the cpu notifier
> callback.  Returning NOTIFY_BAD causes hibernation to do really bad
> things, so avoid doing that.
> 
> The cpu failure shouldn't be a critical failure anyway, so returning
> NOTIFY_BAD was probably overstating things.
> 
> Signed-off-by: Don Zickus <dzickus@redhat.com>
> 
> 
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> index 6b7fad8..fda9770 100644
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -550,8 +550,7 @@ cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
>  		break;
>  	case CPU_ONLINE:
>  	case CPU_ONLINE_FROZEN:
> -		if (watchdog_enable(hotcpu))
> -			return NOTIFY_BAD;
> +		watchdog_enable(hotcpu)
>  		break;
>  #ifdef CONFIG_HOTPLUG_CPU
>  	case CPU_UP_CANCELED:

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