Re: [Xen-users] Watchdog and live migration

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.03.12 at 13:32, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> I think this is a bug, moving to xen-devel@ and CCing the drivers author
> (Hi Jan).
> 
> On Fri, 2012-03-16 at 12:29 +0000, Wouter de Geus wrote:
>> * Ian Campbell <Ian.Campbell@xxxxxxxxxx> [2012-03-16 10:55:34 +0000]:
>> 
>> > > In the domU a /dev/watchdog exists, but I never touch it myself.
>> > 
>> > Does your distro start a watchdogd for you?
>> > 
>> > Even if it did then it should obviously continue to poke the watchdog
>> > even after a migration, but it might provide some hints.
>> 
>> Nope, it doesn't.
>> As an experiemtn I tried sending a 'V' to /dev/watchdog just after 
>> migration, which seems to be the magic byte to stop the watchdog 
>> according to the linux kernel docs.
>> 
>> (according to Documentation/watchdog/watchdog-api.txt) - 
>> "If a driver supports "Magic Close", the driver will not disable the
>> watchdog unless a specific magic character 'V' has been sent to
>> /dev/watchdog just before closing the file."
>> 
>> Surprisingly, the domU seemed to stay alive after doing this.
>> So it would appear that somehow the watchdog is triggered after migration.
>> No idea why though.
> 
> drivers/watchdog/xen_wdt.c:xen_wdt_resume() unconditionally calls
> xen_wdt_start(). Shouldn't it only do this if the wdt is active?

Oh, yes, of course. I don't really recall what other driver I used
as skeleton, but when adjusting the bits for Xen I obviously screwed
this up. Will get a fix out soon.

Jan


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