Re: [Xen-users] Watchdog and live migration

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

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?

Ian.



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