Re: [Xen-users] Watchdog and live migration

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2012-03-16 at 14:34 +0000, Jan Beulich wrote:
> >>> 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?
> 
> Could you give the patch below a try?
> 
> Jan
> 
> --- a/drivers/watchdog/xen_wdt.c
> +++ b/drivers/watchdog/xen_wdt.c
> @@ -297,11 +297,19 @@ static void xen_wdt_shutdown(struct plat
>  
>  static int xen_wdt_suspend(struct platform_device *dev, pm_message_t state)
>  {
> -     return xen_wdt_stop();
> +     typeof(wdt.id) id = wdt.id;

typeof here is a bit odd.

> +     int rc = xen_wdt_stop();
> +
> +     wdt.id = id;
> +
> +     return rc;
>  }
>  
>  static int xen_wdt_resume(struct platform_device *dev)
>  {
> +     if (!wdt.id)
> +             return 0;

Can't you check is_active instead and avoid having to play tricks in
xen_wdt_suspend to preserve a non-0 wdt.id when the watchdog is active?

> +     wdt.id = 0;
>       return xen_wdt_start();
>  }
>  
> 
> 



_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxx
http://lists.xen.org/xen-users