Re: "default" watchdog device - ?

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On Wed, Mar 16, 2022 at 1:55 PM lejeczek <peljasz@xxxxxxxxxxx> wrote:
> On 15/03/2022 11:21, Daniel P. Berrangé wrote:
> > On Tue, Mar 15, 2022 at 10:39:50AM +0000, lejeczek wrote:
> >> Hi guys.
> >>
> >> Without explicitly, manually using watchdog device for a VM, the VM (centOS
> >> 8 Stream 4.18.0-365.el8.x86_64) shows '/dev/watchdog' exists.
> >> To double check - 'dumpxml' does not show any such device - what kind of a
> >> 'watchdog' that is?
> > The kernel can always provide a pure software watchdog IIRC. It can be
> > useful if a userspace app wants a watchdog. The limitation is that it
> > relies on the kernel remaining functional, as there's no hardware
> > backing it up.
> >
> > Regards,
> > Daniel
> On a related note - with 'i6300esb' watchdog which I tested
> and I believe is working.
> I get often in my VMs from 'dmesg':
> ...
> watchdog: BUG: soft lockup - CPU#0 stuck for xxxs! [swapper/0:0]
> rcu: INFO: rcu_sched self-detected stall on CPU
> ...
> This above is from Ubuntu and CentOS alike and when this
> happens, console via VNC responds to until first 'enter'
> then is non-resposive.
> This happens after VM(s) was migrated between hosts, but
> anyway..
> I do not see what I expected from 'watchdog' - there is no
> action whatsoever, which should be 'reset'. VM remains in
> such 'frozen' state forever.
> any & all shared thoughts much appreciated.
> L.

You need to run some userspace tool that will open the watchdog
device, and pet it periodically, telling the kernel that userspace is alive.

If this tool will stop petting the watchdog, maybe because of a soft lockup
or other trouble, the watchdog device will reset the VM.

watchdog(8) may be the tool you need.

See also


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