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Re: [PATCH 08/16] xen/arm: add watchdog domain suspend/resume helpers
- To: Mykola Kvach <xakep.amatop@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 21 Mar 2025 15:04:08 +0100
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- Cc: Mykola Kvach <mykola_kvach@xxxxxxxx>, Dario Faggioli <dfaggioli@xxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, George Dunlap <gwd@xxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Mirela Simonovic <mirela.simonovic@xxxxxxxxxx>, Saeed Nowshadi <saeed.nowshadi@xxxxxxxxxx>, Mykyta Poturai <mykyta_poturai@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Fri, 21 Mar 2025 14:04:13 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 21.03.2025 10:50, Mykola Kvach wrote:
> On Thu, Mar 13, 2025 at 5:34 PM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>> On 05.03.2025 10:11, Mykola Kvach wrote:
>>> +void watchdog_domain_resume(struct domain *d)
>>> +{
>>> + unsigned int i;
>>> +
>>> + spin_lock(&d->watchdog_lock);
>>> +
>>> + for ( i = 0; i < NR_DOMAIN_WATCHDOG_TIMERS; i++ )
>>> + {
>>> + if ( test_bit(i, &d->watchdog_inuse_map) )
>>> + {
>>> + set_timer(&d->watchdog_timer[i].timer,
>>> + NOW() + SECONDS(d->watchdog_timer[i].timeout));
>>
>> The timeout may have almost expired before suspending; restoring to the
>> full original period feels wrong. At the very least, if that's indeed
>> intended behavior, imo this needs spelling out explicitly.
>
> It takes some time to wake up the domain, but the watchdog timeout is
> reset by a userspace daemon. As a result, we can easily encounter a
> watchdog trigger during the resume process.
Which may mean the restoring is done too early, or needs doing in two
phases.
> It looks like we should
> stop the watchdog timer from the guest, and in that case, we can drop
> all changes related to the watchdog in this patch series.
Except that then you require a guest to be aware of host suspend. Which
may not be desirable.
Jan
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