Re: [PATCH v2 1/2] xl: Keep monitoring suspended domain

[Jason Andryuk <jason.andryuk@xxxxxxx>]

On 2024-12-02 03:53, Jan Beulich wrote:
> On 28.11.2024 17:45, Anthony PERARD wrote:
> > On Tue, Nov 26, 2024 at 12:19:40PM -0500, Jason Andryuk wrote:
> > > When a VM transitioned to LIBXL_SHUTDOWN_REASON_SUSPEND, the xl daemon
> > > was exiting as 0 = DOMAIN_RESTART_NONE "No domain restart".
> > > Later, when the VM actually shutdown, the missing xl daemon meant the
> > > domain wasn't cleaned up properly.
> > >
> > > Add a new DOMAIN_RESTART_SUSPENDED to handle the case.  The xl daemon
> > > keeps running to react to future shutdown events.
> > >
> > > The domain death event needs to be re-enabled to catch subsequent
> > > events.  The libxl_evgen_domain_death is moved from death_list to
> > > death_reported, and then it isn't found on subsequent iterations through
> > > death_list.  We enable the new event before disabling the old event, to
> > > keep the xenstore watch active.  If it is unregistered and
> > > re-registered, it'll fire immediately for our suspended domain which
> > > will end up continuously re-triggering.
> > >
> > > Signed-off-by: Jason Andryuk <jason.andryuk@xxxxxxx>
> > Reviewed-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
> While committing I was wondering: Does this want/need backporting (and hence
> was it perhaps lacking a Fixes: tag)?
Thanks, Jan.

I don't think it's really worth backporting.  Mainly, it hasn't been an 
issue in the last 14 years.  A Linux domU doesn't suspend itself - it 
only does so in response to a xenstore watch.  A domU *could* suspend 
itself without the xenstore watch, but that doesn't seem to happen in 
practice.  Since xl has not been able to generate those xenstore events 
prior to the `xl suspend` introduction, this code path hasn't run or 
been an issue.
The tag would be:
Fixes: 1a0e17891f ("xl: support on_{poweroff,reboot,crash} domain 
configuration options.")
Regards,
Jason