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Re: [PATCH for-4.17?] x86/paging: return -EINVAL for paging domctls for dying domains
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Wed, 9 Nov 2022 12:36:38 +0100
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- Cc: Henry.Wang@xxxxxxx, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Edwin Török <edvin.torok@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Wed, 09 Nov 2022 11:37:02 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Wed, Nov 09, 2022 at 11:23:01AM +0100, Jan Beulich wrote:
> On 09.11.2022 11:11, Roger Pau Monné wrote:
> > On Wed, Nov 09, 2022 at 08:48:46AM +0100, Jan Beulich wrote:
> >> Finally I'm not convinced of the usefulness of this dying check in the
> >> first place: is_dying may become set immediately after the check was
> >> done.
> >
> > While strictly true, this code is executed with the domain lock held,
> > so while is_dying might change, domain_kill() won't make progress
> > because of the barrier on the domain lock just after setting is_dying.
>
> I guess I'm confused now: This code is called with the domctl lock
> held, which - as said before - is a questionable thing, for serializing
> things more than necessary as well as for holding this lock for
> excessive periods of time. IOW I consider it wrong to depend on that
> in paging_domctl() to synchronize against domain_kill(). Yet indeed that
> should eliminate races at present.
Right, both are domctls. There are other places where is_dying get
set as part of failures in the domain create paths, but then the
paging domctl failing would be natural, as the domain is being
destroyed as part of a failed domain create.
Since I don't see replies to my other comments, do you agree on
returning an error then?
Thanks, Roger.
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