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Re: [PATCH for-4.17?] x86/paging: return -EINVAL for paging domctls for dying domains
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 9 Nov 2022 11:23:01 +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 10:23:16 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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.
Jan
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