From: Dario Faggioli <dfaggioli@suse.com>
To: "julien@xen.org" <julien@xen.org>,
"ahmeddan@amazon.co.uk" <ahmeddan@amazon.co.uk>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: "sstabellini@kernel.org" <sstabellini@kernel.org>,
"mpohlack@amazon.de" <mpohlack@amazon.de>,
"jgrall@amazon.co.uk" <jgrall@amazon.co.uk>,
"doebel@amazon.de" <doebel@amazon.de>
Subject: Re: NULL scheduler DoS
Date: Wed, 11 Aug 2021 10:09:25 +0000 [thread overview]
Message-ID: <6b5e28f427ccd89505a4448f2b9e5be992a08292.camel@suse.com> (raw)
In-Reply-To: <f3082b8c-1388-c92b-6175-e6d8b9d4cab4@xen.org>
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On Mon, 2021-08-09 at 21:38 +0100, Julien Grall wrote:
> On 09/08/2021 18:35, Julien Grall wrote:
> >
> > This implies that a pCPU may temporarily be assigned to two vCPUs
> > and we
> > expect to be fixed up afterwards. However, a domain may be
> > destroyed
> > before this is happening.
> >
> > So it looks like that unit_deassign() is not able to cope with this
> > case. From a brief look, I think we may want to check if the pCPU
> > is in
> > the wait list. If it is, then we should bail out.
>
> Actually, I was wrong. It looks like null_unit_remove() is already
> checking this condition. Also, the vCPU should be offline (and the
> unit
> as well) because they haven't come online yet:
>
That's what is currently puzzling me.
I mean, the crash happens in unit_deassign(), called by
null_unit_remove(), called by sched_destroy_vcpu().
And I agree that the unit should be offline, but null_unit_remove()
calls unit_deassign() only if the unit *is* online, so... What's going
on? :-/
Regards
--
Dario Faggioli, Ph.D
http://about.me/dario.faggioli
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
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next prev parent reply other threads:[~2021-08-11 10:09 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-09 16:19 NULL scheduler DoS Ahmed, Daniele
2021-08-09 16:47 ` Ahmed, Daniele
2021-08-09 17:35 ` Julien Grall
2021-08-09 20:38 ` Julien Grall
2021-08-11 10:09 ` Dario Faggioli [this message]
2021-09-08 8:01 ` Ahmed, Daniele
2021-12-17 15:03 ` Ahmed, Daniele
2021-08-11 9:59 ` Dario Faggioli
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