Re: [Xen-devel] [PATCH] xen/sched: fix get_cpu_idle_time() with core scheduling

[Dario Faggioli <dfaggioli@xxxxxxxx>]

On Thu, 2020-02-13 at 15:35 +0100, Juergen Gross wrote:
> get_cpu_idle_time() is calling vcpu_runstate_get() for an idle vcpu.
> With core scheduling active this is fragile, as idle vcpus are
> assigned
> to other scheduling units temporarily, and that assignment is changed
> in some cases without holding the scheduling lock, and
> vcpu_runstate_get() is using v->sched_unit as parameter for
> unit_schedule_[un]lock_irq(), resulting in an ASSERT() triggering in
> unlock in case v->sched_unit has changed meanwhile.
> 
> Fix that by using a local unit variable holding the correct unit.
> 
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
>
Reviewed-by: Dario Faggioli <dfaggioli@xxxxxxxx>

And...

> I have verified that all other uses of v->sched_unit are not
> problematic: they are all for non-idle vcpus, or in scheduling paths
> dealing with scheduling themselves and thus being aware of the
> potential problem or not vulnerable by it.
>
... Thanks for having done this as well. :-)

Regards
-- 
Dario Faggioli, Ph.D
http://about.me/dario.faggioli
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
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