Re: [PATCH] xen: postpone updating domains' node affinity when removing a CPU from a cpupool

[Dario Faggioli <dario.faggioli@citrix.com>]

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On Mon, 2015-03-09 at 17:49 +0100, Dario Faggioli wrote:
> 93be8285 ("update domU's node-affinity on the cpupool_unassign_cpu()
> path")  does the right thing, but does it too early. In fact, it
> is necessary to call domain_update_node_affinity() when a pCPU is
> removed from a cpupool, but that must happen after the pCPU is
> really gone from there.
> 
> More specifically, it is important that the update happens not
> before cpu_disable_scheduler() is called on that pCPU, to give
> that function the chance to fixup the vCPU affinity of the
> domains residing in the cpupool, if that is necessary.
> 
> Calling it earlier, as it happens before this change, causes
> (although only in rather awkward circumstances), the following:
> 
> (XEN) ****************************************
> (XEN) Panic on CPU 0:
> (XEN) Assertion '!cpumask_empty(dom_cpumask)' failed at domain.c:460
> (XEN) ****************************************
> 
Oh, and this affects 4.5, so, when we'll get there, a backport is in
order, IMO (and I'll file the request as appropriate as soon as this
will be in).

Regards,
Dario

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