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SubjectRe: [PATCH 1/1] hotplug cpu: migrate a task within its cpuset

* Nathan Lynch <ntl@pobox.com> wrote:

> > > + /* try to stay on the same cpuset */
> > > + if (dest_cpu == NR_CPUS) {
> > > + p->cpus_allowed = cpuset_cpus_allowed(p);
> > > + dest_cpu = any_online_cpu(p->cpus_allowed);
> > > + }
> >
> > what's the practical effect of this - when moving the last CPU offline
> > from a node you got jobs migrated to really alien nodes? Thus i think we
> > should queue this up for v2.6.21 too, correct? It's a NOP on systems
> > that do not set up cpusets, so it's low-risk.
>
> See my earlier reply to this patch. Calling cpuset_cpus_allowed
> (which takes a mutex) here is a bug, since move_task_off_dead_cpu must
> be called with interrupts disabled.

ouch. i only checked the !CONFIG_CPUSET case :-/ It's a really bad idea
to have any locking there indeed. The name itself suggests some atomic
action.

Ingo
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