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

[Ingo Molnar <mingo@elte.hu>]

* 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