Re: [lhcs-devel] Re: CPU Hotplug broken -mm5 onwards

From: Rusty Russell
Date: Mon Apr 19 2004 - 18:10:17 EST

On Tue, 2004-04-20 at 08:55, Nick Piggin wrote:
> > So, as Rusty said, I think we really need to consider removing
> > lock_cpu_hotplug from sched_migrate_task. AFAICS that lock
> > was needed to prevent adding tasks to dead cpus. The same
> > can be accomplished by removing lock_cpu_hotplug from sched_migrate_task
> > and adding a cpu_is_offline check in __migrate_task.
> > This will eliminate all the deadlocks I have been hitting.
> >
> Yes this would be a better idea. Care to send Andrew a patch
> against -mm?

What surprises me is that this is a regression. The original hotplug
code on top of Nicksched(TM) removed that lock as part of the "don't
change cpus_allowed to migrate on exec" fix. When we pushed the patch
straight into Linus' tree, we had to do lock_cpu_hotplug because we
didn't have that code.

Obviously, it escaped somewhere...

Anyone who quotes me in their signature is an idiot -- Rusty Russell

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