Messages in this thread | | | Date | Wed, 14 May 2014 13:20:48 +0200 | From | Peter Zijlstra <> | Subject | Re: sched: hang in migrate_swap |
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On Wed, May 14, 2014 at 12:26:02PM +0200, Peter Zijlstra wrote: > so we serialize stop_cpus_work() vs stop_two_cpus() with an l/g lock. > > Ah, but stop_cpus_work() only holds the global lock over queueing, it > doesn't wait for completion, that might indeed cause a problem.
Hmm, is this so? If the stop_cpus_work() queueing is complete, the stop_two_cpus() queueing must always happen _after_ it.
Therefore the stopper threads should also observe them in that order, right? /me goes check..
Hmm, cpu_stop_queue_work() does list_add_tail(), does that make it a LIFO?
Bah, now I've confused myself again.
> Also, since its two different cpus queueing, the ordered queue doesn't > really matter, you can still interleave the all and two sets and get > into this state.
Anyway, before I stared getting self doubts, I wrote the below, now I'm not sure its at all relevant but here goes.
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Yeah, sorry for not also providing a solution, extending the lg_global lock over the entire sqeuence won't work for it will disable preemption, which means we need something a little smarter.
Now, I still have the hotplug lock rewrite laying about, now Linus had an opinion on that, but we could adapt percpu-rwsem.c to use the same logic.
At that point, I think it would be possible to use the percpu-rwsem for this, use the write lock for the global stop all thing, and the read side for the two-cpu stopper.
http://thread.gmane.org/gmane.linux.kernel/1574737
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