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Message-ID: <20151007123046.GA21460@redhat.com> Date: Wed, 7 Oct 2015 14:30:46 +0200 From: Oleg Nesterov <oleg@...hat.com> To: Peter Zijlstra <peterz@...radead.org> Cc: heiko.carstens@...ibm.com, linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>, Ingo Molnar <mingo@...nel.org>, Rik van Riel <riel@...hat.com> Subject: Re: [RFC][PATCH] sched: Start stopper early On 10/07, Peter Zijlstra wrote: > > So Heiko reported some 'interesting' fail where stop_two_cpus() got > stuck in multi_cpu_stop() with one cpu waiting for another that never > happens. > > It _looks_ like the 'other' cpu isn't running and the current best > theory is that we race on cpu-up and get the stop_two_cpus() call in > before the stopper task is running. > > This _is_ possible because we set 'online && active' Argh. Can't really comment this change right now, but this reminds me that stop_two_cpus() path should not rely on cpu_active() at all. I mean we should not use this check to avoid the deadlock, migrate_swap_stop() can check it itself. And cpu_stop_park()->cpu_stop_signal_done() should be replaced by BUG_ON(). Probably slightly off-topic, but what do you finally think about the old "[PATCH v2 6/6] stop_machine: kill stop_cpus_lock and lg_double_lock/unlock()" we discussed in http://marc.info/?t=143750670300014 ? I won't really insist if you still dislike it, but it seems we both agree that "lg_lock stop_cpus_lock" must die in any case, and after that we can the cleanups mentioned above. And, Peter, I see a lot of interesting emails from you, but currently can't even read them. I hope very much I will read them later and perhaps even reply ;) Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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