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Message-ID: <20151007123852.GH17308@twins.programming.kicks-ass.net> Date: Wed, 7 Oct 2015 14:38:52 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Oleg Nesterov <oleg@...hat.com> 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 Wed, Oct 07, 2015 at 02:30:46PM +0200, Oleg Nesterov wrote: > 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. Yes, I was looking at that, this issue reminded me we still had that issue open. > 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 ;) Sure, take your time. -- 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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