smp_call_function_many SMP race
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From: Peter Zijlstra on 23 Mar 2010 08:30 On Tue, 2010-03-23 at 22:15 +1100, Anton Blanchard wrote: > > It turns out commit c0f68c2fab4898bcc4671a8fb941f428856b4ad5 (generic-ipi: > cleanup for generic_smp_call_function_interrupt()) is at fault. It removes > locking from smp_call_function_many and in doing so creates a rather > complicated race. A rather simple question since my brain isn't quite ready processing the content here.. Isn't reverting that one patch a simpler solution than adding all that extra logic? If not, then the above statement seems false and we had a bug even with that preempt_enable/disable() pair. Just wondering.. :-) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Paul E. McKenney on 23 Mar 2010 11:40 On Tue, Mar 23, 2010 at 01:26:43PM +0100, Peter Zijlstra wrote: > On Tue, 2010-03-23 at 22:15 +1100, Anton Blanchard wrote: > > > > It turns out commit c0f68c2fab4898bcc4671a8fb941f428856b4ad5 (generic-ipi: > > cleanup for generic_smp_call_function_interrupt()) is at fault. It removes > > locking from smp_call_function_many and in doing so creates a rather > > complicated race. > > A rather simple question since my brain isn't quite ready processing the > content here.. > > Isn't reverting that one patch a simpler solution than adding all that > extra logic? If not, then the above statement seems false and we had a > bug even with that preempt_enable/disable() pair. > > Just wondering.. :-) If I understand correctly, if you want to fix it by reverting patches, you have to revert back to simple locking (up to and including 54fdade1c3332391948ec43530c02c4794a38172). And I believe that the poor performance of simple locking was whole reason for the series of patches. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Peter Zijlstra on 23 Mar 2010 12:00 On Tue, 2010-03-23 at 08:33 -0700, Paul E. McKenney wrote: > On Tue, Mar 23, 2010 at 01:26:43PM +0100, Peter Zijlstra wrote: > > On Tue, 2010-03-23 at 22:15 +1100, Anton Blanchard wrote: > > > > > > It turns out commit c0f68c2fab4898bcc4671a8fb941f428856b4ad5 (generic-ipi: > > > cleanup for generic_smp_call_function_interrupt()) is at fault. It removes > > > locking from smp_call_function_many and in doing so creates a rather > > > complicated race. > > > > A rather simple question since my brain isn't quite ready processing the > > content here.. > > > > Isn't reverting that one patch a simpler solution than adding all that > > extra logic? If not, then the above statement seems false and we had a > > bug even with that preempt_enable/disable() pair. > > > > Just wondering.. :-) > > If I understand correctly, if you want to fix it by reverting patches, > you have to revert back to simple locking (up to and including > 54fdade1c3332391948ec43530c02c4794a38172). And I believe that the poor > performance of simple locking was whole reason for the series of patches. Right, then c0f68c2 did not in fact cause this bug.. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Anton Blanchard on 23 Mar 2010 17:40
Hi Peter, > A rather simple question since my brain isn't quite ready processing the > content here.. After working my way through that bug my brain wasn't in good shape either because: > Isn't reverting that one patch a simpler solution than adding all that > extra logic? If not, then the above statement seems false and we had a > bug even with that preempt_enable/disable() pair. I screwed up the explanation :( The commit message that causes it is 54fdade1c3332391948ec43530c02c4794a38172 (generic-ipi: make struct call_function_data lockless), and backing it out fixes the issue. Anton -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |