On Mon, Feb 03, 2014 at 10:19:29AM +0400, Cyrill Gorcunov wrote: > On Wed, Jan 29, 2014 at 03:17:17PM -0500, Don Zickus wrote: > > > > I am not entirely sure on the corruption path, but what happens is: > > > > > > > > o perf schedules a group with p4_pmu_schedule_events() > > > > o inside p4_pmu_schedule_events(), it notices an hwc pointer is being > > > > reused > > > > but for a different cpu, so it 'swaps' the config bits and returns the > > > > updated 'assign' array with a _new_ index. > > > > o perf schedules another group with p4_pmu_schedule_events() > > > > o inside p4_pmu_schedule_events(), it notices an hwc pointer is being > > > > reused > > > > (the same one as above) but for the _same_ cpu [BUG!!], so it updates > > > > the > > > > 'assign' array to use the _old_ (wrong cpu) index because the _new_ > > > > index is in > > > > an earlier part of the 'assign' array (and hasn't been committed yet). > > > > o perf commits the transaction using the wrong index and corrupts the > > > > other cpu > > > > > > Thanks for the fix Don! I fear I won't be able to look precisely tonight, > > > so > > > could it wait until tomorrow? (If it's critical sure such fix should do > > > the > > > trick). > > > > There is no rush. Early next week is fine too. :-) > > Hi Don, sorry for delay. I thought maybe extending match_prev_assignment() > would be better (ie to figure out if previous event can run without > reprogramming the counter) but this makes code only harder (and what > is worse -- having no physical accees to p4 machine leaves no chance > to test changes). So eventually I think your patch does the same thing > as I had in mind but in different way. Thus > > Acked-by: Cyrill Gorcunov <gorcu...@openvz.org> > > thanks a lot!
thanks! Cheers, Don -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
