On Thu, Oct 10, 2013 at 08:17:22PM +0200, Peter Zijlstra wrote: > On Wed, Oct 09, 2013 at 10:30:13AM -0700, tip-bot for Peter Zijlstra wrote: > > sched/numa: Introduce migrate_swap() > > Thanks to Rik for writing the Changelog! > > --- > From: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > Subject: sched: Fix race in migrate_swap_stop > > There is a subtle race in migrate_swap, when task P, on CPU A, decides to swap > places with task T, on CPU B. > > Task P: > - call migrate_swap > Task T: > - go to sleep, removing itself from the runqueue > Task P: > - double lock the runqueues on CPU A & B > Task T: > - get woken up, place itself on the runqueue of CPU C > Task P: > - see that task T is on a runqueue, and pretend to remove it > from the runqueue on CPU B > > Now CPUs B & C both have corrupted scheduler data structures. > > This patch fixes it, by holding the pi_lock for both of the tasks > involved in the migrate swap. This prevents task T from waking up, > and placing itself onto another runqueue, until after migrate_swap > has released all locks. > > This means that, when migrate_swap checks, task T will be either > on the runqueue where it was originally seen, or not on any > runqueue at all. Migrate_swap deals correctly with of those cases. > > Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > Tested-by: Joe Mario <jmario@xxxxxxxxxx> Acked-by: Mel Gorman <mgorman@xxxxxxx> -- Mel Gorman SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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