On 10/10/2013 02:17 PM, 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>
Reviewed-by: Rik van Riel <riel@xxxxxxxxxx> -- 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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