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authorPeter Zijlstra <peterz@infradead.org>2013-10-10 20:17:22 +0200
committerIngo Molnar <mingo@kernel.org>2013-10-16 14:22:14 +0200
commit746023159c40c523b08a3bc3d213dac212385895 (patch)
tree5ec30b81b256a202bf44940360dd1849325c4af8 /kernel/stop_machine.c
parent7c3f2ab7b844f1a859afbc3d41925e8a0faba5fa (diff)
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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. Tested-by: Joe Mario <jmario@redhat.com> Acked-by: Mel Gorman <mgorman@suse.de> Reviewed-by: Rik van Riel <riel@redhat.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: hannes@cmpxchg.org Cc: aarcange@redhat.com Cc: srikar@linux.vnet.ibm.com Cc: tglx@linutronix.de Cc: hpa@zytor.com Link: http://lkml.kernel.org/r/20131010181722.GO13848@laptop.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/stop_machine.c')
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