sched: Fix ->min_vruntime calculation in dequeue_entity()

Dima Zavin <dima@android.com> reported:

"After pulling the thread off the run-queue during a cgroup change,
the cfs_rq.min_vruntime gets recalculated. The dequeued thread's vruntime
then gets normalized to this new value. This can then lead to the thread
getting an unfair boost in the new group if the vruntime of the next
task in the old run-queue was way further ahead."

Reported-by: Dima Zavin <dima@android.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Recalls-having-tested-once-upon-a-time-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1305674470-23727-1-git-send-email-john.stultz@linaro.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index e32a9b70ee9c716149d57a33f298495d368b292c..433491c2dc8f5c9952655de72958c7019dadd57f 100644 (file)
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1076,8 +1076,6 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
        se->on_rq = 0;
        update_cfs_load(cfs_rq, 0);
        account_entity_dequeue(cfs_rq, se);
-       update_min_vruntime(cfs_rq);
-       update_cfs_shares(cfs_rq);
 
        /*
         * Normalize the entity after updating the min_vruntime because the
@@ -1086,6 +1084,9 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
         */
        if (!(flags & DEQUEUE_SLEEP))
                se->vruntime -= cfs_rq->min_vruntime;
+
+       update_min_vruntime(cfs_rq);
+       update_cfs_shares(cfs_rq);
 }
 
 /*