Commit 7355690e authored by Ingo Molnar's avatar Ingo Molnar Committed by Linus Torvalds

[PATCH] sched: fix SMT scheduler bug

The SMT scheduler incorrectly skips kernel threads even if they are
runnable (but they are preempted by a higher-prio user-space task which got
SMT-delayed by an even higher-priority task running on a sibling CPU).

Fix this for now by only doing the SMT-nice optimization if the
to-be-delayed task is the only runnable task.  (This should cover most of
the real-life cases anyway.)

This bug has been in the SMT scheduler since 2.6.17 or so, but has only
been noticed now by the active check in the dynticks code.
Signed-off-by: default avatarIngo Molnar <>
Cc: Michal Piotrowski <>
Cc: Nick Piggin <>
Cc: Thomas Gleixner <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 3f555c70
......@@ -3547,7 +3547,7 @@ asmlinkage void __sched schedule(void)
next->sleep_type = SLEEP_NORMAL;
if (dependent_sleeper(cpu, rq, next))
if (rq->nr_running == 1 && dependent_sleeper(cpu, rq, next))
next = rq->idle;
if (next == rq->idle)
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