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authorSebastian Andrzej Siewior <bigeasy@linutronix.de>2017-01-24 15:40:06 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-03-31 09:49:54 +0200
commit2bed5987692cb6dc3bf3ce15d8abeb79fdf4ab2a (patch)
parent7a5202190810dde1467718235c1f650fcf57592a (diff)
sched/rt: Add a missing rescheduling point
commit 619bd4a71874a8fd78eb6ccf9f272c5e98bcc7b7 upstream. Since the change in commit: fd7a4bed1835 ("sched, rt: Convert switched_{from, to}_rt() / prio_changed_rt() to balance callbacks") ... we don't reschedule a task under certain circumstances: Lets say task-A, SCHED_OTHER, is running on CPU0 (and it may run only on CPU0) and holds a PI lock. This task is removed from the CPU because it used up its time slice and another SCHED_OTHER task is running. Task-B on CPU1 runs at RT priority and asks for the lock owned by task-A. This results in a priority boost for task-A. Task-B goes to sleep until the lock has been made available. Task-A is already runnable (but not active), so it receives no wake up. The reality now is that task-A gets on the CPU once the scheduler decides to remove the current task despite the fact that a high priority task is enqueued and waiting. This may take a long time. The desired behaviour is that CPU0 immediately reschedules after the priority boost which made task-A the task with the lowest priority. Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Thomas Gleixner <tglx@linutronix.de> Fixes: fd7a4bed1835 ("sched, rt: Convert switched_{from, to}_rt() prio_changed_rt() to balance callbacks") Link: http://lkml.kernel.org/r/20170124144006.29821-1-bigeasy@linutronix.de Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2 files changed, 2 insertions, 4 deletions
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 8b0a15e285f9..e984f059e5fc 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1771,12 +1771,11 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p)
if (p->nr_cpus_allowed > 1 && rq->dl.overloaded)
if (dl_task(rq->curr))
check_preempt_curr_dl(rq, p, 0);
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 8ec86abe0ea1..78ae5c1d9412 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2136,10 +2136,9 @@ static void switched_to_rt(struct rq *rq, struct task_struct *p)
if (p->nr_cpus_allowed > 1 && rq->rt.overloaded)
+#endif /* CONFIG_SMP */
if (p->prio < rq->curr->prio)
-#endif /* CONFIG_SMP */