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sched/deadline: Add more reschedule cases to prio_changed_dl()

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I've been tracking down an issue on a ~5.17ish kernel where:

  CPUx                           CPUy

  <DL task p0 owns an rtmutex M>
  <p0 depletes its runtime, gets throttled>
  <rq switches to the idle task>
				 <DL task p1 blocks on M, boost/replenish p0>
				 <No call to resched_curr() happens here>

  [idle task keeps running here until *something*
   accidentally sets TIF_NEED_RESCHED]

On that kernel, it is quite easy to trigger using rt-tests's deadline_test
[1] with the test running on isolated CPUs (this reduces the chance of
something unrelated setting TIF_NEED_RESCHED on the idle tasks, making the
issue even more obvious as the hung task detector chimes in).

I haven't been able to reproduce this using a mainline kernel, even if I
revert

  2972e3050e ("tracing: Make trace_marker{,_raw} stream-like")

which gets rid of the lock involved in the above test, *but* I cannot
convince myself the issue isn't there from looking at the code.

Make prio_changed_dl() issue a reschedule if the current task isn't a
deadline one. While at it, ensure a reschedule is emitted when a
queued-but-not-current task gets boosted with an earlier deadline that
current's.

[1]: https://git.kernel.org/pub/scm/utils/rt-tests/rt-tests.git

Signed-off-by: Valentin Schneider <vschneid@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lore.kernel.org/r/20230206140612.701871-1-vschneid@redhat.com
This commit is contained in:
Valentin Schneider 2023-02-06 14:06:12 +00:00 committed by Peter Zijlstra
parent 829c1651e9
commit 7ea98dfa44
1 changed files with 28 additions and 16 deletions
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44
kernel/sched/deadline.c
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@ -2663,17 +2663,20 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p)
static void prio_changed_dl(struct rq *rq, struct task_struct *p,
int oldprio)
{
if (task_on_rq_queued(p) || task_current(rq, p)) {
#ifdef CONFIG_SMP
/*
* This might be too much, but unfortunately
* we don't have the old deadline value, and
* we can't argue if the task is increasing
* or lowering its prio, so...
*/
if (!rq->dl.overloaded)
deadline_queue_pull_task(rq);
if (!task_on_rq_queued(p))
return;
#ifdef CONFIG_SMP
/*
* This might be too much, but unfortunately
* we don't have the old deadline value, and
* we can't argue if the task is increasing
* or lowering its prio, so...
*/
if (!rq->dl.overloaded)
deadline_queue_pull_task(rq);
if (task_current(rq, p)) {
/*
* If we now have a earlier deadline task than p,
* then reschedule, provided p is still on this
@ -2681,15 +2684,24 @@ static void prio_changed_dl(struct rq *rq, struct task_struct *p,
*/
if (dl_time_before(rq->dl.earliest_dl.curr, p->dl.deadline))
resched_curr(rq);
#else
} else {
/*
* Again, we don't know if p has a earlier
* or later deadline, so let's blindly set a
* (maybe not needed) rescheduling point.
* Current may not be deadline in case p was throttled but we
* have just replenished it (e.g. rt_mutex_setprio()).
*
* Otherwise, if p was given an earlier deadline, reschedule.
*/
resched_curr(rq);
#endif /* CONFIG_SMP */
if (!dl_task(rq->curr) ||
dl_time_before(p->dl.deadline, rq->curr->dl.deadline))
resched_curr(rq);
}
#else
/*
* We don't know if p has a earlier or later deadline, so let's blindly
* set a (maybe not needed) rescheduling point.
*/
resched_curr(rq);
#endif
}
DEFINE_SCHED_CLASS(dl) = {