Messages in this thread | | | Subject | Re: [PATCH v8 -tip 02/26] sched: Introduce sched_class::pick_task() | From | "Li, Aubrey" <> | Date | Sun, 25 Oct 2020 07:48:15 +0800 |
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On 2020/10/24 20:27, Vineeth Pillai wrote: > > > On 10/24/20 7:10 AM, Vineeth Pillai wrote: >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index 93a3b874077d..4cae5ac48b60 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -4428,12 +4428,14 @@ pick_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *curr) >> se = second; >> } >> >> - if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1) { >> + if (left && cfs_rq->next && >> + wakeup_preempt_entity(cfs_rq->next, left) < 1) { >> /* >> * Someone really wants this to run. If it's not unfair, run it. >> */ >> se = cfs_rq->next; >> - } else if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, left) < 1) { >> + } else if (left && cfs_rq->last && >> + wakeup_preempt_entity(cfs_rq->last, left) < 1) { >> /* >> * Prefer last buddy, try to return the CPU to a preempted task. >> >> >> There reason for left being NULL needs to be investigated. This was >> there from v1 and we did not yet get to it. I shall try to debug later >> this week. > > Thinking more about it and looking at the crash, I think that > 'left == NULL' can happen in pick_next_entity for core scheduling. > If a cfs_rq has only one task that is running, then it will be > dequeued and 'left = __pick_first_entity()' will be NULL as the > cfs_rq will be empty. This would not happen outside of coresched > because we never call pick_tack() before put_prev_task() which > will enqueue the task back. > > With core scheduling, a cpu can call pick_task() for its sibling while > the sibling is still running the active task and put_prev_task has yet > not been called. This can result in 'left == NULL'. So I think the > above fix is appropriate when core scheduling is active. It could be > cleaned up a bit though.
This patch works, thanks Vineeth for the quick fix!
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