Commit-ID: 74b8a4cb6ce3685049ee124243a52238c5cabe55 Gitweb: http://git.kernel.org/tip/74b8a4cb6ce3685049ee124243a52238c5cabe55 Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx> AuthorDate: Tue, 17 Feb 2015 13:07:38 +0100 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitDate: Wed, 18 Feb 2015 14:27:28 +0100 sched: Clarify ordering between task_rq_lock() and move_queued_task() There was a wee bit of confusion around the exact ordering here; clarify things. Reported-by: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Oleg Nesterov <oleg@xxxxxxxxxx> Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> Link: http://lkml.kernel.org/r/20150217121258.GM5029@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> --- kernel/sched/core.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 1f37fe7..fd0a6ed 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -341,6 +341,22 @@ static struct rq *task_rq_lock(struct task_struct *p, unsigned long *flags) raw_spin_lock_irqsave(&p->pi_lock, *flags); rq = task_rq(p); raw_spin_lock(&rq->lock); + /* + * move_queued_task() task_rq_lock() + * + * ACQUIRE (rq->lock) + * [S] ->on_rq = MIGRATING [L] rq = task_rq() + * WMB (__set_task_cpu()) ACQUIRE (rq->lock); + * [S] ->cpu = new_cpu [L] task_rq() + * [L] ->on_rq + * RELEASE (rq->lock) + * + * If we observe the old cpu in task_rq_lock, the acquire of + * the old rq->lock will fully serialize against the stores. + * + * If we observe the new cpu in task_rq_lock, the acquire will + * pair with the WMB to ensure we must then also see migrating. + */ if (likely(rq == task_rq(p) && !task_on_rq_migrating(p))) return rq; raw_spin_unlock(&rq->lock); -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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