Messages in this thread | | | Subject | Re: [RESEND][v2][PATCH] Fix a race between try_to_wake_up() and a woken up task | From | Benjamin Herrenschmidt <> | Date | Mon, 05 Sep 2016 17:14:19 +1000 |
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On Mon, 2016-09-05 at 13:16 +1000, Balbir Singh wrote:
.../... > > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Nicholas Piggin <npiggin@gmail.com>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Signed-off-by: Balbir Singh <bsingharora@gmail.com> > --- > kernel/sched/core.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 2a906f2..582c684 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -2016,6 +2016,17 @@ try_to_wake_up(struct task_struct *p, unsigned > int state, int wake_flags) > success = 1; /* we're going to change ->state */ > cpu = task_cpu(p); > > + /* > + * Ensure we see on_rq and p_state consistently > + * > + * For example in __rwsem_down_write_failed(), we have > + * [S] ->on_rq = 1 [L] > ->state > + * MB RMB > + * [S] ->state = TASK_UNINTERRUPTIBLE [L] ->on_rq > + * In the absence of the RMB p->on_rq can be observed to be > 0 > + * and we end up spinning indefinitely in while (p->on_cpu) > + */ > + smp_rmb(); > if (p->on_rq && ttwu_remote(p, wake_flags)) > goto stat; >
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