On Mon, 2016-09-05 at 13:16 +1000, Balbir Singh wrote: .../... > > Cc: Peter Zijlstra <[email protected]> > Cc: Nicholas Piggin <[email protected]>
Acked-by: Benjamin Herrenschmidt <[email protected]> > Signed-off-by: Balbir Singh <[email protected]> > --- > 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; >
