On Mon, Sep 5, 2016 at 5:48 PM, Peter Zijlstra <[email protected]> wrote: > On Mon, Sep 05, 2016 at 05:14:19PM +1000, Benjamin Herrenschmidt wrote: >> 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) >> > + */ > > So I did replace that comment with the one I proposed earlier. I checked > a fair number of architectures and many did not have an obvious barrier > in switch_to(). So that is not something we can rely on, nor do we need > to I think. >
Thanks for the comment edit and thanks for letting us know. Balbir Singh
