On Tue, Feb 17, 2015 at 01:12:58PM +0100, Peter Zijlstra wrote: > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -341,6 +341,22 @@ static struct rq *task_rq_lock(struct ta > 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);
Hey Paul, remember this: https://lkml.org/lkml/2014/7/16/310 I just used a creative one :-) BTW, should we attempt to include that table in memory-barriers.txt like Mathieu said? As a cheat sheet with references to longer explanations for the 'interesting' ones? FWIW, we should probably update that table to include control dependencies too; we didn't (formally) have those back then I think. The blob under SMP BARRIER PAIRING does not mention pairing with control dependencies; and I'm rather sure I've done so. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
