On 09/10, Boqun Feng wrote: > > On Wed, Sep 09, 2015 at 12:28:22PM -0700, Paul E. McKenney wrote: > > My feeling is > > that we should avoid saying too much about the internals of wait_event() > > and wake_up(). I feel the same. I simply can't understand what we are trying to document ;) For example, > A STORE-LOAD barrier is implied after setting task state by wait-related functions: > > prepare_to_wait(); > prepare_to_wait_exclusive(); > prepare_to_wait_event(); I won't argue, but to me this looks misleading too. Yes, prepare_to_wait()->set_current_state() implies mb() and thus a STORE-LOAD barrier. But this has nothing to do with the explanation above. We do not need this barrier to avoid the race with wake_up(). Again, again, we can safely rely on wq->lock and acquire/release semantics. This barrier is only needed if you do, say, CONDITION = 1; if (waitqueue_active(wq)) wake_up(wq); And note that the code above is wrong without another mb() after CONDITION = 1. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
