On 17/07/2015 04:25, Fam Zheng wrote: > What if aio_notify happens after the previous aio_dispatch() but before the > next necessary atomic_add? The aio_notify would still skip the > event_notifier_set(), and the next ppoll() will not return. For example: > > Thread A Thread B > ------------------------------------------------------------------------ > aio_poll(blocking=true) > aio_notify() > smp_mb() > if (ctx->notify_me) /* false! */ > atomic_add(ctx->notify_me, 2) > ppoll() > atomic_sub(ctx->notify_me, 2) event_notifier_set() /* not run */
It's not a problem because ppoll() has exited. The next call to aio_poll or aio_ctx_prepare will notice the bottom half, do a non-blocking ppoll(), and then service the bottom half. > > And if that's not a problem, why don't we need something like ACCESS_ONCE in > aio_noitfy()? Because there's already a smp_mb() which is stronger. Paolo
