diff options
Diffstat (limited to 'fs/eventpoll.c')
| -rw-r--r-- | fs/eventpoll.c | 22 |
1 files changed, 21 insertions, 1 deletions
diff --git a/fs/eventpoll.c b/fs/eventpoll.c index c0b3c70ee87a..33c9599c14e7 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -1226,11 +1226,31 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_even * otherwise we might miss an event that happens between the * f_op->poll() call and the new event set registering. */ - epi->event.events = event->events; + epi->event.events = event->events; /* need barrier below */ pt._key = event->events; epi->event.data = event->data; /* protected by mtx */ /* + * The following barrier has two effects: + * + * 1) Flush epi changes above to other CPUs. This ensures + * we do not miss events from ep_poll_callback if an + * event occurs immediately after we call f_op->poll(). + * We need this because we did not take ep->lock while + * changing epi above (but ep_poll_callback does take + * ep->lock). + * + * 2) We also need to ensure we do not miss _past_ events + * when calling f_op->poll(). This barrier also + * pairs with the barrier in wq_has_sleeper (see + * comments for wq_has_sleeper). + * + * This barrier will now guarantee ep_poll_callback or f_op->poll + * (or both) will notice the readiness of an item. + */ + smp_mb(); + + /* * Get current event bits. We can safely use the file* here because * its usage count has been increased by the caller of this function. */ |