Messages in this thread Patch in this message | | | Date | Tue, 24 Feb 2009 12:27:43 -0500 | From | Tony Battersby <> | Subject | [PATCH 5/6] [2.6.29] epoll: clean up ep_modify |
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ep_modify() doesn't need to set event.data from within the ep->lock spinlock as the comment suggests. The only place event.data is used is ep_send_events(), and this is protected by ep->mtx instead of ep->lock. Also update the comment for mutex_lock() at the top of ep_send_events(), which mentions epoll_ctl(EPOLL_CTL_DEL) but not epoll_ctl(EPOLL_CTL_MOD).
ep_modify() can also use spin_lock_irq() instead of spin_lock_irqsave().
Signed-off-by: Tony Battersby <tonyb@cybernetics.com> ---
This patch is against 2.6.29-rc6; however, it doesn't need to go into 2.6.29. Use the -mm version instead if applying after the other patches in -mm.
--- a/fs/eventpoll.c 2009-02-23 15:37:14.000000000 -0500 +++ b/fs/eventpoll.c 2009-02-23 15:38:04.000000000 -0500 @@ -885,15 +885,14 @@ static int ep_modify(struct eventpoll *e { int pwake = 0; unsigned int revents; - unsigned long flags; /* - * Set the new event interest mask before calling f_op->poll(), otherwise - * a potential race might occur. In fact if we do this operation inside - * the lock, an event might happen between the f_op->poll() call and the - * new event set registering. + * Set the new event interest mask before calling f_op->poll(); + * 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.data = event->data; /* protected by mtx */ /* * Get current event bits. We can safely use the file* here because @@ -901,16 +900,12 @@ static int ep_modify(struct eventpoll *e */ revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL); - spin_lock_irqsave(&ep->lock, flags); - - /* Copy the data member from inside the lock */ - epi->event.data = event->data; - /* * If the item is "hot" and it is not registered inside the ready * list, push it inside. */ if (revents & event->events) { + spin_lock_irq(&ep->lock); if (!ep_is_linked(&epi->rdllink)) { list_add_tail(&epi->rdllink, &ep->rdllist); @@ -920,8 +915,8 @@ static int ep_modify(struct eventpoll *e if (waitqueue_active(&ep->poll_wait)) pwake++; } + spin_unlock_irq(&ep->lock); } - spin_unlock_irqrestore(&ep->lock, flags); /* We have to call this outside the lock */ if (pwake) @@ -943,7 +938,7 @@ static int ep_send_events(struct eventpo /* * We need to lock this because we could be hit by - * eventpoll_release_file() and epoll_ctl(EPOLL_CTL_DEL). + * eventpoll_release_file() and epoll_ctl(). */ mutex_lock(&ep->mtx);
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