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Commit e057e15f authored by Tony Battersby's avatar Tony Battersby Committed by Linus Torvalds
Browse files

epoll: clean up ep_modify 



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_proc(), and this is protected by ep->mtx instead of
ep->lock.  Also update the comment for mutex_lock() at the top of
ep_scan_ready_list(), 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: default avatarTony Battersby <tonyb@cybernetics.com>
Acked-by: default avatarDavide Libenzi <davidel@xmailserver.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d1bc90dd

fs/eventpoll.c

+7 −12
Original line number Diff line number Diff line
@@ -435,7 +435,7 @@ static int ep_scan_ready_list(struct eventpoll *ep, 


	/*

	 * 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);
@@ -972,15 +972,14 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_even 
{

	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
@@ -988,16 +987,12 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_even 
	 */

	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);
@@ -1007,8 +1002,8 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_even 
			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)