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Subject[PATCH 5/6] [2.6.29] 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(), 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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