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: Tony Battersby <tonyb@cybernetics.com>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 64c5503..744377c 100644 (file)
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -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)