Commit 85353e91 authored by Al Viro's avatar Al Viro
Browse files

ep_insert(): we only need tep->mtx around the insertion itself 



We do need ep->mtx (and we are holding it all along), but that's
the lock on the epoll we are inserting into; locking of the
epoll being inserted is not needed for most of that work -
as the matter of fact, we only need it to provide barriers
for the fastpath check (for now).

Move taking and releasing it into ep_insert().  The caller
(do_epoll_ctl()) doesn't need to bother with that at all.
Moreover, that way we kill the kludge in ep_item_poll() - now
it's always called with tep unlocked.

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent e3e096e7

fs/eventpoll.c

+10 −18
Original line number Diff line number Diff line
@@ -731,8 +731,6 @@ static int ep_eventpoll_release(struct inode *inode, struct file *file) 


static __poll_t ep_read_events_proc(struct eventpoll *ep, struct list_head *head,

			       int depth);

static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,

				 poll_table *pt);



/*

 * Differs from ep_eventpoll_poll() in that internal callers already have
@@ -745,7 +743,6 @@ static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt, 
	struct eventpoll *ep;

	LIST_HEAD(txlist);

	__poll_t res;

	bool locked;



	pt->_key = epi->event.events;

	if (!is_file_epoll(epi->ffd.file))
@@ -754,14 +751,10 @@ static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt, 
	ep = epi->ffd.file->private_data;

	poll_wait(epi->ffd.file, &ep->poll_wait, pt);



	// kludge: ep_insert() calls us with ep->mtx already locked

	locked = pt && (pt->_qproc == ep_ptable_queue_proc);

	if (!locked)

	mutex_lock_nested(&ep->mtx, depth);

	ep_start_scan(ep, &txlist);

	res = ep_read_events_proc(ep, &txlist, depth + 1);

	ep_done_scan(ep, &txlist);

	if (!locked)

	mutex_unlock(&ep->mtx);

	return res & epi->event.events;

}
@@ -1365,6 +1358,10 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event, 
	long user_watches;

	struct epitem *epi;

	struct ep_pqueue epq;

	struct eventpoll *tep = NULL;



	if (is_file_epoll(tfile))

		tep = tfile->private_data;



	lockdep_assert_irqs_enabled();
@@ -1394,6 +1391,8 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event, 


	atomic_long_inc(&ep->user->epoll_watches);



	if (tep)

		mutex_lock_nested(&tep->mtx, 1);

	/* Add the current item to the list of active epoll hook for this file */

	spin_lock(&tfile->f_lock);

	list_add_tail_rcu(&epi->fllink, &tfile->f_ep_links);
@@ -1404,6 +1403,8 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event, 
	 * protected by "mtx", and ep_insert() is called with "mtx" held.

	 */

	ep_rbtree_insert(ep, epi);

	if (tep)

		mutex_unlock(&tep->mtx);



	/* now check if we've created too many backpaths */

	if (unlikely(full_check && reverse_path_check())) {
@@ -2034,13 +2035,6 @@ int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds, 
			error = epoll_mutex_lock(&ep->mtx, 0, nonblock);

			if (error)

				goto error_tgt_fput;

			if (is_file_epoll(tf.file)) {

				error = epoll_mutex_lock(&tep->mtx, 1, nonblock);

				if (error) {

					mutex_unlock(&ep->mtx);

					goto error_tgt_fput;

				}

			}

		}

	}
@@ -2076,8 +2070,6 @@ int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds, 
			error = -ENOENT;

		break;

	}

	if (tep != NULL)

		mutex_unlock(&tep->mtx);

	mutex_unlock(&ep->mtx);



error_tgt_fput: