Commit 18306c40 authored by Al Viro's avatar Al Viro
Browse files

epoll: replace ->visited/visited_list with generation count 



removes the need to clear it, along with the races.

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent f8d4f44d

fs/eventpoll.c

+8 −19
Original line number Diff line number Diff line
@@ -218,8 +218,7 @@ struct eventpoll { 
	struct file *file;



	/* used to optimize loop detection check */

	struct list_head visited_list_link;

	int visited;

	u64 gen;



#ifdef CONFIG_NET_RX_BUSY_POLL

	/* used to track busy poll napi_id */
@@ -274,6 +273,8 @@ static long max_user_watches __read_mostly; 
 */

static DEFINE_MUTEX(epmutex);



static u64 loop_check_gen = 0;



/* Used to check for epoll file descriptor inclusion loops */

static struct nested_calls poll_loop_ncalls;
@@ -283,9 +284,6 @@ static struct kmem_cache *epi_cache __read_mostly; 
/* Slab cache used to allocate "struct eppoll_entry" */

static struct kmem_cache *pwq_cache __read_mostly;



/* Visited nodes during ep_loop_check(), so we can unset them when we finish */

static LIST_HEAD(visited_list);



/*

 * List of files with newly added links, where we may need to limit the number

 * of emanating paths. Protected by the epmutex.
@@ -1971,13 +1969,12 @@ static int ep_loop_check_proc(void *priv, void *cookie, int call_nests) 
	struct epitem *epi;



	mutex_lock_nested(&ep->mtx, call_nests + 1);

	ep->visited = 1;

	list_add(&ep->visited_list_link, &visited_list);

	ep->gen = loop_check_gen;

	for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {

		epi = rb_entry(rbp, struct epitem, rbn);

		if (unlikely(is_file_epoll(epi->ffd.file))) {

			ep_tovisit = epi->ffd.file->private_data;

			if (ep_tovisit->visited)

			if (ep_tovisit->gen == loop_check_gen)

				continue;

			error = ep_call_nested(&poll_loop_ncalls,

					ep_loop_check_proc, epi->ffd.file,
@@ -2018,18 +2015,8 @@ static int ep_loop_check_proc(void *priv, void *cookie, int call_nests) 
 */

static int ep_loop_check(struct eventpoll *ep, struct file *file)

{

	int ret;

	struct eventpoll *ep_cur, *ep_next;



	ret = ep_call_nested(&poll_loop_ncalls,

	return ep_call_nested(&poll_loop_ncalls,

			      ep_loop_check_proc, file, ep, current);

	/* clear visited list */

	list_for_each_entry_safe(ep_cur, ep_next, &visited_list,

							visited_list_link) {

		ep_cur->visited = 0;

		list_del(&ep_cur->visited_list_link);

	}

	return ret;

}



static void clear_tfile_check_list(void)
@@ -2199,6 +2186,7 @@ int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds, 
			error = epoll_mutex_lock(&epmutex, 0, nonblock);

			if (error)

				goto error_tgt_fput;

			loop_check_gen++;

			full_check = 1;

			if (is_file_epoll(tf.file)) {

				error = -ELOOP;
@@ -2262,6 +2250,7 @@ int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds, 
error_tgt_fput:

	if (full_check) {

		clear_tfile_check_list();

		loop_check_gen++;

		mutex_unlock(&epmutex);

	}