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Commit ff329915 authored by Al Viro's avatar Al Viro Committed by Greg Kroah-Hartman
Browse files

epoll: replace ->visited/visited_list with generation count 



commit 18306c404abe18a0972587a6266830583c60c928 upstream.

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

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 3e3bbc4d

fs/eventpoll.c

+7 −19
Original line number Diff line number Diff line
@@ -222,8 +222,7 @@ struct eventpoll { 
	struct file *file;



	/* used to optimize loop detection check */

	int visited;

	struct list_head visited_list_link;

	u64 gen;



#ifdef CONFIG_NET_RX_BUSY_POLL

	/* used to track busy poll napi_id */
@@ -273,6 +272,8 @@ 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;
@@ -282,9 +283,6 @@ 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.
@@ -1867,13 +1865,12 @@ 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_MAX_NESTS,

					ep_loop_check_proc, epi->ffd.file,
@@ -1914,18 +1911,8 @@ 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, EP_MAX_NESTS,

	return ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS,

			      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)
@@ -2147,6 +2134,7 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd, 
error_tgt_fput:

	if (full_check) {

		clear_tfile_check_list();

		loop_check_gen++;

		mutex_unlock(&epmutex);

	}