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authorAl Viro <viro@zeniv.linux.org.uk>2020-09-10 08:30:05 -0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2020-10-07 08:02:55 +0200
commita6a47119b527f894409fb3dc6177e05c89085c64 (patch)
tree58463cbd3b4a93101830796022376bd7377790b7
parentbdb43b31e65d418008a7f6718bbd2ca5ee04669a (diff)
epoll: replace ->visited/visited_list with generation count
commit 18306c404abe18a0972587a6266830583c60c928 upstream. removes the need to clear it, along with the races. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--fs/eventpoll.c27
1 files changed, 8 insertions, 19 deletions
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 5207dfc85b78..82ab9a25f12f 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -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);
}