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epoll: replace ->visited/visited_list with generation count

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

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2020-09-10 08:30:05 -04:00
parent f8d4f44df0
commit 18306c404a
1 changed files with 8 additions and 19 deletions
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27
fs/eventpoll.c
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@ -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);
}