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Subject[PATCH 4.9 19/54] epoll: replace ->visited/visited_list with generation count
Date
From: Al Viro <viro@zeniv.linux.org.uk>

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>

---
fs/eventpoll.c | 26 +++++++-------------------
1 file changed, 7 insertions(+), 19 deletions(-)

--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -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;
};

/* Wait structure used by the poll hooks */
@@ -267,6 +266,8 @@ static long max_user_watches __read_most
*/
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 __re
/* 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.
@@ -1724,13 +1722,12 @@ static int ep_loop_check_proc(void *priv
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(&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,
@@ -1771,18 +1768,8 @@ static int ep_loop_check_proc(void *priv
*/
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)
@@ -1999,6 +1986,7 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, in
error_tgt_fput:
if (full_check) {
clear_tfile_check_list();
+ loop_check_gen++;
mutex_unlock(&epmutex);
}


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