[RFC PATCH 12/27] get rid of ep_push_nested()

Al Viro
2020-10-04T02:40:44Z

The only remaining user is loop checking. But there we only need
to check that we have not walked into the epoll we are inserting
into - we are adding an edge to acyclic graph, so any loop being
created will have to pass through the source of that edge.

So we don't need that array of cookies - we have only one eventpoll
to watch out for. RIP ep_push_nested(), along with the cookies
array.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
fs/eventpoll.c | 29 ++++-------------------------
1 file changed, 4 insertions(+), 25 deletions(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 9edea3933790..6b1990b8b9a0 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -254,8 +254,7 @@ static DEFINE_MUTEX(epmutex);
static u64 loop_check_gen = 0;

/* Used to check for epoll file descriptor inclusion loops */
-static void *cookies[EP_MAX_NESTS + 1];
-static int nesting;
+static struct eventpoll *inserting_into;

/* Slab cache used to allocate "struct epitem" */
static struct kmem_cache *epi_cache __read_mostly;
@@ -424,21 +423,6 @@ static inline void ep_set_busy_poll_napi_id(struct epitem *epi)

#endif /* CONFIG_NET_RX_BUSY_POLL */

-static bool ep_push_nested(void *cookie)
-{
- int i;
-
- if (nesting > EP_MAX_NESTS) /* too deep nesting */
- return false;
-
- for (i = 0; i < nesting; i++) {
- if (cookies[i] == cookie) /* loop detected */
- return false;
- }
- cookies[nesting++] = cookie;
- return true;
-}
-
/*
* As described in commit 0ccf831cb lockdep: annotate epoll
* the use of wait queues used by epoll is done in a very controlled
@@ -1885,12 +1869,11 @@ static int ep_loop_check_proc(void *priv, void *cookie, int depth)
ep_tovisit = epi->ffd.file->private_data;
if (ep_tovisit->gen == loop_check_gen)
continue;
- if (!ep_push_nested(ep_tovisit)) {
+ if (ep_tovisit == inserting_into || depth > EP_MAX_NESTS) {
error = -1;
} else {
error = ep_loop_check_proc(epi->ffd.file, ep_tovisit,
depth + 1);
- nesting--;
}
if (error != 0)
break;
@@ -1928,12 +1911,8 @@ static int ep_loop_check_proc(void *priv, void *cookie, int depth)
*/
static int ep_loop_check(struct eventpoll *ep, struct file *file)
{
- int err;
-
- ep_push_nested(ep); // can't fail
- err = ep_loop_check_proc(file, ep, 0);
- nesting--;
- return err;
+ inserting_into = ep;
+ return ep_loop_check_proc(file, ep, 0);
}

static void clear_tfile_check_list(void)
--
2.11.0