Don't limit non-nested epoll paths

Commit 28d82dc ("epoll: limit paths") that I did to limit the
number of possible wakeup paths in epoll is causing a few applications
to longer work (dovecot for one).

The original patch is really about limiting the amount of epoll nesting
(since epoll fds can be attached to other fds). Thus, we probably can
allow an unlimited number of paths of depth 1. My current patch limits
it at 1000. And enforce the limits on paths that have a greater depth.

This is captured in: https://bugzilla.redhat.com/show_bug.cgi?id=681578

Signed-off-by: Jason Baron <[email protected]>
Cc: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: jibaron

fs/eventpoll.c

@@ -988,6 +988,10 @@ static int path_count[PATH_ARR_SIZE];
 
 static int path_count_inc(int nests)
 {
+	/* Allow an arbitrary number of depth 1 paths */
+	if (nests == 0)
+		return 0;
+
 	if (++path_count[nests] > path_limits[nests])
 		return -1;
 	return 0;