From: Willy Tarreau <w@1wt.eu>
Date: Thu, 30 Jan 2025 15:32:35 +0000 (+0100)
Subject: MEDIUM: epoll: skip reports of stale file descriptors
X-Git-Tag: v3.2-dev5~69
X-Git-Url: http://git.ipfire.org/gitweb/gitweb.cgi?a=commitdiff_plain;h=8235a24782e528b9bf8ca9dd69c0a147556dfcb5;p=thirdparty%2Fhaproxy.git

MEDIUM: epoll: skip reports of stale file descriptors

Now that we can see that some events are reported for older instances
of a file descriptor, let's skip these ones instead of reporting
dangerous events on them. It might possibly qualify as a bug if it
helps fixing strange issues in certain environments, in which case it
can make sense to backport it along with the following recent patches:

  DEBUG: fd: add a counter of takeovers of an FD since it was last opened
  MINOR: fd: add a generation number to file descriptors
  DEBUG: epoll: store and compare the FD's generation count with reported event
---

diff --git a/src/ev_epoll.c b/src/ev_epoll.c
index 02ac0ff95..21770aa35 100644
--- a/src/ev_epoll.c
+++ b/src/ev_epoll.c
@@ -266,7 +266,9 @@ static void _do_poll(struct poller *p, int exp, int wake)
 		fd_gen = _HA_ATOMIC_LOAD(&fdtab[fd].generation);
 
 		if (unlikely(ev_gen != fd_gen)) {
-			/* this is a stale report for an older instance of this FD */
+			/* this is a stale report for an older instance of this FD,
+			 * we must ignore it.
+			 */
 
 			if (_HA_ATOMIC_LOAD(&fdtab[fd].owner)) {
 				ulong tmask = _HA_ATOMIC_LOAD(&fdtab[fd].thread_mask);
@@ -297,6 +299,7 @@ static void _do_poll(struct poller *p, int exp, int wake)
 			} else {
 				COUNT_IF(1, "epoll report of event on a just closed fd (harmless)");
 			}
+			continue;
 		}
 
 		if ((e & EPOLLRDHUP) && !(cur_poller.flags & HAP_POLL_F_RDHUP))