From: Willy Tarreau <w@1wt.eu>
Date: Thu, 24 Jun 2021 13:51:12 +0000 (+0200)
Subject: BUG: backend: stop looking for queued connections once there's no more
X-Git-Tag: v2.5-dev1~18
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=19c5581b43eb07c3e413cf1be076bd0b2c2becc7;p=thirdparty%2Fhaproxy.git

BUG: backend: stop looking for queued connections once there's no more

Commit ae0b12ee0 ("MEDIUM: queue: use a trylock on the server's queue")
introduced a hard to trigger bug that's more visible with a single thread:
if a server dequeues a connection and finds another free slot with no
connection to place there, process_srv_queue() will never break out of
the loop. In multi-thread it almost does not happen because other threads
bring new connections.

No backport is needed as it's only in -dev.
---

diff --git a/src/queue.c b/src/queue.c
index b7610d41bd..b7ca163ebb 100644
--- a/src/queue.c
+++ b/src/queue.c
@@ -330,6 +330,7 @@ void process_srv_queue(struct server *s)
 	struct server *ref = s->track ? s->track : s;
 	struct proxy  *p = s->proxy;
 	int maxconn;
+	int stop = 0;
 	int done = 0;
 	int px_ok;
 
@@ -345,13 +346,13 @@ void process_srv_queue(struct server *s)
 	 * for the same server will give up, knowing that at least one of
 	 * them will check the conditions again before quitting.
 	 */
-	while (s->served < (maxconn = srv_dynamic_maxconn(s))) {
+	while (!stop && s->served < (maxconn = srv_dynamic_maxconn(s))) {
 		if (HA_SPIN_TRYLOCK(SERVER_LOCK, &s->queue.lock) != 0)
 			break;
 
 		while (s->served < maxconn) {
-			int ret = pendconn_process_next_strm(s, p, px_ok);
-			if (!ret)
+			stop = !pendconn_process_next_strm(s, p, px_ok);
+			if (stop)
 				break;
 			_HA_ATOMIC_INC(&s->served);
 			done++;