From 79a88ba3d09f7e2b73ae27cb5d24cc087a548fa6 Mon Sep 17 00:00:00 2001 From: Amaury Denoyelle Date: Mon, 17 May 2021 10:47:18 +0200 Subject: [PATCH] BUG/MAJOR: server: prevent deadlock when using 'set maxconn server' A deadlock is possible with 'set maxconn server' command, if there is pending connection ready to be dequeued. This is caused by the locking of server spinlock in both cli_parse_set_maxconn_server and process_srv_queue. Fix this by reducing the scope of the server lock into server_parse_maxconn_change_request. If connection are dequeued, the lock is taken a second time. This can be seen as suboptimal but as it happens only during 'set maxconn server' it can be considered as tolerable. This issue was reported on the mailing list, for the 1.8.x branch. It must be backported up to the 1.8. --- src/server.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/src/server.c b/src/server.c index fa1d9d6..49bd545 100644 --- a/src/server.c +++ b/src/server.c @@ -1800,11 +1800,13 @@ const char *server_parse_maxconn_change_request(struct server *sv, else if (end[0] != '\0') return "Trailing garbage in maxconn string"; + HA_SPIN_LOCK(SERVER_LOCK, &sv->lock); if (sv->maxconn == sv->minconn) { // static maxconn sv->maxconn = sv->minconn = v; } else { // dynamic maxconn sv->maxconn = v; } + HA_SPIN_UNLOCK(SERVER_LOCK, &sv->lock); if (may_dequeue_tasks(sv, sv->proxy)) process_srv_queue(sv); @@ -4141,14 +4143,10 @@ static int cli_parse_set_maxconn_server(char **args, char *payload, struct appct if (!sv) return 1; - HA_SPIN_LOCK(SERVER_LOCK, &sv->lock); - warning = server_parse_maxconn_change_request(sv, args[4]); if (warning) cli_err(appctx, warning); - HA_SPIN_UNLOCK(SERVER_LOCK, &sv->lock); - return 1; } -- 1.7.10.4