From: Amaury Denoyelle <adenoyelle@haproxy.com>
Date: Mon, 2 Aug 2021 13:50:00 +0000 (+0200)
Subject: MINOR: server: implement a refcount for dynamic servers
X-Git-Tag: v2.5-dev4~58
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=d6b7080cecee3450bbad8fbd5d9b100be0a2d13d;p=thirdparty%2Fhaproxy.git

MINOR: server: implement a refcount for dynamic servers

It is necessary to have a refcount mechanism on dynamic servers to be
able to enable check support. Indeed, when deleting a dynamic server
with check activated, the check will be asynchronously removed. This is
mandatory to properly free the check resources in a thread-safe manner.
The server instance must be kept alive for this.
---

diff --git a/include/haproxy/server-t.h b/include/haproxy/server-t.h
index 6772db2b04..02f15fc01a 100644
--- a/include/haproxy/server-t.h
+++ b/include/haproxy/server-t.h
@@ -259,6 +259,8 @@ struct server {
 	unsigned cumulative_weight;		/* weight of servers prior to this one in the same group, for chash balancing */
 	int maxqueue;				/* maximum number of pending connections allowed */
 
+	uint refcount_dynsrv;                   /* refcount used for dynamic servers */
+
 	/* The elements below may be changed on every single request by any
 	 * thread, and generally at the same time.
 	 */
diff --git a/src/server.c b/src/server.c
index 9895257616..84b9cd25a8 100644
--- a/src/server.c
+++ b/src/server.c
@@ -2196,10 +2196,32 @@ struct server *new_server(struct proxy *proxy)
 	return srv;
 }
 
+/* Increment the dynamic server refcount. */
+static void srv_use_dynsrv(struct server *srv)
+{
+	BUG_ON(!(srv->flags & SRV_F_DYNAMIC));
+	HA_ATOMIC_INC(&srv->refcount_dynsrv);
+}
+
+/* Decrement the dynamic server refcount. */
+static uint srv_release_dynsrv(struct server *srv)
+{
+	BUG_ON(!(srv->flags & SRV_F_DYNAMIC));
+	return HA_ATOMIC_SUB_FETCH(&srv->refcount_dynsrv, 1);
+}
+
 /* Deallocate a server <srv> and its member. <srv> must be allocated.
  */
 void free_server(struct server *srv)
 {
+	/* For dynamic servers, decrement the reference counter. Only free the
+	 * server when reaching zero.
+	 */
+	if (srv->flags & SRV_F_DYNAMIC) {
+		if (srv_release_dynsrv(srv))
+			return;
+	}
+
 	task_destroy(srv->warmup);
 	task_destroy(srv->srvrq_check);
 
@@ -4590,6 +4612,7 @@ static int cli_parse_add_server(char **args, char *payload, struct appctx *appct
 	ebis_insert(&be->conf.used_server_name, &srv->conf.name);
 	ebis_insert(&be->used_server_addr, &srv->addr_node);
 
+	srv_use_dynsrv(srv);
 	thread_release();
 
 	ha_notice("New server registered.\n");