MEDIUM: server: extend refcount for all servers

In a future patch, it will be possible to remove at runtime every
servers, both static and dynamic. This requires to extend the server
refcount for all instances.

First, refcount manipulation functions have been renamed to better
express the API usage.

* srv_refcount_use -> srv_take
The refcount is always initialize to 1 on the server creation in
new_server. It's also incremented for each check/agent configured on a
server instance.

* free_server -> srv_drop
This decrements the refcount and if null, the server is freed, so code
calling it must not use the server reference after it. As a bonus, this
function now returns the next server instance. This is useful when
calling on the server loop without having to save the next pointer
before each invocation.

In these functions, remove the checks that prevent refcount on
non-dynamic servers. Each reference to "dynamic" in variable/function
naming have been eliminated as well.

8 files changed, 28 insertions, 40 deletions

diff --git a/include/haproxy/server-t.h b/include/haproxy/server-t.h
index 02f15fc01..a01081d54 100644
--- a/include/haproxy/server-t.h
+++ b/include/haproxy/server-t.h
@@ -259,7 +259,7 @@ 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 */
+	uint refcount;                          /* refcount used to remove a server at runtime */
 
 	/* The elements below may be changed on every single request by any
 	 * thread, and generally at the same time.
diff --git a/include/haproxy/server.h b/include/haproxy/server.h
index b39be2a1c..99d26ba0d 100644
--- a/include/haproxy/server.h
+++ b/include/haproxy/server.h
@@ -59,8 +59,8 @@ int srv_set_addr_via_libc(struct server *srv, int *err_code);
 int srv_init_addr(void);
 struct server *cli_find_server(struct appctx *appctx, char *arg);
 struct server *new_server(struct proxy *proxy);
-void srv_use_dynsrv(struct server *srv);
-struct server *free_server(struct server *srv);
+void srv_take(struct server *srv);
+struct server *srv_drop(struct server *srv);
 int srv_init_per_thr(struct server *srv);
 
 /* functions related to server name resolution */
diff --git a/src/check.c b/src/check.c
index 4a4e4c770..55f07939b 100644
--- a/src/check.c
+++ b/src/check.c
@@ -1241,13 +1241,13 @@ struct task *process_chk_conn(struct task *t, void *context, unsigned int state)
 	TRACE_LEAVE(CHK_EV_TASK_WAKE, check);
 
 	/* Free the check if set to PURGE. After this, the check instance may be
-	 * freed via the free_server invocation, so it must not be accessed
-	 * after this point.
+	 * freed via the srv_drop invocation, so it must not be accessed after
+	 * this point.
 	 */
 	if (unlikely(check->state & CHK_ST_PURGE)) {
 		free_check(check);
 		if (check->server)
-			free_server(check->server);
+			srv_drop(check->server);
 
 		t = NULL;
 	}
@@ -1688,6 +1688,7 @@ int init_srv_check(struct server *srv)
 		goto out;
 	}
 	srv->check.state |= CHK_ST_CONFIGURED | CHK_ST_ENABLED;
+	srv_take(srv);
 
 	/* Only increment maxsock for servers from the configuration. Dynamic
 	 * servers at the moment are not taken into account for the estimation
@@ -1743,6 +1744,7 @@ int init_srv_agent_check(struct server *srv)
 		srv->agent.inter = srv->check.inter;
 
 	srv->agent.state |= CHK_ST_CONFIGURED | CHK_ST_ENABLED | CHK_ST_AGENT;
+	srv_take(srv);
 
 	/* Only increment maxsock for servers from the configuration. Dynamic
 	 * servers at the moment are not taken into account for the estimation
diff --git a/src/hlua.c b/src/hlua.c
index 4ec28a083..ea9d31cdb 100644
--- a/src/hlua.c
+++ b/src/hlua.c
@@ -11759,10 +11759,10 @@ static void hlua_deinit()
 			lua_close(hlua_states[thr]);
 	}
 
-	free_server(socket_tcp);
+	srv_drop(socket_tcp);
 
 #ifdef USE_OPENSSL
-	free_server(socket_ssl);
+	srv_drop(socket_ssl);
 #endif
 
 	free_proxy(socket_proxy);
diff --git a/src/http_client.c b/src/http_client.c
index 6719ce507..9f06ccc44 100644
--- a/src/http_client.c
+++ b/src/http_client.c
@@ -738,9 +738,9 @@ static int httpclient_init()
 err:
 	ha_alert("httpclient: cannot initialize.\n");
 	free(errmsg);
-	free_server(httpclient_srv_raw);
+	srv_drop(httpclient_srv_raw);
 #ifdef USE_OPENSSL
-	free_server(httpclient_srv_ssl);
+	srv_drop(httpclient_srv_ssl);
 #endif
 	free_proxy(httpclient_proxy);
 	return err_code;
diff --git a/src/proxy.c b/src/proxy.c
index 5d701866b..3391dc90b 100644
--- a/src/proxy.c
+++ b/src/proxy.c
@@ -291,7 +291,7 @@ void free_proxy(struct proxy *p)
 	while (s) {
 		list_for_each_entry(srvdf, &server_deinit_list, list)
 			srvdf->fct(s);
-		s = free_server(s);
+		s = srv_drop(s);
 	}/* end while(s) */
 
 	list_for_each_entry_safe(l, l_next, &p->conf.listeners, by_fe) {
diff --git a/src/server.c b/src/server.c
index 54a569f72..fdce968f0 100644
--- a/src/server.c
+++ b/src/server.c
@@ -2160,6 +2160,8 @@ struct server *new_server(struct proxy *proxy)
 	if (!srv)
 		return NULL;
 
+	srv_take(srv);
+
 	srv->obj_type = OBJ_TYPE_SERVER;
 	srv->proxy = proxy;
 	queue_init(&srv->queue, proxy, srv);
@@ -2196,18 +2198,10 @@ struct server *new_server(struct proxy *proxy)
 	return srv;
 }
 
-/* Increment the dynamic server refcount. */
-void srv_use_dynsrv(struct server *srv)
+/* Increment the server refcount. */
+void srv_take(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);
+	HA_ATOMIC_INC(&srv->refcount);
 }
 
 /* Deallocate a server <srv> and its member. <srv> must be allocated. For
@@ -2215,9 +2209,9 @@ static uint srv_release_dynsrv(struct server *srv)
  * conducted only if the refcount is nul, unless the process is stopping.
  *
  * As a convenience, <srv.next> is returned if srv is not NULL. It may be useful
- * when calling free_server on the list of servers.
+ * when calling srv_drop on the list of servers.
  */
-struct server *free_server(struct server *srv)
+struct server *srv_drop(struct server *srv)
 {
 	struct server *next = NULL;
 
@@ -2230,10 +2224,8 @@ struct server *free_server(struct server *srv)
 	 * server when reaching zero.
 	 */
 	if (likely(!(global.mode & MODE_STOPPING))) {
-		if (srv->flags & SRV_F_DYNAMIC) {
-			if (srv_release_dynsrv(srv))
-				goto end;
-		}
+		if (HA_ATOMIC_SUB_FETCH(&srv->refcount, 1))
+			goto end;
 	}
 
 	task_destroy(srv->warmup);
@@ -4590,7 +4582,6 @@ static int cli_parse_add_server(char **args, char *payload, struct appctx *appct
 			goto out;
 
 		srv->check.state &= ~CHK_ST_ENABLED;
-		srv_use_dynsrv(srv);
 	}
 
 	if (srv->do_agent) {
@@ -4598,7 +4589,6 @@ static int cli_parse_add_server(char **args, char *payload, struct appctx *appct
 			goto out;
 
 		srv->agent.state &= ~CHK_ST_ENABLED;
-		srv_use_dynsrv(srv);
 	}
 
 	/* Attach the server to the end of the proxy linked list. Note that this
@@ -4649,7 +4639,6 @@ 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();
 
 	/* Start the check task. The server must be fully initialized.
@@ -4701,7 +4690,7 @@ out:
 		cli_err(appctx, usermsgs_str());
 
 	if (srv)
-		free_server(srv);
+		srv_drop(srv);
 
 	return 1;
 }
@@ -4823,7 +4812,7 @@ static int cli_parse_delete_server(char **args, char *payload, struct appctx *ap
 	thread_release();
 
 	ha_notice("Server deleted.\n");
-	free_server(srv);
+	srv_drop(srv);
 
 	cli_msg(appctx, LOG_INFO, "Server deleted.");
 
diff --git a/src/stats.c b/src/stats.c
index 8140d87f9..35415b309 100644
--- a/src/stats.c
+++ b/src/stats.c
@@ -3113,17 +3113,15 @@ int stats_dump_proxy_to_buffer(struct stream_interface *si, struct htx *htx,
 	case STAT_PX_ST_SV:
 		/* obj2 points to servers list as initialized above.
 		 *
-		 * A dynamic server may be removed during the stats dumping.
+		 * A server may be removed during the stats dumping.
 		 * Temporarily increment its refcount to prevent its
 		 * anticipated cleaning. Call free_server to release it.
 		 */
 		for (; appctx->ctx.stats.obj2 != NULL;
-		       appctx->ctx.stats.obj2 =
-		        (!(sv->flags & SRV_F_DYNAMIC)) ? sv->next : free_server(sv)) {
+		       appctx->ctx.stats.obj2 = srv_drop(sv)) {
 
 			sv = appctx->ctx.stats.obj2;
-			if (sv->flags & SRV_F_DYNAMIC)
-				srv_use_dynsrv(sv);
+			srv_take(sv);
 
 			if (htx) {
 				if (htx_almost_full(htx))
@@ -3136,8 +3134,7 @@ int stats_dump_proxy_to_buffer(struct stream_interface *si, struct htx *htx,
 
 			if (appctx->ctx.stats.flags & STAT_BOUND) {
 				if (!(appctx->ctx.stats.type & (1 << STATS_TYPE_SV))) {
-					if (sv->flags & SRV_F_DYNAMIC)
-						free_server(appctx->ctx.stats.obj2);
+					srv_drop(sv);
 					break;
 				}