glusterd: avoid starting the same brick twice

There was a race in glusterd code that could cause that two threads
start the same brick at the same time. One of the bricks will fail
because it will detect the other brick running. Depending on which
brick fails, glusterd will report a start failure and mark the brick
as stopped even if it's running.

The problem is caused by an attempt to connect to a brick that's being
started by another thread. If the brick is not fully initialized, it
will refuse all connection attempts. When this happens, glusterd receives
a disconnection notification, which forcibly marks the brick as stopped.

Now, if another attempt to start the same brick happens, it will believe
that the brick is stopped and it will start it again. If this happens
very soon after the first start attempt, the checks done to see if the
brick is already running will still fail, triggering the start of the
brick process again. One of the bricks will fail to initialize and will
report an error. If the failed one is processed by glusterd in the
second place, the brick will be marked as stopped, even though the
process is actually there and working.

Fixes: #4080
Signed-off-by: Xavi Hernandez <[email protected]>

xlators/mgmt/glusterd/src/glusterd-handler.c

@@ -6358,53 +6358,62 @@ __glusterd_brick_rpc_notify(struct rpc_clnt *rpc, void *mydata,
                                     brickinfo->path);
                 break;
             }
-            if (glusterd_is_brick_started(brickinfo)) {
-                gf_msg(this->name, GF_LOG_INFO, 0, GD_MSG_BRICK_DISCONNECTED,
-                       "Brick %s:%s has disconnected from glusterd.",
-                       brickinfo->hostname, brickinfo->path);
 
-                ret = get_volinfo_from_brickid(brickid, &volinfo);
+            if (!glusterd_is_brick_started(brickinfo)) {
+                /* If the brick is already GF_BRICK_STOPPED, there's no need to
+                 * do anything else. However, if the brick is GF_BRICK_STARTING
+                 * or GF_BRICK_STOPPING, it's better to not touch anything since
+                 * there's another thread already managing the brick.
+                 *
+                 * This may happen when, during the start of a brick, another
+                 * thread attempts to connect to it. Since the unix socket name
+                 * is already present in brickinfo, it will attempt to connect.
+                 * However the brick may still be initializing and not accepting
+                 * connections, so the connection attempt will be rejected,
+                 * triggering the RPC_CLNT_DISCONNECT event. */
+                break;
+            }
+
+            gf_msg(this->name, GF_LOG_INFO, 0, GD_MSG_BRICK_DISCONNECTED,
+                   "Brick %s:%s has disconnected from glusterd.",
+                   brickinfo->hostname, brickinfo->path);
+
+            ret = get_volinfo_from_brickid(brickid, &volinfo);
+            if (ret) {
+                gf_msg(this->name, GF_LOG_ERROR, 0, GD_MSG_VOLINFO_GET_FAIL,
+                       "Failed to get volinfo from brickid(%s)", brickid);
+                goto out;
+            }
+            gf_event(EVENT_BRICK_DISCONNECTED, "peer=%s;volume=%s;brick=%s",
+                     brickinfo->hostname, volinfo->volname, brickinfo->path);
+            /* In case of an abrupt shutdown of a brick PMAP_SIGNOUT
+             * event is not received by glusterd which can lead to a
+             * stale port entry in glusterd, so forcibly clean up
+             * the same if the process is not running sometime
+             * gf_is_service_running true so to ensure about brick instance
+             * call search_brick_path_from_proc
+             */
+            GLUSTERD_GET_BRICK_PIDFILE(pidfile, volinfo, brickinfo, conf);
+            is_service_running = gf_is_service_running(pidfile, &pid);
+            if (pid > 0)
+                brickpath = search_brick_path_from_proc(pid, brickinfo->path);
+            if (!is_service_running || !brickpath) {
+                ret = pmap_port_remove(this, brickinfo->port, brickinfo->path,
+                                       NULL, _gf_true);
                 if (ret) {
-                    gf_msg(this->name, GF_LOG_ERROR, 0, GD_MSG_VOLINFO_GET_FAIL,
-                           "Failed to get volinfo from "
-                           "brickid(%s)",
-                           brickid);
-                    goto out;
-                }
-                gf_event(EVENT_BRICK_DISCONNECTED, "peer=%s;volume=%s;brick=%s",
-                         brickinfo->hostname, volinfo->volname,
-                         brickinfo->path);
-                /* In case of an abrupt shutdown of a brick PMAP_SIGNOUT
-                 * event is not received by glusterd which can lead to a
-                 * stale port entry in glusterd, so forcibly clean up
-                 * the same if the process is not running sometime
-                 * gf_is_service_running true so to ensure about brick instance
-                 * call search_brick_path_from_proc
-                 */
-                GLUSTERD_GET_BRICK_PIDFILE(pidfile, volinfo, brickinfo, conf);
-                is_service_running = gf_is_service_running(pidfile, &pid);
-                if (pid > 0)
-                    brickpath = search_brick_path_from_proc(pid,
-                                                            brickinfo->path);
-                if (!is_service_running || !brickpath) {
-                    ret = pmap_port_remove(this, brickinfo->port,
-                                           brickinfo->path, NULL, _gf_true);
-                    if (ret) {
-                        gf_msg(this->name, GF_LOG_WARNING,
-                               GD_MSG_PMAP_REGISTRY_REMOVE_FAIL, 0,
-                               "Failed to remove pmap "
-                               "registry for port %d for "
-                               "brick %s",
-                               brickinfo->port, brickinfo->path);
-                        ret = 0;
-                    }
+                    gf_msg(this->name, GF_LOG_WARNING,
+                           GD_MSG_PMAP_REGISTRY_REMOVE_FAIL, 0,
+                           "Failed to remove pmap registry for port %d for "
+                           "brick %s",
+                           brickinfo->port, brickinfo->path);
+                    ret = 0;
                 }
             }
 
             if (brickpath)
                 GF_FREE(brickpath);
 
-            if (is_brick_mx_enabled() && glusterd_is_brick_started(brickinfo)) {
+            if (is_brick_mx_enabled()) {
                 brick_proc = brickinfo->brick_proc;
                 if (!brick_proc)
                     break;