Fix: socket connect hang on heavy loads

[lttng-ust.git] / liblttng-ust / lttng-ust-comm.c

diff --git a/liblttng-ust/lttng-ust-comm.c b/liblttng-ust/lttng-ust-comm.c
index a06489fbef8a32bc5d29a12d844278575881a548..1c7584ddd51e84ed3d1d55015467101791bd4657 100644 (file)
--- a/liblttng-ust/lttng-ust-comm.c
+++ b/liblttng-ust/lttng-ust-comm.c
@@ -896,8 +896,6 @@ void *ust_listener_thread(void *arg)
 {
        struct sock_info *sock_info = arg;
        int sock, ret, prev_connect_failed = 0, has_waited = 0;
-       int open_sock[2];
-       int i;
        long timeout;
 
        /* Restart trying to connect to the session daemon */
@@ -935,55 +933,35 @@ restart:
                sock_info->notify_socket = -1;
        }
 
-       /* Register */
-       for (i = 0; i < 2; i++) {
-               ret = ustcomm_connect_unix_sock(sock_info->sock_path);
-               if (ret < 0) {
-                       DBG("Info: sessiond not accepting connections to %s apps socket", sock_info->name);
-                       prev_connect_failed = 1;
-
-                       ust_lock();
+       /*
+        * Register. We need to perform both connect and sending
+        * registration message before doing the next connect otherwise
+        * we may reach unix socket connect queue max limits and block
+        * on the 2nd connect while the session daemon is awaiting the
+        * first connect registration message.
+        */
+       /* Connect cmd socket */
+       ret = ustcomm_connect_unix_sock(sock_info->sock_path);
+       if (ret < 0) {
+               DBG("Info: sessiond not accepting connections to %s apps socket", sock_info->name);
+               prev_connect_failed = 1;
 
-                       if (lttng_ust_comm_should_quit) {
-                               goto quit;
-                       }
+               ust_lock();
 
-                       /*
-                        * If we cannot find the sessiond daemon, don't delay
-                        * constructor execution.
-                        */
-                       ret = handle_register_done(sock_info);
-                       assert(!ret);
-                       ust_unlock();
-                       goto restart;
+               if (lttng_ust_comm_should_quit) {
+                       goto quit;
                }
-               open_sock[i] = ret;
-       }
-
-       sock_info->socket = open_sock[0];
-       sock_info->notify_socket = open_sock[1];
 
-       timeout = get_notify_sock_timeout();
-       if (timeout >= 0) {
                /*
-                * Give at least 10ms to sessiond to reply to
-                * notifications.
+                * If we cannot find the sessiond daemon, don't delay
+                * constructor execution.
                 */
-               if (timeout < 10)
-                       timeout = 10;
-               ret = ustcomm_setsockopt_rcv_timeout(sock_info->notify_socket,
-                               timeout);
-               if (ret < 0) {
-                       WARN("Error setting socket receive timeout");
-               }
-               ret = ustcomm_setsockopt_snd_timeout(sock_info->notify_socket,
-                               timeout);
-               if (ret < 0) {
-                       WARN("Error setting socket send timeout");
-               }
-       } else if (timeout < -1) {
-               WARN("Unsupported timeout value %ld", timeout);
+               ret = handle_register_done(sock_info);
+               assert(!ret);
+               ust_unlock();
+               goto restart;
        }
+       sock_info->socket = ret;
 
        ust_lock();
 
@@ -1019,6 +997,60 @@ restart:
                ust_unlock();
                goto restart;
        }
+
+       ust_unlock();
+
+       /* Connect notify socket */
+       ret = ustcomm_connect_unix_sock(sock_info->sock_path);
+       if (ret < 0) {
+               DBG("Info: sessiond not accepting connections to %s apps socket", sock_info->name);
+               prev_connect_failed = 1;
+
+               ust_lock();
+
+               if (lttng_ust_comm_should_quit) {
+                       goto quit;
+               }
+
+               /*
+                * If we cannot find the sessiond daemon, don't delay
+                * constructor execution.
+                */
+               ret = handle_register_done(sock_info);
+               assert(!ret);
+               ust_unlock();
+               goto restart;
+       }
+       sock_info->notify_socket = ret;
+
+       timeout = get_notify_sock_timeout();
+       if (timeout >= 0) {
+               /*
+                * Give at least 10ms to sessiond to reply to
+                * notifications.
+                */
+               if (timeout < 10)
+                       timeout = 10;
+               ret = ustcomm_setsockopt_rcv_timeout(sock_info->notify_socket,
+                               timeout);
+               if (ret < 0) {
+                       WARN("Error setting socket receive timeout");
+               }
+               ret = ustcomm_setsockopt_snd_timeout(sock_info->notify_socket,
+                               timeout);
+               if (ret < 0) {
+                       WARN("Error setting socket send timeout");
+               }
+       } else if (timeout < -1) {
+               WARN("Unsupported timeout value %ld", timeout);
+       }
+
+       ust_lock();
+
+       if (lttng_ust_comm_should_quit) {
+               goto quit;
+       }
+
        ret = register_to_sessiond(sock_info->notify_socket,
                        USTCTL_SOCKET_NOTIFY);
        if (ret < 0) {