Fix: take the ust lock around session iteration in statedump

[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 4724fabc0d6a72cf57923cea7e6da44d94563052..256cbdc625ef19f6da306124542a6e0a08ab593f 100644 (file)
--- a/liblttng-ust/lttng-ust-comm.c
+++ b/liblttng-ust/lttng-ust-comm.c
@@ -108,7 +108,8 @@ struct sock_info {
 
        char wait_shm_path[PATH_MAX];
        char *wait_shm_mmap;
-       int session_enabled;
+       /* Keep track of lazy state dump not performed yet. */
+       int statedump_pending;
 };
 
 /* Socket from app (connect) to session daemon (listen) for communication */
@@ -126,7 +127,7 @@ struct sock_info global_apps = {
 
        .wait_shm_path = "/" LTTNG_UST_WAIT_FILENAME,
 
-       .session_enabled = 0,
+       .statedump_pending = 0,
 };
 
 /* TODO: allow global_apps_sock_path override */
@@ -141,7 +142,7 @@ struct sock_info local_apps = {
        .socket = -1,
        .notify_socket = -1,
 
-       .session_enabled = 0,
+       .statedump_pending = 0,
 };
 
 static int wait_poll_fallback;
@@ -387,6 +388,28 @@ int handle_register_done(struct sock_info *sock_info)
        return 0;
 }
 
+/*
+ * Only execute pending statedump after the constructor semaphore has
+ * been posted by each listener thread. This means statedump will only
+ * be performed after the "registration done" command is received from
+ * each session daemon the application is connected to.
+ *
+ * This ensures we don't run into deadlock issues with the dynamic
+ * loader mutex, which is held while the constructor is called and
+ * waiting on the constructor semaphore. All operations requiring this
+ * dynamic loader lock need to be postponed using this mechanism.
+ */
+static
+void handle_pending_statedump(struct sock_info *sock_info)
+{
+       int ctor_passed = sock_info->constructor_sem_posted;
+
+       if (ctor_passed && sock_info->statedump_pending) {
+               sock_info->statedump_pending = 0;
+               lttng_handle_pending_statedump(sock_info);
+       }
+}
+
 static
 int handle_message(struct sock_info *sock_info,
                int sock, struct ustcomm_ust_msg *lum)
@@ -705,18 +728,15 @@ end:
 
 error:
        ust_unlock();
-       return ret;
-}
 
-static
-void handle_pending_statedumps(struct sock_info *sock_info)
-{
-       int ctor_passed = sock_info->constructor_sem_posted;
+       /*
+        * Performed delayed statedump operations outside of the UST
+        * lock. We need to take the dynamic loader lock before we take
+        * the UST lock internally within handle_pending_statedump().
+         */
+       handle_pending_statedump(sock_info);
 
-       if (ctor_passed && sock_info->session_enabled) {
-               sock_info->session_enabled = 0;
-               lttng_handle_pending_statedumps(&lttng_ust_baddr_statedump);
-       }
+       return ret;
 }
 
 static
@@ -1224,8 +1244,6 @@ restart:
                        ret = handle_message(sock_info, sock, &lum);
                        if (ret) {
                                ERR("Error handling message for %s socket", sock_info->name);
-                       } else {
-                               handle_pending_statedumps(sock_info);
                        }
                        continue;
                default:
@@ -1543,5 +1561,5 @@ void ust_after_fork_child(sigset_t *restore_sigset)
 void lttng_ust_sockinfo_session_enabled(void *owner)
 {
        struct sock_info *sock_info = owner;
-       sock_info->session_enabled = 1;
+       sock_info->statedump_pending = 1;
 }