Fix: baddr deadlock with lttng-ust destructor

[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 256cbdc625ef19f6da306124542a6e0a08ab593f..c6640954c6aa77d34203cbc6cda8c32eae34d7c6 100644 (file)
--- a/liblttng-ust/lttng-ust-comm.c
+++ b/liblttng-ust/lttng-ust-comm.c
@@ -63,11 +63,55 @@ static int initialized;
  * The ust_lock/ust_unlock lock is used as a communication thread mutex.
  * Held when handling a command, also held by fork() to deal with
  * removal of threads, and by exit path.
+ *
+ * The UST lock is the centralized mutex across UST tracing control and
+ * probe registration.
+ *
+ * ust_exit_mutex must never nest in ust_mutex.
+ */
+static pthread_mutex_t ust_mutex = PTHREAD_MUTEX_INITIALIZER;
+
+/*
+ * ust_exit_mutex protects thread_active variable wrt thread exit. It
+ * cannot be done by ust_mutex because pthread_cancel(), which takes an
+ * internal libc lock, cannot nest within ust_mutex.
+ *
+ * It never nests within a ust_mutex.
  */
+static pthread_mutex_t ust_exit_mutex = PTHREAD_MUTEX_INITIALIZER;
 
 /* Should the ust comm thread quit ? */
 static int lttng_ust_comm_should_quit;
 
+/*
+ * Return 0 on success, -1 if should quilt.
+ * The lock is taken in both cases.
+ */
+int ust_lock(void)
+{
+       pthread_mutex_lock(&ust_mutex);
+       if (lttng_ust_comm_should_quit) {
+               return -1;
+       } else {
+               return 0;
+       }
+}
+
+/*
+ * ust_lock_nocheck() can be used in constructors/destructors, because
+ * they are already nested within the dynamic loader lock, and therefore
+ * have exclusive access against execution of liblttng-ust destructor.
+ */
+void ust_lock_nocheck(void)
+{
+       pthread_mutex_lock(&ust_mutex);
+}
+
+void ust_unlock(void)
+{
+       pthread_mutex_unlock(&ust_mutex);
+}
+
 /*
  * Wait for either of these before continuing to the main
  * program:
@@ -420,11 +464,9 @@ int handle_message(struct sock_info *sock_info,
        union ust_args args;
        ssize_t len;
 
-       ust_lock();
-
        memset(&lur, 0, sizeof(lur));
 
-       if (lttng_ust_comm_should_quit) {
+       if (ust_lock()) {
                ret = -LTTNG_UST_ERR_EXITING;
                goto end;
        }
@@ -983,8 +1025,7 @@ void wait_for_sessiond(struct sock_info *sock_info)
 {
        int ret;
 
-       ust_lock();
-       if (lttng_ust_comm_should_quit) {
+       if (ust_lock()) {
                goto quit;
        }
        if (wait_poll_fallback) {
@@ -1089,9 +1130,7 @@ restart:
                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) {
+               if (ust_lock()) {
                        goto quit;
                }
 
@@ -1106,9 +1145,7 @@ restart:
        }
        sock_info->socket = ret;
 
-       ust_lock();
-
-       if (lttng_ust_comm_should_quit) {
+       if (ust_lock()) {
                goto quit;
        }
 
@@ -1149,9 +1186,7 @@ restart:
                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) {
+               if (ust_lock()) {
                        goto quit;
                }
 
@@ -1188,9 +1223,7 @@ restart:
                WARN("Unsupported timeout value %ld", timeout);
        }
 
-       ust_lock();
-
-       if (lttng_ust_comm_should_quit) {
+       if (ust_lock()) {
                goto quit;
        }
 
@@ -1221,8 +1254,7 @@ restart:
                switch (len) {
                case 0: /* orderly shutdown */
                        DBG("%s lttng-sessiond has performed an orderly shutdown", sock_info->name);
-                       ust_lock();
-                       if (lttng_ust_comm_should_quit) {
+                       if (ust_lock()) {
                                goto quit;
                        }
                        /*
@@ -1261,8 +1293,7 @@ restart:
 
        }
 end:
-       ust_lock();
-       if (lttng_ust_comm_should_quit) {
+       if (ust_lock()) {
                goto quit;
        }
        /* Cleanup socket handles before trying to reconnect */
@@ -1271,8 +1302,11 @@ end:
        goto restart;   /* try to reconnect */
 
 quit:
-       sock_info->thread_active = 0;
        ust_unlock();
+
+       pthread_mutex_lock(&ust_exit_mutex);
+       sock_info->thread_active = 0;
+       pthread_mutex_unlock(&ust_exit_mutex);
        return NULL;
 }
 
@@ -1346,7 +1380,7 @@ void __attribute__((constructor)) lttng_ust_init(void)
                ERR("pthread_attr_setdetachstate: %s", strerror(ret));
        }
 
-       ust_lock();
+       ust_lock_nocheck();
        ret = pthread_create(&global_apps.ust_listener, &thread_attr,
                        ust_listener_thread, &global_apps);
        if (ret) {
@@ -1356,7 +1390,7 @@ void __attribute__((constructor)) lttng_ust_init(void)
        ust_unlock();
 
        if (local_apps.allowed) {
-               ust_lock();
+               ust_lock_nocheck();
                ret = pthread_create(&local_apps.ust_listener, &thread_attr,
                                ust_listener_thread, &local_apps);
                if (ret) {
@@ -1447,9 +1481,11 @@ void __attribute__((destructor)) lttng_ust_exit(void)
         * mutexes to ensure it is not in a mutex critical section when
         * pthread_cancel is later called.
         */
-       ust_lock();
+       ust_lock_nocheck();
        lttng_ust_comm_should_quit = 1;
+       ust_unlock();
 
+       pthread_mutex_lock(&ust_exit_mutex);
        /* cancel threads */
        if (global_apps.thread_active) {
                ret = pthread_cancel(global_apps.ust_listener);
@@ -1469,7 +1505,7 @@ void __attribute__((destructor)) lttng_ust_exit(void)
                        local_apps.thread_active = 0;
                }
        }
-       ust_unlock();
+       pthread_mutex_unlock(&ust_exit_mutex);
 
        /*
         * Do NOT join threads: use of sys_futex makes it impossible to
@@ -1508,7 +1544,7 @@ void ust_before_fork(sigset_t *save_sigset)
        if (ret == -1) {
                PERROR("sigprocmask");
        }
-       ust_lock();
+       ust_lock_nocheck();
        rcu_bp_before_fork();
 }