X-Git-Url: http://git.lttng.org./?a=blobdiff_plain;f=liblttng-ust%2Flttng-ust-comm.c;h=3df2adc6f96e0b0b16189efe6497509ea845e3da;hb=2932a87f05ceaf44c3a0b51fa6bdecd4b13c113d;hp=5df33f5f789e529a86249899b0ff4a2655757c7c;hpb=d58d145447ffcc9497801769e1fe754b30dca5b8;p=lttng-ust.git

diff --git a/liblttng-ust/lttng-ust-comm.c b/liblttng-ust/lttng-ust-comm.c
index 5df33f5f..3df2adc6 100644
--- a/liblttng-ust/lttng-ust-comm.c
+++ b/liblttng-ust/lttng-ust-comm.c
@@ -68,9 +68,14 @@ static int initialized;
  *
  * ust_exit_mutex must never nest in ust_mutex.
  *
+ * ust_fork_mutex must never nest in ust_mutex.
+ *
  * ust_mutex_nest is a per-thread nesting counter, allowing the perf
  * counter lazy initialization called by events within the statedump,
  * which traces while the ust_mutex is held.
+ *
+ * ust_lock nests within the dynamic loader lock (within glibc) because
+ * it is taken within the library constructor.
  */
 static pthread_mutex_t ust_mutex = PTHREAD_MUTEX_INITIALIZER;
 
@@ -86,6 +91,14 @@ static DEFINE_URCU_TLS(int, ust_mutex_nest);
  */
 static pthread_mutex_t ust_exit_mutex = PTHREAD_MUTEX_INITIALIZER;
 
+/*
+ * ust_fork_mutex protects base address statedump tracing against forks. It
+ * prevents the dynamic loader lock to be taken (by base address statedump
+ * tracing) while a fork is happening, thus preventing deadlock issues with
+ * the dynamic loader lock.
+ */
+static pthread_mutex_t ust_fork_mutex = PTHREAD_MUTEX_INITIALIZER;
+
 /* Should the ust comm thread quit ? */
 static int lttng_ust_comm_should_quit;
 
@@ -506,7 +519,9 @@ void handle_pending_statedump(struct sock_info *sock_info)
 
 	if (ctor_passed && sock_info->statedump_pending) {
 		sock_info->statedump_pending = 0;
+		pthread_mutex_lock(&ust_fork_mutex);
 		lttng_handle_pending_statedump(sock_info);
+		pthread_mutex_unlock(&ust_fork_mutex);
 	}
 }
 
@@ -1627,6 +1642,9 @@ void ust_before_fork(sigset_t *save_sigset)
 	if (ret == -1) {
 		PERROR("sigprocmask");
 	}
+
+	pthread_mutex_lock(&ust_fork_mutex);
+
 	ust_lock_nocheck();
 	rcu_bp_before_fork();
 }
@@ -1637,6 +1655,9 @@ static void ust_after_fork_common(sigset_t *restore_sigset)
 
 	DBG("process %d", getpid());
 	ust_unlock();
+
+	pthread_mutex_unlock(&ust_fork_mutex);
+
 	/* Restore signals */
 	ret = sigprocmask(SIG_SETMASK, restore_sigset, NULL);
 	if (ret == -1) {