Bugfix for #745 deadlock with baddr statedump+fork

Fixes #745

Signed-off-by: Paul Woegerer <paul_woegerer@mentor.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/liblttng-ust/lttng-ust-comm.c b/liblttng-ust/lttng-ust-comm.c
index 5df33f5f789e529a86249899b0ff4a2655757c7c..a73808e1128f7b63fbb62422e5f7bccc5115a9b4 100644 (file)
--- a/liblttng-ust/lttng-ust-comm.c
+++ b/liblttng-ust/lttng-ust-comm.c
@@ -86,6 +86,14 @@ 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;
 
@@ -505,8 +513,10 @@ void handle_pending_statedump(struct sock_info *sock_info)
        int ctor_passed = sock_info->constructor_sem_posted;
 
        if (ctor_passed && sock_info->statedump_pending) {
+               pthread_mutex_lock(&ust_fork_mutex);
                sock_info->statedump_pending = 0;
                lttng_handle_pending_statedump(sock_info);
+               pthread_mutex_unlock(&ust_fork_mutex);
        }
 }
 
@@ -1627,6 +1637,9 @@ 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 +1650,9 @@ 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) {