Fix: perform TLS fixup of nest count outside of UST mutex

[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 5e738b06cf6eee5b539f4f507ba97817525a8fbf..2c787f75b88ae3f32b27582bcaeb3607b52d4083 100644 (file)
--- a/liblttng-ust/lttng-ust-comm.c
+++ b/liblttng-ust/lttng-ust-comm.c
@@ -78,6 +78,12 @@ static sem_t constructor_wait;
  */
 static int sem_count = { 2 };
 
+/*
+ * Counting nesting within lttng-ust. Used to ensure that calling fork()
+ * from liblttng-ust does not execute the pre/post fork handlers.
+ */
+static int __thread lttng_ust_nest_count;
+
 /*
  * Info about socket and associated listener thread.
  */
@@ -130,6 +136,15 @@ extern void ltt_ring_buffer_client_overwrite_exit(void);
 extern void ltt_ring_buffer_client_discard_exit(void);
 extern void ltt_ring_buffer_metadata_client_exit(void);
 
+/*
+ * Force a read (imply TLS fixup for dlopen) of TLS variables.
+ */
+static
+void lttng_fixup_nest_count_tls(void)
+{
+       asm volatile ("" : : "m" (lttng_ust_nest_count));
+}
+
 static
 int setup_local_apps(void)
 {
@@ -469,7 +484,9 @@ int get_wait_shm(struct sock_info *sock_info, size_t mmap_size)
         * If the open failed because the file did not exist, try
         * creating it ourself.
         */
+       lttng_ust_nest_count++;
        pid = fork();
+       lttng_ust_nest_count--;
        if (pid > 0) {
                int status;
 
@@ -852,6 +869,7 @@ void __attribute__((constructor)) lttng_ust_init(void)
        lttng_fixup_event_tls();
        lttng_fixup_ringbuffer_tls();
        lttng_fixup_vtid_tls();
+       lttng_fixup_nest_count_tls();
 
        /*
         * We want precise control over the order in which we construct
@@ -1019,6 +1037,8 @@ void ust_before_fork(sigset_t *save_sigset)
        sigset_t all_sigs;
        int ret;
 
+       if (lttng_ust_nest_count)
+               return;
        /* Disable signals */
        sigfillset(&all_sigs);
        ret = sigprocmask(SIG_BLOCK, &all_sigs, save_sigset);
@@ -1044,6 +1064,8 @@ static void ust_after_fork_common(sigset_t *restore_sigset)
 
 void ust_after_fork_parent(sigset_t *restore_sigset)
 {
+       if (lttng_ust_nest_count)
+               return;
        DBG("process %d", getpid());
        rcu_bp_after_fork_parent();
        /* Release mutexes and reenable signals */
@@ -1061,6 +1083,8 @@ void ust_after_fork_parent(sigset_t *restore_sigset)
  */
 void ust_after_fork_child(sigset_t *restore_sigset)
 {
+       if (lttng_ust_nest_count)
+               return;
        DBG("process %d", getpid());
        /* Release urcu mutexes */
        rcu_bp_after_fork_child();