+ goto end;
+ }
+
+ __lookup_session_by_app(usess, app, &iter);
+ node = lttng_ht_iter_get_node_u64(&iter);
+ if (node == NULL) {
+ /* Session is being or is deleted. */
+ goto end;
+ }
+ ua_sess = caa_container_of(node, struct ust_app_session, node);
+
+ health_code_update();
+ destroy_app_session(app, ua_sess);
+
+ health_code_update();
+
+ /* Quiescent wait after stopping trace */
+ pthread_mutex_lock(&app->sock_lock);
+ ret = ustctl_wait_quiescent(app->sock);
+ pthread_mutex_unlock(&app->sock_lock);
+ if (ret < 0 && ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+ ERR("UST app wait quiescent failed for app pid %d ret %d",
+ app->pid, ret);
+ }
+end:
+ rcu_read_unlock();
+ health_code_update();
+ return 0;
+}
+
+/*
+ * Start tracing for the UST session.
+ */
+int ust_app_start_trace_all(struct ltt_ust_session *usess)
+{
+ int ret = 0;
+ struct lttng_ht_iter iter;
+ struct ust_app *app;
+
+ DBG("Starting all UST traces");
+
+ rcu_read_lock();
+
+ /*
+ * In a start-stop-start use-case, we need to clear the quiescent state
+ * of each channel set by the prior stop command, thus ensuring that a
+ * following stop or destroy is sure to grab a timestamp_end near those
+ * operations, even if the packet is empty.
+ */
+ (void) ust_app_clear_quiescent_session(usess);
+
+ cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
+ ret = ust_app_start_trace(usess, app);
+ if (ret < 0) {
+ /* Continue to next apps even on error */
+ continue;
+ }
+ }
+
+ rcu_read_unlock();
+
+ return 0;
+}
+
+/*
+ * Start tracing for the UST session.
+ * Called with UST session lock held.
+ */
+int ust_app_stop_trace_all(struct ltt_ust_session *usess)
+{
+ int ret = 0;
+ struct lttng_ht_iter iter;
+ struct ust_app *app;
+
+ DBG("Stopping all UST traces");
+
+ rcu_read_lock();
+
+ cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
+ ret = ust_app_stop_trace(usess, app);
+ if (ret < 0) {
+ /* Continue to next apps even on error */
+ continue;
+ }
+ }
+
+ (void) ust_app_flush_session(usess);
+
+ rcu_read_unlock();
+
+ return 0;
+}
+
+/*
+ * Destroy app UST session.
+ */
+int ust_app_destroy_trace_all(struct ltt_ust_session *usess)
+{
+ int ret = 0;
+ struct lttng_ht_iter iter;
+ struct ust_app *app;
+
+ DBG("Destroy all UST traces");
+
+ rcu_read_lock();
+
+ cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
+ ret = destroy_trace(usess, app);
+ if (ret < 0) {
+ /* Continue to next apps even on error */
+ continue;
+ }