Fix: sessiond: ust-app: account for the event notification pipes fds

[lttng-tools.git] / src / bin / lttng-sessiond / ust-app.c

diff --git a/src/bin/lttng-sessiond/ust-app.c b/src/bin/lttng-sessiond/ust-app.c
index 38d1d78713e6446dca9b55b001ccfbee376c88b3..5ab55ec29d3718b83a67135e3b6a155af8c74bfb 100644 (file)
--- a/src/bin/lttng-sessiond/ust-app.c
+++ b/src/bin/lttng-sessiond/ust-app.c
@@ -952,6 +952,7 @@ void delete_ust_app(struct ust_app *app)
        struct ust_app_session *ua_sess, *tmp_ua_sess;
        struct lttng_ht_iter iter;
        struct ust_app_event_notifier_rule *event_notifier_rule;
+       bool event_notifier_write_fd_is_open;
 
        /*
         * The session list lock must be held during this function to guarantee
@@ -1009,7 +1010,16 @@ void delete_ust_app(struct ust_app *app)
                free(app->event_notifier_group.object);
        }
 
+       event_notifier_write_fd_is_open = lttng_pipe_is_write_open(
+                       app->event_notifier_group.event_pipe);
        lttng_pipe_destroy(app->event_notifier_group.event_pipe);
+       /*
+        * Release the file descriptors reserved for the event notifier pipe.
+        * The app could be destroyed before the write end of the pipe could be
+        * passed to the application (and closed). In that case, both file
+        * descriptors must be released.
+        */
+       lttng_fd_put(LTTNG_FD_APPS, event_notifier_write_fd_is_open ? 2 : 1);
 
        /*
         * Wait until we have deleted the application from the sock hash table
@@ -3708,6 +3718,7 @@ error:
  */
 struct ust_app *ust_app_create(struct ust_register_msg *msg, int sock)
 {
+       int ret;
        struct ust_app *lta = NULL;
        struct lttng_pipe *event_notifier_event_source_pipe = NULL;
 
@@ -3726,6 +3737,18 @@ struct ust_app *ust_app_create(struct ust_register_msg *msg, int sock)
                goto error;
        }
 
+       /*
+        * Reserve the two file descriptors of the event source pipe. The write
+        * end will be closed once it is passed to the application, at which
+        * point a single 'put' will be performed.
+        */
+       ret = lttng_fd_get(LTTNG_FD_APPS, 2);
+       if (ret) {
+               ERR("Failed to reserve two file descriptors for the event source pipe while creating a new application instance: app = '%s' (ppid: %d)",
+                               msg->name, (int) msg->ppid);
+               goto error;
+       }
+
        event_notifier_event_source_pipe = lttng_pipe_open(FD_CLOEXEC);
        if (!event_notifier_event_source_pipe) {
                PERROR("Failed to open application event source pipe: '%s' (ppid = %d)",
@@ -3783,6 +3806,7 @@ struct ust_app *ust_app_create(struct ust_register_msg *msg, int sock)
 
 error_free_pipe:
        lttng_pipe_destroy(event_notifier_event_source_pipe);
+       lttng_fd_put(LTTNG_FD_APPS, 2);
 error:
        return NULL;
 }
@@ -3892,6 +3916,12 @@ int ust_app_setup_event_notifier_group(struct ust_app *app)
                goto error;
        }
 
+       /*
+        * Release the file descriptor that was reserved for the write-end of
+        * the pipe.
+        */
+       lttng_fd_put(LTTNG_FD_APPS, 1);
+
        lttng_ret = notification_thread_command_add_tracer_event_source(
                        notification_thread_handle,
                        lttng_pipe_get_readfd(app->event_notifier_group.event_pipe),