* Extract the lost packet or discarded events counter when the channel is
* being deleted and store the value in the parent channel so we can
* access it from lttng list and at stop/destroy.
+ *
+ * The session list lock must be held by the caller.
*/
static
void save_per_pid_lost_discarded_counters(struct ust_app_channel *ua_chan)
rcu_read_lock();
session = session_find_by_id(ua_chan->session->tracing_id);
- if (!session) {
- ERR("Missing LTT session to get discarded events");
- goto end;
- }
- if (!session->ust_session) {
- ERR("Missing UST session to get discarded events");
+ if (!session || !session->ust_session) {
+ /*
+ * Not finding the session is not an error because there are
+ * multiple ways the channels can be torn down.
+ *
+ * 1) The session daemon can initiate the destruction of the
+ * ust app session after receiving a destroy command or
+ * during its shutdown/teardown.
+ * 2) The application, since we are in per-pid tracing, is
+ * unregistering and tearing down its ust app session.
+ *
+ * Both paths are protected by the session list lock which
+ * ensures that the accounting of lost packets and discarded
+ * events is done exactly once. The session is then unpublished
+ * from the session list, resulting in this condition.
+ */
goto end;
}
/*
* Delete ust app channel safely. RCU read lock must be held before calling
* this function.
+ *
+ * The session list lock must be held by the caller.
*/
static
void delete_ust_app_channel(int sock, struct ust_app_channel *ua_chan,
/*
* Delete ust app session safely. RCU read lock must be held before calling
* this function.
+ *
+ * The session list lock must be held by the caller.
*/
static
void delete_ust_app_session(int sock, struct ust_app_session *ua_sess,
int ret, sock;
struct ust_app_session *ua_sess, *tmp_ua_sess;
+ /*
+ * The session list lock must be held during this function to guarantee
+ * the existence of ua_sess.
+ */
+ session_lock_list();
/* Delete ust app sessions info */
sock = app->sock;
app->sock = -1;
DBG2("UST app pid %d deleted", app->pid);
free(app);
+ session_unlock_list();
}
/*
/*
* Delete the session from the application ht and delete the data structure by
* freeing every object inside and releasing them.
+ *
+ * The session list lock must be held by the caller.
*/
static void destroy_app_session(struct ust_app *app,
struct ust_app_session *ua_sess)
ua_chan->key, consumer, discarded);
goto end;
}
- goto end;
}
end: