X-Git-Url: https://git.lttng.org/?p=lttng-tools.git;a=blobdiff_plain;f=src%2Fbin%2Flttng-sessiond%2Fust-app.c;h=9a766e4ab68e628cbdec4d9f0432ec0b83dea547;hp=e3995bdf612d0e82a2fea38e0c4008fd4795b8f2;hb=93ec662e687dc15a3601704a1e0c96c51ad228c9;hpb=fb83fe64f250bec7416f18891a8264450c61ead3

diff --git a/src/bin/lttng-sessiond/ust-app.c b/src/bin/lttng-sessiond/ust-app.c
index e3995bdf6..9a766e4ab 100644
--- a/src/bin/lttng-sessiond/ust-app.c
+++ b/src/bin/lttng-sessiond/ust-app.c
@@ -376,6 +376,8 @@ void delete_ust_app_channel_rcu(struct rcu_head *head)
  * 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)
@@ -390,12 +392,22 @@ 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 The session is then unpublished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;
 	}
 
@@ -426,6 +438,8 @@ 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,
@@ -537,7 +551,7 @@ ssize_t ust_app_push_metadata(struct ust_registry_session *registry,
 	char *metadata_str = NULL;
 	size_t len, offset, new_metadata_len_sent;
 	ssize_t ret_val;
-	uint64_t metadata_key;
+	uint64_t metadata_key, metadata_version;
 
 	assert(registry);
 	assert(socket);
@@ -567,6 +581,7 @@ ssize_t ust_app_push_metadata(struct ust_registry_session *registry,
 	offset = registry->metadata_len_sent;
 	len = registry->metadata_len - registry->metadata_len_sent;
 	new_metadata_len_sent = registry->metadata_len;
+	metadata_version = registry->metadata_version;
 	if (len == 0) {
 		DBG3("No metadata to push for metadata key %" PRIu64,
 				registry->metadata_key);
@@ -603,7 +618,7 @@ push_data:
 	 * different bidirectionnal communication sockets.
 	 */
 	ret = consumer_push_metadata(socket, metadata_key,
-			metadata_str, len, offset);
+			metadata_str, len, offset, metadata_version);
 	pthread_mutex_lock(&registry->lock);
 	if (ret < 0) {
 		/*
@@ -787,6 +802,8 @@ void delete_ust_app_session_rcu(struct rcu_head *head)
 /*
  * 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,
@@ -870,6 +887,11 @@ void delete_ust_app(struct ust_app *app)
 	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;
@@ -908,6 +930,7 @@ void delete_ust_app(struct ust_app *app)
 
 	DBG2("UST app pid %d deleted", app->pid);
 	free(app);
+	session_unlock_list();
 }
 
 /*
@@ -928,6 +951,8 @@ void delete_ust_app_rcu(struct rcu_head *head)
 /*
  * 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)
@@ -5955,7 +5980,7 @@ int ust_app_pid_get_channel_runtime_stats(struct ltt_ust_session *usess,
 		}
 
 		/* Get channel */
-		lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &uiter);
+		lttng_ht_lookup(ua_sess->channels, (void *) uchan->name, &uiter);
 		ua_chan_node = lttng_ht_iter_get_node_str(&uiter);
 		/* If the session is found for the app, the channel must be there */
 		assert(ua_chan_node);
@@ -5971,7 +5996,6 @@ int ust_app_pid_get_channel_runtime_stats(struct ltt_ust_session *usess,
 					ua_chan->key, consumer, discarded);
 			goto end;
 		}
-		goto end;
 	}
 
 end: