Use default value for metadata file name
[lttng-tools.git] / src / bin / lttng-sessiond / ust-app.c
index c81f6e8f5597e1531292cfee2e4f5b5f57faf0dd..f46183bd36da99afabc8dbd66eea619539f59e24 100644 (file)
@@ -155,7 +155,7 @@ void delete_ust_app_event(int sock, struct ust_app_event *ua_event)
  * this function.
  */
 static
-void delete_ust_app_stream(int sock, struct ltt_ust_stream *stream)
+void delete_ust_app_stream(int sock, struct ust_app_stream *stream)
 {
        if (stream->obj) {
                ustctl_release_object(sock, stream->obj);
@@ -176,7 +176,7 @@ void delete_ust_app_channel(int sock, struct ust_app_channel *ua_chan)
        struct lttng_ht_iter iter;
        struct ust_app_event *ua_event;
        struct ust_app_ctx *ua_ctx;
-       struct ltt_ust_stream *stream, *stmp;
+       struct ust_app_stream *stream, *stmp;
 
        /* Wipe stream */
        cds_list_for_each_entry_safe(stream, stmp, &ua_chan->streams.head, list) {
@@ -256,8 +256,7 @@ static
 void delete_ust_app(struct ust_app *app)
 {
        int ret, sock;
-       struct lttng_ht_iter iter;
-       struct ust_app_session *ua_sess;
+       struct ust_app_session *ua_sess, *tmp_ua_sess;
 
        rcu_read_lock();
 
@@ -265,14 +264,14 @@ void delete_ust_app(struct ust_app *app)
        sock = app->sock;
        app->sock = -1;
 
+       lttng_ht_destroy(app->sessions);
+
        /* Wipe sessions */
-       cds_lfht_for_each_entry(app->sessions->ht, &iter.iter, ua_sess,
-                       node.node) {
-               ret = lttng_ht_del(app->sessions, &iter);
-               assert(!ret);
-               delete_ust_app_session(app->sock, ua_sess);
+       cds_list_for_each_entry_safe(ua_sess, tmp_ua_sess, &app->teardown_head,
+                       teardown_node) {
+               /* Free every object in the session and the session. */
+               delete_ust_app_session(sock, ua_sess);
        }
-       lttng_ht_destroy(app->sessions);
 
        /*
         * Wait until we have deleted the application from the sock hash table
@@ -368,7 +367,13 @@ struct ust_app_channel *alloc_ust_app_channel(char *name,
 
        /* Copy attributes */
        if (attr) {
-               memcpy(&ua_chan->attr, attr, sizeof(ua_chan->attr));
+               /* Translate from lttng_ust_channel to lttng_ust_channel_attr.*/
+               ua_chan->attr.subbuf_size = attr->subbuf_size;
+               ua_chan->attr.num_subbuf = attr->num_subbuf;
+               ua_chan->attr.overwrite = attr->overwrite;
+               ua_chan->attr.switch_timer_interval = attr->switch_timer_interval;
+               ua_chan->attr.read_timer_interval = attr->read_timer_interval;
+               ua_chan->attr.output = attr->output;
        }
 
        DBG3("UST app channel %s allocated", ua_chan->name);
@@ -379,6 +384,28 @@ error:
        return NULL;
 }
 
+/*
+ * Allocate and initialize a UST app stream.
+ *
+ * Return newly allocated stream pointer or NULL on error.
+ */
+static struct ust_app_stream *alloc_ust_app_stream(void)
+{
+       struct ust_app_stream *stream = NULL;
+
+       stream = zmalloc(sizeof(*stream));
+       if (stream == NULL) {
+               PERROR("zmalloc ust app stream");
+               goto error;
+       }
+
+       /* Zero could be a valid value for a handle so flag it to -1. */
+       stream->handle = -1;
+
+error:
+       return stream;
+}
+
 /*
  * Alloc new UST app event.
  */
@@ -722,9 +749,9 @@ error:
 }
 
 /*
- * Create stream onto the UST tracer for a UST session.
+ * Create metadata stream onto the UST tracer for a given session.
  */
-static int create_ust_stream(struct ust_app *app,
+static int create_ust_metadata_stream(struct ust_app *app,
                struct ust_app_session *ua_sess)
 {
        int ret;
@@ -740,6 +767,7 @@ static int create_ust_stream(struct ust_app *app,
        ret = ustctl_create_stream(app->sock, ua_sess->metadata->obj,
                        &ua_sess->metadata->stream_obj);
        if (ret < 0) {
+               lttng_fd_put(LTTNG_FD_APPS, 2);
                ERR("UST create metadata stream failed");
                goto error;
        }
@@ -749,6 +777,66 @@ error:
        return ret;
 }
 
+/*
+ * Create stream onto the UST tracer for a given channel.
+ *
+ * Return -ENOENT if no more stream is available for this channel.
+ * On success, return 0.
+ * On error, return a negative value.
+ */
+static int create_ust_stream(struct ust_app *app,
+               struct ust_app_channel *ua_chan, struct ust_app_stream *stream)
+{
+       int ret;
+
+       assert(app);
+       assert(ua_chan);
+       assert(ua_chan->obj);
+       assert(stream);
+
+       health_code_update(&health_thread_cmd);
+
+       /* We are going to receive 2 fds, we need to reserve them. */
+       ret = lttng_fd_get(LTTNG_FD_APPS, 2);
+       if (ret < 0) {
+               ERR("Exhausted number of available FD on stream creation");
+               /* Just to make sure we never return -ENOENT. */
+               ret = -1;
+               goto error;
+       }
+
+       /*
+        * Set the stream name before creating it. On error, we don't have to
+        * delete it on the tracer side.
+        */
+       ret = snprintf(stream->name, sizeof(stream->name), "%s_%u",
+                       ua_chan->name, ua_chan->streams.count);
+       if (ret < 0) {
+               /* Without the stream name we can't continue using it. */
+               PERROR("snprintf UST create stream");
+               /* Just to make sure we never return -ENOENT. */
+               ret = -1;
+               goto error;
+       }
+
+       ret = ustctl_create_stream(app->sock, ua_chan->obj, &stream->obj);
+       if (ret < 0) {
+               lttng_fd_put(LTTNG_FD_APPS, 2);
+               /* Indicates that there is no more stream for that channel. */
+               if (ret != -LTTNG_UST_ERR_NOENT) {
+                       ERR("UST create metadata stream failed (ret: %d)", ret);
+               }
+               goto error;
+       }
+
+       /* Set stream handle with the returned value. */
+       stream->handle = stream->obj->handle;
+
+error:
+       health_code_update(&health_thread_cmd);
+       return ret;
+}
+
 /*
  * Create the specified channel onto the UST tracer for a UST session.
  */
@@ -759,8 +847,6 @@ static int create_ust_channel(struct ust_app *app,
 
        health_code_update(&health_thread_cmd);
 
-       /* TODO: remove cast and use lttng-ust-abi.h */
-
        /* We are going to receive 2 fds, we need to reserve them. */
        ret = lttng_fd_get(LTTNG_FD_APPS, 2);
        if (ret < 0) {
@@ -770,8 +856,8 @@ static int create_ust_channel(struct ust_app *app,
 
        health_code_update(&health_thread_cmd);
 
-       ret = ustctl_create_channel(app->sock, ua_sess->handle,
-                       (struct lttng_ust_channel_attr *)&ua_chan->attr, &ua_chan->obj);
+       ret = ustctl_create_channel(app->sock, ua_sess->handle, &ua_chan->attr,
+                       &ua_chan->obj);
        if (ret < 0) {
                ERR("Creating channel %s for app (pid: %d, sock: %d) "
                                "and session handle %d with ret %d",
@@ -1031,17 +1117,27 @@ error:
 }
 
 /*
- * Create a UST session onto the tracer of app and add it the session
- * hashtable.
+ * Create a session on the tracer side for the given app.
  *
- * Return ust app session or NULL on error.
+ * On success, ua_sess_ptr is populated with the session pointer or else left
+ * untouched. If the session was created, is_created is set to 1. On error,
+ * it's left untouched. Note that ua_sess_ptr is mandatory but is_created can
+ * be NULL.
+ *
+ * Returns 0 on success or else a negative code which is either -ENOMEM or
+ * -ENOTCONN which is the default code if the ustctl_create_session fails.
  */
-static struct ust_app_session *create_ust_app_session(
-               struct ltt_ust_session *usess, struct ust_app *app)
+static int create_ust_app_session(struct ltt_ust_session *usess,
+               struct ust_app *app, struct ust_app_session **ua_sess_ptr,
+               int *is_created)
 {
-       int ret;
+       int ret, created = 0;
        struct ust_app_session *ua_sess;
 
+       assert(usess);
+       assert(app);
+       assert(ua_sess_ptr);
+
        health_code_update(&health_thread_cmd);
 
        ua_sess = lookup_session_by_app(usess, app);
@@ -1051,9 +1147,11 @@ static struct ust_app_session *create_ust_app_session(
                ua_sess = alloc_ust_app_session();
                if (ua_sess == NULL) {
                        /* Only malloc can failed so something is really wrong */
-                       goto end;
+                       ret = -ENOMEM;
+                       goto error;
                }
                shadow_copy_session(ua_sess, usess, app);
+               created = 1;
        }
 
        health_code_update(&health_thread_cmd);
@@ -1063,9 +1161,14 @@ static struct ust_app_session *create_ust_app_session(
                if (ret < 0) {
                        ERR("Creating session for app pid %d", app->pid);
                        delete_ust_app_session(-1, ua_sess);
-                       /* This means that the tracer is gone... */
-                       ua_sess = (void*) -1UL;
-                       goto end;
+                       if (ret != -ENOMEM) {
+                               /*
+                                * Tracer is probably gone or got an internal error so let's
+                                * behave like it will soon unregister or not usable.
+                                */
+                               ret = -ENOTCONN;
+                       }
+                       goto error;
                }
 
                ua_sess->handle = ret;
@@ -1077,9 +1180,16 @@ static struct ust_app_session *create_ust_app_session(
                DBG2("UST app session created successfully with handle %d", ret);
        }
 
-end:
+       *ua_sess_ptr = ua_sess;
+       if (is_created) {
+               *is_created = created;
+       }
+       /* Everything went well. */
+       ret = 0;
+
+error:
        health_code_update(&health_thread_cmd);
-       return ua_sess;
+       return ret;
 }
 
 /*
@@ -1213,11 +1323,12 @@ error:
 }
 
 /*
- * Create UST app channel and create it on the tracer.
+ * Create UST app channel and create it on the tracer. Set ua_chanp of the
+ * newly created channel if not NULL.
  */
-static struct ust_app_channel *create_ust_app_channel(
-               struct ust_app_session *ua_sess, struct ltt_ust_channel *uchan,
-               struct ust_app *app)
+static int create_ust_app_channel(struct ust_app_session *ua_sess,
+               struct ltt_ust_channel *uchan, struct ust_app *app,
+               struct ust_app_channel **ua_chanp)
 {
        int ret = 0;
        struct lttng_ht_iter iter;
@@ -1235,6 +1346,7 @@ static struct ust_app_channel *create_ust_app_channel(
        ua_chan = alloc_ust_app_channel(uchan->name, &uchan->attr);
        if (ua_chan == NULL) {
                /* Only malloc can fail here */
+               ret = -ENOMEM;
                goto error;
        }
        shadow_copy_channel(ua_chan, uchan);
@@ -1246,17 +1358,23 @@ static struct ust_app_channel *create_ust_app_channel(
                goto error;
        }
 
+       /* Only add the channel if successful on the tracer side. */
        lttng_ht_add_unique_str(ua_sess->channels, &ua_chan->node);
 
        DBG2("UST app create channel %s for PID %d completed", ua_chan->name,
                        app->pid);
 
 end:
-       return ua_chan;
+       if (ua_chanp) {
+               *ua_chanp = ua_chan;
+       }
+
+       /* Everything went well. */
+       return 0;
 
 error:
        delete_ust_app_channel(-1, ua_chan);
-       return NULL;
+       return ret;
 }
 
 /*
@@ -1344,13 +1462,13 @@ static int create_ust_app_metadata(struct ust_app_session *ua_sess,
 
        /* Open UST metadata stream */
        if (ua_sess->metadata->stream_obj == NULL) {
-               ret = create_ust_stream(app, ua_sess);
+               ret = create_ust_metadata_stream(app, ua_sess);
                if (ret < 0) {
                        goto error;
                }
 
                ret = snprintf(ua_sess->metadata->pathname, PATH_MAX,
-                               "%s/metadata", ua_sess->path);
+                               "%s/" DEFAULT_METADATA_NAME, ua_sess->path);
                if (ret < 0) {
                        PERROR("asprintf UST create stream");
                        goto error;
@@ -1462,6 +1580,8 @@ int ust_app_register(struct ust_register_msg *msg, int sock)
        lta->sock = sock;
        lttng_ht_node_init_ulong(&lta->sock_n, (unsigned long)lta->sock);
 
+       CDS_INIT_LIST_HEAD(&lta->teardown_head);
+
        rcu_read_lock();
 
        /*
@@ -1497,6 +1617,7 @@ void ust_app_unregister(int sock)
        struct ust_app *lta;
        struct lttng_ht_node_ulong *node;
        struct lttng_ht_iter iter;
+       struct ust_app_session *ua_sess;
        int ret;
 
        rcu_read_lock();
@@ -1531,6 +1652,22 @@ void ust_app_unregister(int sock)
                                lta->pid);
        }
 
+       /* Remove sessions so they are not visible during deletion.*/
+       cds_lfht_for_each_entry(lta->sessions->ht, &iter.iter, ua_sess,
+                       node.node) {
+               ret = lttng_ht_del(lta->sessions, &iter);
+               if (ret) {
+                       /* The session was already removed so scheduled for teardown. */
+                       continue;
+               }
+
+               /*
+                * Add session to list for teardown. This is safe since at this point we
+                * are the only one using this list.
+                */
+               cds_list_add(&ua_sess->teardown_node, &lta->teardown_head);
+       }
+
        /* Free memory */
        call_rcu(&lta->pid_n.head, delete_ust_app_rcu);
 
@@ -1562,11 +1699,11 @@ int ust_app_list_events(struct lttng_event **events)
        size_t nbmem, count = 0;
        struct lttng_ht_iter iter;
        struct ust_app *app;
-       struct lttng_event *tmp;
+       struct lttng_event *tmp_event;
 
        nbmem = UST_APP_EVENT_LIST_SIZE;
-       tmp = zmalloc(nbmem * sizeof(struct lttng_event));
-       if (tmp == NULL) {
+       tmp_event = zmalloc(nbmem * sizeof(struct lttng_event));
+       if (tmp_event == NULL) {
                PERROR("zmalloc ust app events");
                ret = -ENOMEM;
                goto error;
@@ -1598,29 +1735,31 @@ int ust_app_list_events(struct lttng_event **events)
                        health_code_update(&health_thread_cmd);
                        if (count >= nbmem) {
                                /* In case the realloc fails, we free the memory */
-                               void *tmp_ptr = (void *) tmp;
+                               void *ptr;
+
                                DBG2("Reallocating event list from %zu to %zu entries", nbmem,
                                                2 * nbmem);
                                nbmem *= 2;
-                               tmp = realloc(tmp, nbmem * sizeof(struct lttng_event));
-                               if (tmp == NULL) {
+                               ptr = realloc(tmp_event, nbmem * sizeof(struct lttng_event));
+                               if (ptr == NULL) {
                                        PERROR("realloc ust app events");
-                                       free(tmp_ptr);
+                                       free(tmp_event);
                                        ret = -ENOMEM;
                                        goto rcu_error;
                                }
+                               tmp_event = ptr;
                        }
-                       memcpy(tmp[count].name, uiter.name, LTTNG_UST_SYM_NAME_LEN);
-                       tmp[count].loglevel = uiter.loglevel;
-                       tmp[count].type = (enum lttng_event_type) LTTNG_UST_TRACEPOINT;
-                       tmp[count].pid = app->pid;
-                       tmp[count].enabled = -1;
+                       memcpy(tmp_event[count].name, uiter.name, LTTNG_UST_SYM_NAME_LEN);
+                       tmp_event[count].loglevel = uiter.loglevel;
+                       tmp_event[count].type = (enum lttng_event_type) LTTNG_UST_TRACEPOINT;
+                       tmp_event[count].pid = app->pid;
+                       tmp_event[count].enabled = -1;
                        count++;
                }
        }
 
        ret = count;
-       *events = tmp;
+       *events = tmp_event;
 
        DBG2("UST app list events done (%zu events)", count);
 
@@ -1640,11 +1779,11 @@ int ust_app_list_event_fields(struct lttng_event_field **fields)
        size_t nbmem, count = 0;
        struct lttng_ht_iter iter;
        struct ust_app *app;
-       struct lttng_event_field *tmp;
+       struct lttng_event_field *tmp_event;
 
        nbmem = UST_APP_EVENT_LIST_SIZE;
-       tmp = zmalloc(nbmem * sizeof(struct lttng_event_field));
-       if (tmp == NULL) {
+       tmp_event = zmalloc(nbmem * sizeof(struct lttng_event_field));
+       if (tmp_event == NULL) {
                PERROR("zmalloc ust app event fields");
                ret = -ENOMEM;
                goto error;
@@ -1676,34 +1815,36 @@ int ust_app_list_event_fields(struct lttng_event_field **fields)
                        health_code_update(&health_thread_cmd);
                        if (count >= nbmem) {
                                /* In case the realloc fails, we free the memory */
-                               void *tmp_ptr = (void *) tmp;
+                               void *ptr;
+
                                DBG2("Reallocating event field list from %zu to %zu entries", nbmem,
                                                2 * nbmem);
                                nbmem *= 2;
-                               tmp = realloc(tmp, nbmem * sizeof(struct lttng_event_field));
-                               if (tmp == NULL) {
+                               ptr = realloc(tmp_event, nbmem * sizeof(struct lttng_event_field));
+                               if (ptr == NULL) {
                                        PERROR("realloc ust app event fields");
-                                       free(tmp_ptr);
+                                       free(tmp_event);
                                        ret = -ENOMEM;
                                        goto rcu_error;
                                }
+                               tmp_event = ptr;
                        }
 
-                       memcpy(tmp[count].field_name, uiter.field_name, LTTNG_UST_SYM_NAME_LEN);
-                       tmp[count].type = uiter.type;
-                       tmp[count].nowrite = uiter.nowrite;
+                       memcpy(tmp_event[count].field_name, uiter.field_name, LTTNG_UST_SYM_NAME_LEN);
+                       tmp_event[count].type = uiter.type;
+                       tmp_event[count].nowrite = uiter.nowrite;
 
-                       memcpy(tmp[count].event.name, uiter.event_name, LTTNG_UST_SYM_NAME_LEN);
-                       tmp[count].event.loglevel = uiter.loglevel;
-                       tmp[count].event.type = LTTNG_UST_TRACEPOINT;
-                       tmp[count].event.pid = app->pid;
-                       tmp[count].event.enabled = -1;
+                       memcpy(tmp_event[count].event.name, uiter.event_name, LTTNG_UST_SYM_NAME_LEN);
+                       tmp_event[count].event.loglevel = uiter.loglevel;
+                       tmp_event[count].event.type = LTTNG_UST_TRACEPOINT;
+                       tmp_event[count].event.pid = app->pid;
+                       tmp_event[count].event.enabled = -1;
                        count++;
                }
        }
 
        ret = count;
-       *fields = tmp;
+       *fields = tmp_event;
 
        DBG2("UST app list event fields done (%zu events)", count);
 
@@ -1964,8 +2105,10 @@ int ust_app_disable_all_event_glb(struct ltt_ust_session *usess,
                        continue;
                }
                ua_sess = lookup_session_by_app(usess, app);
-               /* If ua_sess is NULL, there is a code flow error */
-               assert(ua_sess);
+               if (!ua_sess) {
+                       /* The application has problem or is probably dead. */
+                       continue;
+               }
 
                /* Lookup channel in the ust app session */
                lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &uiter);
@@ -1997,11 +2140,10 @@ int ust_app_disable_all_event_glb(struct ltt_ust_session *usess,
 int ust_app_create_channel_glb(struct ltt_ust_session *usess,
                struct ltt_ust_channel *uchan)
 {
-       int ret = 0;
+       int ret = 0, created;
        struct lttng_ht_iter iter;
        struct ust_app *app;
-       struct ust_app_session *ua_sess;
-       struct ust_app_channel *ua_chan;
+       struct ust_app_session *ua_sess = NULL;
 
        /* Very wrong code flow */
        assert(usess);
@@ -2026,29 +2168,39 @@ int ust_app_create_channel_glb(struct ltt_ust_session *usess,
                 * that if session exist, it will simply return a pointer to the ust
                 * app session.
                 */
-               ua_sess = create_ust_app_session(usess, app);
-               if (ua_sess == NULL) {
-                       /* The malloc() failed. */
-                       ret = -1;
-                       goto error;
-               } else if (ua_sess == (void *) -1UL) {
-                       /* The application's socket is not valid. Contiuing */
-                       ret = -1;
-                       continue;
+               ret = create_ust_app_session(usess, app, &ua_sess, &created);
+               if (ret < 0) {
+                       switch (ret) {
+                       case -ENOTCONN:
+                               /*
+                                * The application's socket is not valid. Either a bad socket
+                                * or a timeout on it. We can't inform the caller that for a
+                                * specific app, the session failed so lets continue here.
+                                */
+                               continue;
+                       case -ENOMEM:
+                       default:
+                               goto error_rcu_unlock;
+                       }
                }
+               assert(ua_sess);
 
-               /* Create channel onto application */
-               ua_chan = create_ust_app_channel(ua_sess, uchan, app);
-               if (ua_chan == NULL) {
-                       /* Major problem here and it's maybe the tracer or malloc() */
-                       ret = -1;
-                       goto error;
+               /* Create channel onto application. We don't need the chan ref. */
+               ret = create_ust_app_channel(ua_sess, uchan, app, NULL);
+               if (ret < 0) {
+                       if (ret == -ENOMEM) {
+                               /* No more memory is a fatal error. Stop right now. */
+                               goto error_rcu_unlock;
+                       }
+                       /* Cleanup the created session if it's the case. */
+                       if (created) {
+                               delete_ust_app_session(app->sock, ua_sess);
+                       }
                }
        }
 
+error_rcu_unlock:
        rcu_read_unlock();
-
-error:
        return ret;
 }
 
@@ -2087,8 +2239,10 @@ int ust_app_enable_event_glb(struct ltt_ust_session *usess,
                        continue;
                }
                ua_sess = lookup_session_by_app(usess, app);
-               /* If ua_sess is NULL, there is a code flow error */
-               assert(ua_sess);
+               if (!ua_sess) {
+                       /* The application has problem or is probably dead. */
+                       continue;
+               }
 
                /* Lookup channel in the ust app session */
                lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &uiter);
@@ -2147,8 +2301,10 @@ int ust_app_create_event_glb(struct ltt_ust_session *usess,
                        continue;
                }
                ua_sess = lookup_session_by_app(usess, app);
-               /* If ua_sess is NULL, there is a code flow error */
-               assert(ua_sess);
+               if (!ua_sess) {
+                       /* The application has problem or is probably dead. */
+                       continue;
+               }
 
                /* Lookup channel in the ust app session */
                lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &uiter);
@@ -2184,7 +2340,7 @@ int ust_app_start_trace(struct ltt_ust_session *usess, struct ust_app *app)
        struct lttng_ht_iter iter;
        struct ust_app_session *ua_sess;
        struct ust_app_channel *ua_chan;
-       struct ltt_ust_stream *ustream;
+       struct ust_app_stream *ustream;
        struct consumer_socket *socket;
 
        DBG("Starting tracing for ust app pid %d", app->pid);
@@ -2197,7 +2353,8 @@ int ust_app_start_trace(struct ltt_ust_session *usess, struct ust_app *app)
 
        ua_sess = lookup_session_by_app(usess, app);
        if (ua_sess == NULL) {
-               goto error_rcu_unlock;
+               /* The session is in teardown process. Ignore and continue. */
+               goto end;
        }
 
        /* Upon restart, we skip the setup, already done */
@@ -2219,9 +2376,6 @@ int ust_app_start_trace(struct ltt_ust_session *usess, struct ust_app *app)
                }
        }
 
-       /* Indicate that the session has been started once */
-       ua_sess->started = 1;
-
        ret = create_ust_app_metadata(ua_sess, usess->pathname, app);
        if (ret < 0) {
                ret = LTTNG_ERR_UST_META_FAIL;
@@ -2234,48 +2388,32 @@ int ust_app_start_trace(struct ltt_ust_session *usess, struct ust_app *app)
                /* Create all streams */
                while (1) {
                        /* Create UST stream */
-                       ustream = zmalloc(sizeof(*ustream));
+                       ustream = alloc_ust_app_stream();
                        if (ustream == NULL) {
-                               PERROR("zmalloc ust stream");
-                               goto error_rcu_unlock;
-                       }
-
-                       /* We are going to receive 2 fds, we need to reserve them. */
-                       ret = lttng_fd_get(LTTNG_FD_APPS, 2);
-                       if (ret < 0) {
-                               ERR("Exhausted number of available FD upon stream create");
-                               free(ustream);
                                goto error_rcu_unlock;
                        }
 
                        health_code_update(&health_thread_cmd);
 
-                       ret = ustctl_create_stream(app->sock, ua_chan->obj,
-                                       &ustream->obj);
+                       ret = create_ust_stream(app, ua_chan, ustream);
                        if (ret < 0) {
-                               /* Got all streams */
-                               lttng_fd_put(LTTNG_FD_APPS, 2);
+                               /* Free unused memory after this point. */
                                free(ustream);
+                               if (ret == -LTTNG_UST_ERR_NOENT) {
+                                       /* Got all streams. Continue normal execution. */
+                                       break;
+                               }
+                               /* Error at this point. Stop everything. */
                                ret = LTTNG_ERR_UST_STREAM_FAIL;
-                               break;
+                               goto error_rcu_unlock;
                        }
-                       ustream->handle = ustream->obj->handle;
 
                        health_code_update(&health_thread_cmd);
 
-                       /* Order is important */
+                       /* Order is important this is why a list is used. */
                        cds_list_add_tail(&ustream->list, &ua_chan->streams.head);
-                       ret = snprintf(ustream->name, sizeof(ustream->name), "%s_%u",
-                                       ua_chan->name, ua_chan->streams.count);
                        ua_chan->streams.count++;
-                       if (ret < 0) {
-                               PERROR("asprintf UST create stream");
-                               /*
-                                * XXX what should we do here with the
-                                * stream ?
-                                */
-                               continue;
-                       }
+
                        DBG2("UST stream %d ready (handle: %d)", ua_chan->streams.count,
                                        ustream->handle);
                }
@@ -2315,10 +2453,13 @@ skip_setup:
        /* This start the UST tracing */
        ret = ustctl_start_session(app->sock, ua_sess->handle);
        if (ret < 0) {
-               ERR("Error starting tracing for app pid: %d", app->pid);
+               ERR("Error starting tracing for app pid: %d (ret: %d)", app->pid, ret);
                goto error_rcu_unlock;
        }
 
+       /* Indicate that the session has been started once */
+       ua_sess->started = 1;
+
        health_code_update(&health_thread_cmd);
 
        /* Quiescent wait after starting trace */
@@ -2355,23 +2496,25 @@ int ust_app_stop_trace(struct ltt_ust_session *usess, struct ust_app *app)
 
        ua_sess = lookup_session_by_app(usess, app);
        if (ua_sess == NULL) {
-               /* Only malloc can failed so something is really wrong */
-               goto error_rcu_unlock;
+               goto end;
        }
 
        /*
         * If started = 0, it means that stop trace has been called for a session
-        * that was never started. This is a code flow error and should never
-        * happen.
+        * that was never started. It's possible since we can have a fail start
+        * from either the application manager thread or the command thread. Simply
+        * indicate that this is a stop error.
         */
-       assert(ua_sess->started == 1);
+       if (!ua_sess->started) {
+               goto error_rcu_unlock;
+       }
 
        health_code_update(&health_thread_cmd);
 
        /* This inhibits UST tracing */
        ret = ustctl_stop_session(app->sock, ua_sess->handle);
        if (ret < 0) {
-               ERR("Error stopping tracing for app pid: %d", app->pid);
+               ERR("Error stopping tracing for app pid: %d (ret: %d)", app->pid, ret);
                goto error_rcu_unlock;
        }
 
@@ -2418,7 +2561,7 @@ error_rcu_unlock:
 /*
  * Destroy a specific UST session in apps.
  */
-int ust_app_destroy_trace(struct ltt_ust_session *usess, struct ust_app *app)
+static int destroy_trace(struct ltt_ust_session *usess, struct ust_app *app)
 {
        struct ust_app_session *ua_sess;
        struct lttng_ust_object_data obj;
@@ -2437,12 +2580,16 @@ int ust_app_destroy_trace(struct ltt_ust_session *usess, struct ust_app *app)
        __lookup_session_by_app(usess, app, &iter);
        node = lttng_ht_iter_get_node_ulong(&iter);
        if (node == NULL) {
-               /* Only malloc can failed so something is really wrong */
-               goto error_rcu_unlock;
+               /* Session is being or is deleted. */
+               goto end;
        }
        ua_sess = caa_container_of(node, struct ust_app_session, node);
        ret = lttng_ht_del(app->sessions, &iter);
-       assert(!ret);
+       if (ret) {
+               /* Already scheduled for teardown. */
+               goto end;
+       }
+
        obj.handle = ua_sess->handle;
        obj.shm_fd = -1;
        obj.wait_fd = -1;
@@ -2460,11 +2607,6 @@ end:
        rcu_read_unlock();
        health_code_update(&health_thread_cmd);
        return 0;
-
-error_rcu_unlock:
-       rcu_read_unlock();
-       health_code_update(&health_thread_cmd);
-       return -1;
 }
 
 /*
@@ -2533,7 +2675,7 @@ int ust_app_destroy_trace_all(struct ltt_ust_session *usess)
        rcu_read_lock();
 
        cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
-               ret = ust_app_destroy_trace(usess, app);
+               ret = destroy_trace(usess, app);
                if (ret < 0) {
                        /* Continue to next apps even on error */
                        continue;
@@ -2553,15 +2695,12 @@ void ust_app_global_update(struct ltt_ust_session *usess, int sock)
        int ret = 0;
        struct lttng_ht_iter iter, uiter, iter_ctx;
        struct ust_app *app;
-       struct ust_app_session *ua_sess;
+       struct ust_app_session *ua_sess = NULL;
        struct ust_app_channel *ua_chan;
        struct ust_app_event *ua_event;
        struct ust_app_ctx *ua_ctx;
 
-       if (usess == NULL) {
-               ERR("No UST session on global update. Returning");
-               goto error;
-       }
+       assert(usess);
 
        DBG2("UST app global update for app sock %d for session id %d", sock,
                        usess->id);
@@ -2578,11 +2717,12 @@ void ust_app_global_update(struct ltt_ust_session *usess, int sock)
                goto error;
        }
 
-       ua_sess = create_ust_app_session(usess, app);
-       if (ua_sess == NULL || ua_sess == (void *) -1UL) {
-               /* Tracer is gone for this session and has been freed */
+       ret = create_ust_app_session(usess, app, &ua_sess, NULL);
+       if (ret < 0) {
+               /* Tracer is probably gone or ENOMEM. */
                goto error;
        }
+       assert(ua_sess);
 
        /*
         * We can iterate safely here over all UST app session sicne the create ust
@@ -2615,12 +2755,6 @@ void ust_app_global_update(struct ltt_ust_session *usess, int sock)
                                /* FIXME: Should we quit here or continue... */
                                continue;
                        }
-
-                       ret = set_ust_event_filter(ua_event, app);
-                       if (ret < 0) {
-                               /* FIXME: Should we quit here or continue... */
-                               continue;
-                       }
                }
        }
 
@@ -2716,8 +2850,10 @@ int ust_app_enable_event_pid(struct ltt_ust_session *usess,
        }
 
        ua_sess = lookup_session_by_app(usess, app);
-       /* If ua_sess is NULL, there is a code flow error */
-       assert(ua_sess);
+       if (!ua_sess) {
+               /* The application has problem or is probably dead. */
+               goto error;
+       }
 
        /* Lookup channel in the ust app session */
        lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &iter);
@@ -2777,8 +2913,10 @@ int ust_app_disable_event_pid(struct ltt_ust_session *usess,
        }
 
        ua_sess = lookup_session_by_app(usess, app);
-       /* If ua_sess is NULL, there is a code flow error */
-       assert(ua_sess);
+       if (!ua_sess) {
+               /* The application has problem or is probably dead. */
+               goto error;
+       }
 
        /* Lookup channel in the ust app session */
        lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &iter);
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