Fix RCU-related hangs: incorrect lttng_ht_destroy use

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

diff --git a/src/bin/lttng-sessiond/trace-ust.c b/src/bin/lttng-sessiond/trace-ust.c
index cd8ff1053caa7c6163fe7686288d071e5dedafc0..7592d774177a43abb8782424084c711e371bcc5c 100644 (file)
--- a/src/bin/lttng-sessiond/trace-ust.c
+++ b/src/bin/lttng-sessiond/trace-ust.c
@@ -180,8 +180,7 @@ error:
  *
  * Return pointer to structure or NULL.
  */
-struct ltt_ust_session *trace_ust_create_session(char *path,
-               unsigned int session_id)
+struct ltt_ust_session *trace_ust_create_session(unsigned int session_id)
 {
        struct ltt_ust_session *lus;
 
@@ -224,24 +223,10 @@ struct ltt_ust_session *trace_ust_create_session(char *path,
         */
        lus->tmp_consumer = NULL;
 
-       /* Use the default consumer output which is the tracing session path. */
-       if (*path != '\0') {
-               int ret;
-
-               ret = snprintf(lus->consumer->dst.trace_path, PATH_MAX,
-                               "%s" DEFAULT_UST_TRACE_DIR, path);
-               if (ret < 0) {
-                       PERROR("snprintf UST consumer trace path");
-                       goto error_path;
-               }
-       }
-
        DBG2("UST trace session create successful");
 
        return lus;
 
-error_path:
-       consumer_destroy_output(lus->consumer);
 error_consumer:
        lttng_ht_destroy(lus->domain_global.channels);
        free(lus);
@@ -254,13 +239,11 @@ error:
  *
  * Return pointer to structure or NULL.
  */
-struct ltt_ust_channel *trace_ust_create_channel(struct lttng_channel *chan,
-               char *path)
+struct ltt_ust_channel *trace_ust_create_channel(struct lttng_channel *chan)
 {
        struct ltt_ust_channel *luc;
 
        assert(chan);
-       assert(path);
 
        luc = zmalloc(sizeof(struct ltt_ust_channel));
        if (luc == NULL) {
@@ -491,12 +474,14 @@ static void destroy_contexts(struct lttng_ht *ht)
 
        assert(ht);
 
+       rcu_read_lock();
        cds_lfht_for_each_entry(ht->ht, &iter.iter, node, node) {
                ret = lttng_ht_del(ht, &iter);
                if (!ret) {
                        call_rcu(&node->head, destroy_context_rcu);
                }
        }
+       rcu_read_unlock();
 
        lttng_ht_destroy(ht);
 }
@@ -537,34 +522,34 @@ static void destroy_events(struct lttng_ht *events)
 
        assert(events);
 
+       rcu_read_lock();
        cds_lfht_for_each_entry(events->ht, &iter.iter, node, node) {
                ret = lttng_ht_del(events, &iter);
                assert(!ret);
                call_rcu(&node->head, destroy_event_rcu);
        }
+       rcu_read_unlock();
 
        lttng_ht_destroy(events);
 }
 
 /*
  * Cleanup ust channel structure.
+ *
+ * Should _NOT_ be called with RCU read lock held.
  */
-void trace_ust_destroy_channel(struct ltt_ust_channel *channel)
+static void _trace_ust_destroy_channel(struct ltt_ust_channel *channel)
 {
        assert(channel);
 
        DBG2("Trace destroy UST channel %s", channel->name);
 
-       rcu_read_lock();
-
        /* Destroying all events of the channel */
        destroy_events(channel->events);
        /* Destroying all context of the channel */
        destroy_contexts(channel->ctx);
 
        free(channel);
-
-       rcu_read_unlock();
 }
 
 /*
@@ -577,7 +562,12 @@ static void destroy_channel_rcu(struct rcu_head *head)
        struct ltt_ust_channel *channel =
                caa_container_of(node, struct ltt_ust_channel, node);
 
-       trace_ust_destroy_channel(channel);
+       _trace_ust_destroy_channel(channel);
+}
+
+void trace_ust_destroy_channel(struct ltt_ust_channel *channel)
+{
+       call_rcu(&channel->node.head, destroy_channel_rcu);
 }
 
 /*
@@ -612,10 +602,9 @@ static void destroy_channels(struct lttng_ht *channels)
                assert(!ret);
                call_rcu(&node->head, destroy_channel_rcu);
        }
+       rcu_read_unlock();
 
        lttng_ht_destroy(channels);
-
-       rcu_read_unlock();
 }
 
 /*
@@ -630,6 +619,8 @@ static void destroy_domain_global(struct ltt_ust_domain_global *dom)
 
 /*
  * Cleanup ust session structure
+ *
+ * Should *NOT* be called with RCU read-side lock held.
  */
 void trace_ust_destroy_session(struct ltt_ust_session *session)
 {
@@ -637,8 +628,6 @@ void trace_ust_destroy_session(struct ltt_ust_session *session)
 
        assert(session);
 
-       rcu_read_lock();
-
        DBG2("Trace UST destroy session %u", session->id);
 
        /* Cleaning up UST domain */
@@ -656,6 +645,4 @@ void trace_ust_destroy_session(struct ltt_ust_session *session)
        consumer_destroy_output(session->tmp_consumer);
 
        free(session);
-
-       rcu_read_unlock();
 }