Fix: deadlock between UST registry lock and consumer lock

[lttng-tools.git] / src / bin / lttng-sessiond / ust-registry.h

diff --git a/src/bin/lttng-sessiond/ust-registry.h b/src/bin/lttng-sessiond/ust-registry.h
index f195b7447b4122c8792ffa0302ffc3418349ab49..0cba8a334e54609df98d5e615662d68a73654c70 100644 (file)
--- a/src/bin/lttng-sessiond/ust-registry.h
+++ b/src/bin/lttng-sessiond/ust-registry.h
@@ -33,8 +33,12 @@ struct ust_app;
 
 struct ust_registry_session {
        /*
-        * With multiple writers and readers, use this lock to access the registry.
-        * Can nest within the ust app session lock.
+        * With multiple writers and readers, use this lock to access
+        * the registry. Can nest within the ust app session lock.
+        * Also acts as a registry serialization lock. Used by registry
+        * readers to serialize the registry information sent from the
+        * sessiond to the consumerd.
+        * The consumer socket lock nests within this lock.
         */
        pthread_mutex_t lock;
        /* Next channel ID available for a newly registered channel. */
@@ -63,11 +67,13 @@ struct ust_registry_session {
        /* Length of bytes sent to the consumer. */
        size_t metadata_len_sent;
        /*
-        * Hash table containing channels sent by the UST tracer. MUST be accessed
-        * with a RCU read side lock acquired.
+        * Hash table containing channels sent by the UST tracer. MUST
+        * be accessed with a RCU read side lock acquired.
         */
        struct lttng_ht *channels;
-       /* Unique key to identify the metadata on the consumer side. */
+       /*
+        * Unique key to identify the metadata on the consumer side.
+        */
        uint64_t metadata_key;
        /*
         * Indicates if the metadata is closed on the consumer side. This is to