Fix: notifier: use store-release/load-acquire for error counter

[lttng-ust.git] / liblttng-ust / event-notifier-notification.c

diff --git a/liblttng-ust/event-notifier-notification.c b/liblttng-ust/event-notifier-notification.c
index 5f7d9d58f24b67bf04fb4cf5fef6b2e8854f8895..ed2c8d28ae217823acace539b5d3e9c777d816c6 100644 (file)
--- a/liblttng-ust/event-notifier-notification.c
+++ b/liblttng-ust/event-notifier-notification.c
@@ -284,17 +284,26 @@ static void record_error(struct lttng_event_notifier *event_notifier)
 {
        struct lttng_event_notifier_group *event_notifier_group =
                        event_notifier->group;
+       struct lttng_counter *error_counter;
        size_t dimension_index[1];
        int ret;
 
+       error_counter = CMM_LOAD_SHARED(event_notifier_group->error_counter);
+       /*
+        * load-acquire paired with store-release orders creation of the
+        * error counter and setting error_counter_len before the
+        * error_counter is used.
+        * Currently a full memory barrier is used, which could be
+        * turned into acquire-release barriers.
+        */
+       cmm_smp_mb();
        /* This group may not have an error counter attached to it. */
-       if (!event_notifier_group->error_counter)
+       if (!error_counter)
                return;
 
        dimension_index[0] = event_notifier->error_counter_index;
        ret = event_notifier_group->error_counter->ops->counter_add(
-                       event_notifier_group->error_counter->counter,
-                       dimension_index, 1);
+                       error_counter->counter, dimension_index, 1);
        if (ret)
                WARN_ON_ONCE(1);
 }