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c30ad76)
The "record_error" operation is executed concurrently with setting the
error counter in the notifier group without locking, so we need to
explicitly provide existance guarantees.
The only visible transition is from NULL -> !NULL, because the only
situation reverting the error counter back to NULL is on destruction of
the notification group, after an RCU synchronisation guarantees that no
record_error can observe this pointer anymore.
Use the stronger "cmm_smp_mb()" to provide store-release/load-acquire
semantics because the explicit store-release and load-acquire are not
implemented in the CMM model yet.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I3bbeecc00ff33c5d8ad1e3fd41c8a0dc866f1943
{
struct lttng_event_notifier_group *event_notifier_group =
event_notifier->group;
{
struct lttng_event_notifier_group *event_notifier_group =
event_notifier->group;
+ struct lttng_counter *error_counter;
size_t dimension_index[1];
int ret;
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. */
/* This group may not have an error counter attached to it. */
- if (!event_notifier_group->error_counter)
return;
dimension_index[0] = event_notifier->error_counter_index;
ret = event_notifier_group->error_counter->ops->counter_add(
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);
}
if (ret)
WARN_ON_ONCE(1);
}
- event_notifier_group->error_counter = counter;
event_notifier_group->error_counter_len = counter_len;
event_notifier_group->error_counter_len = counter_len;
+ /*
+ * store-release to publish error counter matches load-acquire
+ * in record_error. Ensures the counter is created and the
+ * error_counter_len is set before they are used.
+ * Currently a full memory barrier is used, which could be
+ * turned into acquire-release barriers.
+ */
+ cmm_smp_mb();
+ CMM_STORE_SHARED(event_notifier_group->error_counter, counter);
counter->objd = counter_objd;
counter->event_notifier_group = event_notifier_group; /* owner */
counter->objd = counter_objd;
counter->event_notifier_group = event_notifier_group; /* owner */