Fix: notification thread: RCU-safe reclaim of hash table nodes

Adapted from master branch commit 83b934ad.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>

diff --git a/src/bin/lttng-sessiond/notification-thread-commands.h b/src/bin/lttng-sessiond/notification-thread-commands.h
index 8885d4faf57d639965b3f5326c50d81a9ba7099d..0aceb177563ec29eb4deef7510f15008593c5f79 100644 (file)
--- a/src/bin/lttng-sessiond/notification-thread-commands.h
+++ b/src/bin/lttng-sessiond/notification-thread-commands.h
@@ -48,6 +48,8 @@ struct channel_info {
        char *channel_name;
        uint64_t capacity;
        struct cds_lfht_node channels_ht_node;
+       /* call_rcu delayed reclaim. */
+       struct rcu_head rcu_node;
 };
 
 struct notification_thread_command {

diff --git a/src/bin/lttng-sessiond/notification-thread-events.c b/src/bin/lttng-sessiond/notification-thread-events.c
index f54141e73b2a14341b1bd1610db5e8400daeb530..4799c718641bfb0be35bf9433405abf71ab82ba4 100644 (file)
--- a/src/bin/lttng-sessiond/notification-thread-events.c
+++ b/src/bin/lttng-sessiond/notification-thread-events.c
@@ -58,11 +58,15 @@ struct lttng_channel_trigger_list {
        struct channel_key channel_key;
        struct cds_list_head list;
        struct cds_lfht_node channel_triggers_ht_node;
+       /* call_rcu delayed reclaim. */
+       struct rcu_head rcu_node;
 };
 
 struct lttng_trigger_ht_element {
        struct lttng_trigger *trigger;
        struct cds_lfht_node node;
+       /* call_rcu delayed reclaim. */
+       struct rcu_head rcu_node;
 };
 
 struct lttng_condition_list_element {
@@ -79,6 +83,8 @@ struct notification_client_list {
        struct lttng_trigger *trigger;
        struct cds_list_head list;
        struct cds_lfht_node notification_trigger_ht_node;
+       /* call_rcu delayed reclaim. */
+       struct rcu_head rcu_node;
 };
 
 struct notification_client {
@@ -145,6 +151,8 @@ struct notification_client {
                        struct lttng_dynamic_buffer buffer;
                } outbound;
        } communication;
+       /* call_rcu delayed reclaim. */
+       struct rcu_head rcu_node;
 };
 
 struct channel_state_sample {
@@ -152,6 +160,8 @@ struct channel_state_sample {
        struct cds_lfht_node channel_state_ht_node;
        uint64_t highest_usage;
        uint64_t lowest_usage;
+       /* call_rcu delayed reclaim. */
+       struct rcu_head rcu_node;
 };
 
 static unsigned long hash_channel_key(struct channel_key *key);
@@ -332,6 +342,12 @@ unsigned long hash_channel_key(struct channel_key *key)
        return key_hash ^ domain_hash;
 }
 
+static
+void free_channel_info_rcu(struct rcu_head *node)
+{
+       free(caa_container_of(node, struct channel_info, rcu_node));
+}
+
 static
 void channel_info_destroy(struct channel_info *channel_info)
 {
@@ -345,7 +361,7 @@ void channel_info_destroy(struct channel_info *channel_info)
        if (channel_info->channel_name) {
                free(channel_info->channel_name);
        }
-       free(channel_info);
+       call_rcu(&channel_info->rcu_node, free_channel_info_rcu);
 }
 
 static
@@ -672,6 +688,12 @@ end:
        return 0;
 }
 
+static
+void free_notification_client_rcu(struct rcu_head *node)
+{
+       free(caa_container_of(node, struct notification_client, rcu_node));
+}
+
 static
 void notification_client_destroy(struct notification_client *client,
                struct notification_thread_state *state)
@@ -694,7 +716,7 @@ void notification_client_destroy(struct notification_client *client,
        }
        lttng_dynamic_buffer_reset(&client->communication.inbound.buffer);
        lttng_dynamic_buffer_reset(&client->communication.outbound.buffer);
-       free(client);
+       call_rcu(&client->rcu_node, free_notification_client_rcu);
 }
 
 /*
@@ -821,6 +843,7 @@ int handle_notification_thread_command_add_channel(
 
        channel_key = &new_channel_info->key;
 
+       rcu_read_lock();
        /* Build a list of all triggers applying to the new channel. */
        cds_lfht_for_each_entry(state->triggers_ht, &iter, trigger_ht_element,
                        node) {
@@ -833,7 +856,7 @@ int handle_notification_thread_command_add_channel(
 
                new_element = zmalloc(sizeof(*new_element));
                if (!new_element) {
-                       goto error;
+                       goto error_unlock;
                }
                CDS_INIT_LIST_HEAD(&new_element->node);
                new_element->trigger = trigger_ht_element->trigger;
@@ -845,14 +868,13 @@ int handle_notification_thread_command_add_channel(
                        trigger_count);
        channel_trigger_list = zmalloc(sizeof(*channel_trigger_list));
        if (!channel_trigger_list) {
-               goto error;
+               goto error_unlock;
        }
        channel_trigger_list->channel_key = *channel_key;
        CDS_INIT_LIST_HEAD(&channel_trigger_list->list);
        cds_lfht_node_init(&channel_trigger_list->channel_triggers_ht_node);
        cds_list_splice(&trigger_list, &channel_trigger_list->list);
 
-       rcu_read_lock();
        /* Add channel to the channel_ht which owns the channel_infos. */
        cds_lfht_add(state->channels_ht,
                        hash_channel_key(channel_key),
@@ -867,12 +889,28 @@ int handle_notification_thread_command_add_channel(
        rcu_read_unlock();
        *cmd_result = LTTNG_OK;
        return 0;
+error_unlock:
+       rcu_read_unlock();
 error:
        /* Empty trigger list */
        channel_info_destroy(new_channel_info);
        return 1;
 }
 
+static
+void free_channel_trigger_list_rcu(struct rcu_head *node)
+{
+       free(caa_container_of(node, struct lttng_channel_trigger_list,
+                       rcu_node));
+}
+
+static
+void free_channel_state_sample_rcu(struct rcu_head *node)
+{
+       free(caa_container_of(node, struct channel_state_sample,
+                       rcu_node));
+}
+
 static
 int handle_notification_thread_command_remove_channel(
        struct notification_thread_state *state,
@@ -915,7 +953,7 @@ int handle_notification_thread_command_remove_channel(
                free(trigger_list_element);
        }
        cds_lfht_del(state->channel_triggers_ht, node);
-       free(trigger_list);
+       call_rcu(&trigger_list->rcu_node, free_channel_trigger_list_rcu);
 
        /* Free sampled channel state. */
        cds_lfht_lookup(state->channel_state_ht,
@@ -934,7 +972,7 @@ int handle_notification_thread_command_remove_channel(
                                channel_state_ht_node);
 
                cds_lfht_del(state->channel_state_ht, node);
-               free(sample);
+               call_rcu(&sample->rcu_node, free_channel_state_sample_rcu);
        }
 
        /* Remove the channel from the channels_ht and free it. */
@@ -1172,6 +1210,20 @@ error:
        return ret;
 }
 
+static
+void free_notification_client_list_rcu(struct rcu_head *node)
+{
+       free(caa_container_of(node, struct notification_client_list,
+                       rcu_node));
+}
+
+static
+void free_lttng_trigger_ht_element_rcu(struct rcu_head *node)
+{
+       free(caa_container_of(node, struct lttng_trigger_ht_element,
+                       rcu_node));
+}
+
 static
 int handle_notification_thread_command_unregister_trigger(
                struct notification_thread_state *state,
@@ -1246,7 +1298,7 @@ int handle_notification_thread_command_unregister_trigger(
                free(client_list_element);
        }
        cds_lfht_del(state->notification_trigger_clients_ht, node);
-       free(client_list);
+       call_rcu(&client_list->rcu_node, free_notification_client_list_rcu);
 
        /* Remove trigger from triggers_ht. */
        trigger_ht_element = caa_container_of(triggers_ht_node,
@@ -1258,7 +1310,7 @@ int handle_notification_thread_command_unregister_trigger(
        action = lttng_trigger_get_action(trigger_ht_element->trigger);
        lttng_action_destroy(action);
        lttng_trigger_destroy(trigger_ht_element->trigger);
-       free(trigger_ht_element);
+       call_rcu(&trigger_ht_element->rcu_node, free_lttng_trigger_ht_element_rcu);
 end:
        rcu_read_unlock();
        if (_cmd_reply) {