Fix RCU-related hangs: incorrect lttng_ht_destroy use

[lttng-tools.git] / src / bin / lttng-sessiond / buffer-registry.c

diff --git a/src/bin/lttng-sessiond/buffer-registry.c b/src/bin/lttng-sessiond/buffer-registry.c
index 5751b8d587f8a1a12a64a1b2fc207aaba22b0534..2df98d7360445b42ae4aba1941cd976d16e6d723 100644 (file)
--- a/src/bin/lttng-sessiond/buffer-registry.c
+++ b/src/bin/lttng-sessiond/buffer-registry.c
@@ -527,8 +527,10 @@ void buffer_reg_channel_destroy(struct buffer_reg_channel *regp,
 
 /*
  * Destroy a buffer registry session with the given domain.
+ *
+ * Should *NOT* be called with RCU read-side lock held.
  */
-void buffer_reg_session_destroy(struct buffer_reg_session *regp,
+static void buffer_reg_session_destroy(struct buffer_reg_session *regp,
                enum lttng_domain_type domain)
 {
        int ret;
@@ -545,9 +547,10 @@ void buffer_reg_session_destroy(struct buffer_reg_session *regp,
                assert(!ret);
                buffer_reg_channel_destroy(reg_chan, domain);
        }
-       lttng_ht_destroy(regp->channels);
        rcu_read_unlock();
 
+       lttng_ht_destroy(regp->channels);
+
        switch (domain) {
        case LTTNG_DOMAIN_UST:
                ust_registry_session_destroy(regp->reg.ust);
@@ -562,8 +565,7 @@ void buffer_reg_session_destroy(struct buffer_reg_session *regp,
 }
 
 /*
- * Remove buffer registry UID object from the global hash table. RCU read side
- * lock MUST be acquired before calling this.
+ * Remove buffer registry UID object from the global hash table.
  */
 void buffer_reg_uid_remove(struct buffer_reg_uid *regp)
 {
@@ -572,9 +574,11 @@ void buffer_reg_uid_remove(struct buffer_reg_uid *regp)
 
        assert(regp);
 
+       rcu_read_lock();
        iter.iter.node = &regp->node.node;
        ret = lttng_ht_del(buffer_registry_uid, &iter);
        assert(!ret);
+       rcu_read_unlock();
 }
 
 static void rcu_free_buffer_reg_uid(struct rcu_head *head)
@@ -620,11 +624,12 @@ void buffer_reg_uid_destroy(struct buffer_reg_uid *regp,
                goto destroy;
        }
 
+       rcu_read_lock();
        /* Get the right socket from the consumer object. */
        socket = consumer_find_socket_by_bitness(regp->bits_per_long,
                        consumer);
        if (!socket) {
-               goto destroy;
+               goto unlock;
        }
 
        switch (regp->domain) {
@@ -637,9 +642,12 @@ void buffer_reg_uid_destroy(struct buffer_reg_uid *regp,
                break;
        default:
                assert(0);
+               rcu_read_unlock();
                return;
        }
 
+unlock:
+       rcu_read_unlock();
 destroy:
        call_rcu(&regp->node.head, rcu_free_buffer_reg_uid);
 }
@@ -679,6 +687,8 @@ void buffer_reg_pid_destroy(struct buffer_reg_pid *regp)
 
 /*
  * Destroy per PID and UID registry hash table.
+ *
+ * Should *NOT* be called with RCU read-side lock held.
  */
 void buffer_reg_destroy_registries(void)
 {