btrfs: move comment in find_parent_nodes()

This comment was much closer to the related code when it was originally
added, but has slowly migrated north far from its ancestral lands.  Move
it back down with its people.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/backref.c

@@ -1204,11 +1204,6 @@ static int find_parent_nodes(struct btrfs_trans_handle *trans,
 	if (time_seq == BTRFS_SEQ_LAST)
 		path->skip_locking = 1;
 
-	/*
-	 * grab both a lock on the path and a lock on the delayed ref head.
-	 * We need both to get a consistent picture of how the refs look
-	 * at a specified point in time
-	 */
 again:
 	head = NULL;
 
@@ -1224,8 +1219,10 @@ static int find_parent_nodes(struct btrfs_trans_handle *trans,
 	if (trans && time_seq != BTRFS_SEQ_LAST) {
 #endif
 		/*
-		 * look if there are updates for this ref queued and lock the
-		 * head
+		 * We have a specific time_seq we care about and trans which
+		 * means we have the path lock, we need to grab the ref head and
+		 * lock it so we have a consistent view of the refs at the given
+		 * time.
 		 */
 		delayed_refs = &trans->transaction->delayed_refs;
 		spin_lock(&delayed_refs->lock);