@@ -89,6 +89,12 @@ int btrfs_defrag_leaves(struct btrfs_trans_handle *trans,
goto out;
}
btrfs_release_path(path);
+ /*
+ * We don't need a lock on a leaf. btrfs_realloc_node() will lock all
+ * leafs from path->nodes[1], so set lowest_level to 1 to avoid later
+ * a deadlock (attempting to write lock an already write locked leaf).
+ */
+ path->lowest_level = 1;
wret = btrfs_search_slot(trans, root, &key, path, 0, 1);
if (wret < 0) {
@@ -99,9 +105,12 @@ int btrfs_defrag_leaves(struct btrfs_trans_handle *trans,
ret = 0;
goto out;
}
- path->slots[1] = btrfs_header_nritems(path->nodes[1]);
- next_key_ret = btrfs_find_next_key(root, path, &key, 1,
- min_trans);
+ /*
+ * The node at level 1 must always be locked when our path has
+ * keep_locks set and lowest_level is 1, regardless of the value of
+ * path->slots[1].
+ */
+ BUG_ON(path->locks[1] == 0);
ret = btrfs_realloc_node(trans, root,
path->nodes[1], 0,
&last_ret,
@@ -110,6 +119,18 @@ int btrfs_defrag_leaves(struct btrfs_trans_handle *trans,
WARN_ON(ret == -EAGAIN);
goto out;
}
+ /*
+ * Now that we reallocated the node we can find the next key. Note that
+ * btrfs_find_next_key() can release our path and do another search
+ * without COWing, this is because even with path->keep_locks = 1,
+ * btrfs_search_slot() / ctree.c:unlock_up() does not keeps a lock on a
+ * node when path->slots[node_level - 1] does not point to the last
+ * item or a slot beyond the last item (ctree.c:unlock_up()). Therefore
+ * we search for the next key after reallocating our node.
+ */
+ path->slots[1] = btrfs_header_nritems(path->nodes[1]);
+ next_key_ret = btrfs_find_next_key(root, path, &key, 1,
+ min_trans);
if (next_key_ret == 0) {
memcpy(&root->defrag_progress, &key, sizeof(key));
ret = -EAGAIN;