btrfs: handle ENOMEM in btrfs_alloc_tree_block

This is one of the first places to give out when memory is tight. Handle
it properly rather than with a BUG_ON.

Also fix the comment about the return value, which is an ERR_PTR, not
NULL, on error.

Signed-off-by: Omar Sandoval <osandov@osandov.com>
Reviewed-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <clm@fb.com>

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 6f420c8efdaf678597b4c77c8b51f343309d9f88..0ec8e228b89f42505cc0c9c8ffef96e1a2f3f9a4 100644 (file)
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -7546,7 +7546,7 @@ static void unuse_block_rsv(struct btrfs_fs_info *fs_info,
  * returns the key for the extent through ins, and a tree buffer for
  * the first block of the extent through buf.
  *
- * returns the tree buffer or NULL.
+ * returns the tree buffer or an ERR_PTR on error.
  */
 struct extent_buffer *btrfs_alloc_tree_block(struct btrfs_trans_handle *trans,
                                        struct btrfs_root *root,
@@ -7557,6 +7557,7 @@ struct extent_buffer *btrfs_alloc_tree_block(struct btrfs_trans_handle *trans,
        struct btrfs_key ins;
        struct btrfs_block_rsv *block_rsv;
        struct extent_buffer *buf;
+       struct btrfs_delayed_extent_op *extent_op;
        u64 flags = 0;
        int ret;
        u32 blocksize = root->nodesize;
@@ -7577,13 +7578,14 @@ struct extent_buffer *btrfs_alloc_tree_block(struct btrfs_trans_handle *trans,
 
        ret = btrfs_reserve_extent(root, blocksize, blocksize,
                                   empty_size, hint, &ins, 0, 0);
-       if (ret) {
-               unuse_block_rsv(root->fs_info, block_rsv, blocksize);
-               return ERR_PTR(ret);
-       }
+       if (ret)
+               goto out_unuse;
 
        buf = btrfs_init_new_buffer(trans, root, ins.objectid, level);
-       BUG_ON(IS_ERR(buf)); /* -ENOMEM */
+       if (IS_ERR(buf)) {
+               ret = PTR_ERR(buf);
+               goto out_free_reserved;
+       }
 
        if (root_objectid == BTRFS_TREE_RELOC_OBJECTID) {
                if (parent == 0)
@@ -7593,9 +7595,11 @@ struct extent_buffer *btrfs_alloc_tree_block(struct btrfs_trans_handle *trans,
                BUG_ON(parent > 0);
 
        if (root_objectid != BTRFS_TREE_LOG_OBJECTID) {
-               struct btrfs_delayed_extent_op *extent_op;
                extent_op = btrfs_alloc_delayed_extent_op();
-               BUG_ON(!extent_op); /* -ENOMEM */
+               if (!extent_op) {
+                       ret = -ENOMEM;
+                       goto out_free_buf;
+               }
                if (key)
                        memcpy(&extent_op->key, key, sizeof(extent_op->key));
                else
@@ -7610,13 +7614,24 @@ struct extent_buffer *btrfs_alloc_tree_block(struct btrfs_trans_handle *trans,
                extent_op->level = level;
 
                ret = btrfs_add_delayed_tree_ref(root->fs_info, trans,
-                                       ins.objectid,
-                                       ins.offset, parent, root_objectid,
-                                       level, BTRFS_ADD_DELAYED_EXTENT,
-                                       extent_op, 0);
-               BUG_ON(ret); /* -ENOMEM */
+                                                ins.objectid, ins.offset,
+                                                parent, root_objectid, level,
+                                                BTRFS_ADD_DELAYED_EXTENT,
+                                                extent_op, 0);
+               if (ret)
+                       goto out_free_delayed;
        }
        return buf;
+
+out_free_delayed:
+       btrfs_free_delayed_extent_op(extent_op);
+out_free_buf:
+       free_extent_buffer(buf);
+out_free_reserved:
+       btrfs_free_reserved_extent(root, ins.objectid, ins.offset, 0);
+out_unuse:
+       unuse_block_rsv(root->fs_info, block_rsv, blocksize);
+       return ERR_PTR(ret);
 }
 
 struct walk_control {