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>

1 files changed, 28 insertions, 13 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 6f420c8efdaf..0ec8e228b89f 100644
--- 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 {