btrfs: don't BUG_ON btrfs_alloc_path() errors

This patch fixes many callers of btrfs_alloc_path() which BUG_ON allocation
failure. All the sites that are fixed in this patch were checked by me to
be fairly trivial to fix because of at least one of two criteria:

 - Callers of the function catch errors from it already so bubbling the
   error up will be handled.
 - Callers of the function might BUG_ON any nonzero return code in which
   case there is no behavior changed (but we still got to remove a BUG_ON)

The following functions were updated:

btrfs_lookup_extent, alloc_reserved_tree_block, btrfs_remove_block_group,
btrfs_lookup_csums_range, btrfs_csum_file_blocks, btrfs_mark_extent_written,
btrfs_inode_by_name, btrfs_new_inode, btrfs_symlink,
insert_reserved_file_extent, and run_delalloc_nocow
Signed-off-by: Mark Fasheh <mfasheh@suse.com>

fs/btrfs/extent-tree.c

@@ -667,7 +667,9 @@ int btrfs_lookup_extent(struct btrfs_root *root, u64 start, u64 len)
 	struct btrfs_path *path;
 
 	path = btrfs_alloc_path();
-	BUG_ON(!path);
+	if (!path)
+		return -ENOMEM;
+
 	key.objectid = start;
 	key.offset = len;
 	btrfs_set_key_type(&key, BTRFS_EXTENT_ITEM_KEY);
@@ -5494,7 +5496,8 @@ static int alloc_reserved_tree_block(struct btrfs_trans_handle *trans,
 	u32 size = sizeof(*extent_item) + sizeof(*block_info) + sizeof(*iref);
 
 	path = btrfs_alloc_path();
-	BUG_ON(!path);
+	if (!path)
+		return -ENOMEM;
 
 	path->leave_spinning = 1;
 	ret = btrfs_insert_empty_item(trans, fs_info->extent_root, path,
@@ -7162,7 +7165,10 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
 	spin_unlock(&cluster->refill_lock);
 
 	path = btrfs_alloc_path();
-	BUG_ON(!path);
+	if (!path) {
+		ret = -ENOMEM;
+		goto out;
+	}
 
 	inode = lookup_free_space_inode(root, block_group, path);
 	if (!IS_ERR(inode)) {

fs/btrfs/file-item.c

@@ -282,7 +282,8 @@ int btrfs_lookup_csums_range(struct btrfs_root *root, u64 start, u64 end,
 	u16 csum_size = btrfs_super_csum_size(&root->fs_info->super_copy);
 
 	path = btrfs_alloc_path();
-	BUG_ON(!path);
+	if (!path)
+		return -ENOMEM;
 
 	if (search_commit) {
 		path->skip_locking = 1;
@@ -672,7 +673,9 @@ int btrfs_csum_file_blocks(struct btrfs_trans_handle *trans,
 		btrfs_super_csum_size(&root->fs_info->super_copy);
 
 	path = btrfs_alloc_path();
-	BUG_ON(!path);
+	if (!path)
+		return -ENOMEM;
+
 	sector_sum = sums->sums;
 again:
 	next_offset = (u64)-1;

fs/btrfs/file.c

@@ -855,7 +855,8 @@ int btrfs_mark_extent_written(struct btrfs_trans_handle *trans,
 	btrfs_drop_extent_cache(inode, start, end - 1, 0);
 
 	path = btrfs_alloc_path();
-	BUG_ON(!path);
+	if (!path)
+		return -ENOMEM;
 again:
 	recow = 0;
 	split = start;

fs/btrfs/inode.c

@@ -1070,7 +1070,8 @@ static noinline int run_delalloc_nocow(struct inode *inode,
 	u64 ino = btrfs_ino(inode);
 
 	path = btrfs_alloc_path();
-	BUG_ON(!path);
+	if (!path)
+		return -ENOMEM;
 
 	nolock = is_free_space_inode(root, inode);
 
@@ -1644,7 +1645,8 @@ static int insert_reserved_file_extent(struct btrfs_trans_handle *trans,
 	int ret;
 
 	path = btrfs_alloc_path();
-	BUG_ON(!path);
+	if (!path)
+		return -ENOMEM;
 
 	path->leave_spinning = 1;
 
@@ -3713,7 +3715,8 @@ static int btrfs_inode_by_name(struct inode *dir, struct dentry *dentry,
 	int ret = 0;
 
 	path = btrfs_alloc_path();
-	BUG_ON(!path);
+	if (!path)
+		return -ENOMEM;
 
 	di = btrfs_lookup_dir_item(NULL, root, path, btrfs_ino(dir), name,
 				    namelen, 0);
@@ -4438,7 +4441,8 @@ static struct inode *btrfs_new_inode(struct btrfs_trans_handle *trans,
 	int owner;
 
 	path = btrfs_alloc_path();
-	BUG_ON(!path);
+	if (!path)
+		return ERR_PTR(-ENOMEM);
 
 	inode = new_inode(root->fs_info->sb);
 	if (!inode) {
@@ -7194,7 +7198,11 @@ static int btrfs_symlink(struct inode *dir, struct dentry *dentry,
 		goto out_unlock;
 
 	path = btrfs_alloc_path();
-	BUG_ON(!path);
+	if (!path) {
+		err = -ENOMEM;
+		drop_inode = 1;
+		goto out_unlock;
+	}
 	key.objectid = btrfs_ino(inode);
 	key.offset = 0;
 	btrfs_set_key_type(&key, BTRFS_EXTENT_DATA_KEY);