Commit 5a526eb1 authored Apr 26, 2024 by Zhang Yi

ext4: use reserved metadata blocks when splitting extent on endio

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I9DN5Z


CVE: NA

--------------------------------

ext4 only reserved space for delalloc for data blocks, doesn't reserve
space for metadata blocks in ext4_da_reserve_space(). Besides, if we
enable dioread_nolock mount option, it also doesn't reserve metadata
blocks for the extent status conversion.

In order to prevent data loss caused by fail to allocate metadata blocks
on writeback, we reserve 2% space or 4096 blocks for meta data, and use
EXT4_GET_BLOCKS_PRE_IO to do the potential split in advance. But all
these two methods were just best efforts, if it's really running out of
sapce, there is no difference between splitting extent on writeback and
on IO completed, both will lead to data loss.

The best way is to reserve enough space for metadata. Before that, we
can at least make sure that things won't get worse if we postpone
splitting extent to endio. So let's use reserved sapce in endio too.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>

parent 4f6e49d7

fs/ext4/extents.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -3733,7 +3733,8 @@ static int ext4_convert_unwritten_extents_endio(handle_t *handle,
		(unsigned long long)map->m_lblk, map->m_len);
		#endif
		err = ext4_split_convert_extents(handle, inode, map, ppath,
		EXT4_GET_BLOCKS_CONVERT);
		EXT4_GET_BLOCKS_CONVERT \|
		EXT4_GET_BLOCKS_METADATA_NOFAIL);
		if (err < 0)
		return err;
		path = ext4_find_extent(inode, map->m_lblk, ppath, 0);