Re: [PATCH RFC] ext4:record error information when insert extent failed in 'ext4_split_extent_at'

[zhanchengbin <zhanchengbin1@huawei.com>]

There have been a lot of problems here before, but the problem has not 
been fundamentally solved.

On 2022/10/24 20:27, Ye Bin wrote:
> From: Ye Bin <yebin10@huawei.com>
> 
> There's issue as follows when do test with memory fault injection:
> [localhost]# fsck.ext4 -a image
> image: clean, 45595/655360 files, 466841/2621440 blocks
> [localhost]# fsck.ext4 -fn image
> Pass 1: Checking inodes, blocks, and sizes
> Pass 2: Checking directory structure
> Pass 3: Checking directory connectivity
> Pass 4: Checking reference counts
> Pass 5: Checking group summary information
> Block bitmap differences:  -(1457230--1457256)
> Fix? no
> 
> image: ********** WARNING: Filesystem still has errors **********
> 
> image: 45595/655360 files (12.4% non-contiguous), 466841/2621440 blocks
> 
> Inject context:
>   -----------------------------------------------------------
>   Inject function:kmem_cache_alloc (pid:177858) (return: 0)
>   Calltrace Context:
>   mem_cache_allock+0x73/0xcc
>   ext4_mb_new_blocks+0x32e/0x540 [ext4]
>   ext4_new_meta_blocks+0xc4/0x110 [ext4]
>   ext4_ext_grow_indepth+0x68/0x250 [ext4]
>   ext4_ext_create_new_leaf+0xc5/0x120 [ext4]
>   ext4_ext_insert_extent+0x1bf/0x670 [ext4]
>   ext4_split_extent_at+0x212/0x530 [ext4]
>   ext4_split_extent+0x13a/0x1a0 [ext4]
>   ext4_ext_handle_unwritten_extents+0x13d/0x240 [ext4]
>   ext4_ext_map_blocks+0x459/0x8f0 [ext4]
>   ext4_map_blocks+0x18e/0x5a0 [ext4]
>   ext4_iomap_alloc+0xb0/0x1b0 [ext4]
>   ext4_iomap_begin+0xb0/0x130 [ext4]
>   iomap_apply+0x95/0x2e0
>   __iomap_dio_rw+0x1cc/0x4b0
>   iomap_dio_rw+0xe/0x40
>   ext4_dio_write_iter+0x1a9/0x390 [ext4]
>   new_sync_write+0x113/0x1b0
>   vfs_write+0x1b7/0x250
>   ksys_write+0x5f/0xe0
>   do_syscall_64+0x33/0x40
>   entry_SYSCALL_64_after_hwframe+0x61/0xc6
> 
> Compare extent change in journal:
> Start:
> ee_block      ee_len        ee_start
> 75            32798         1457227  -> unwritten len=30
> 308           12            434489
> 355           5             442492
> =>
> ee_block      ee_len        ee_start
> 11            2             951584
> 74            32769         951647   -> unwritten  len=1
> 75            32771         1457227  -> unwritten  len=3, length decreased 27
> 211           15            960906
> 308           12            434489
> 355           5             442492
> 
> Acctually, above issue can repaired by 'fsck -fa'. But file system is 'clean',
> 'fsck' will not do deep repair.
> Obviously, final lost 27 blocks. Above issue may happens as follows:
> ext4_split_extent_at
> ...
> err = ext4_ext_insert_extent(handle, inode, ppath, &newex, flags); -> return -ENOMEM
> if (err != -ENOSPC && err != -EDQUOT）
> 	goto out; -> goto 'out' will not fix extent length, will
> ...
> fix_extent_len:
>          ex->ee_len = orig_ex.ee_len;
>          /*
>           * Ignore ext4_ext_dirty return value since we are already in error path
>           * and err is a non-zero error code.
>           */
>          ext4_ext_dirty(handle, inode, path + path->p_depth);
>          return err;
> out:
>          ext4_ext_show_leaf(inode, path);
>          return err;
> If 'ext4_ext_insert_extent' return '-ENOMEM' which will not fix 'ex->ee_len' by
> old length. 'ext4_ext_insert_extent' will trigger extent tree merge, fix like
> 'ex->ee_len = orig_ex.ee_len' may lead to new issues.
> To solve above issue, record error messages when 'ext4_ext_insert_extent' return
> 'err' not equal '(-ENOSPC && -EDQUOT)'. If filesysten is mounted with 'errors=continue'
> as filesystem is not clean 'fsck' will repair issue. If filesystem is mounted with
> 'errors=remount-ro' filesystem will be remounted by read-only.
> 
> Signed-off-by: Ye Bin <yebin10@huawei.com>
> ---
>   fs/ext4/extents.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index f1956288307f..582a7d59d6e3 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -3252,8 +3252,13 @@ static int ext4_split_extent_at(handle_t *handle,
>   		ext4_ext_mark_unwritten(ex2);
>   
>   	err = ext4_ext_insert_extent(handle, inode, ppath, &newex, flags);
> -	if (err != -ENOSPC && err != -EDQUOT)
> +	if (err != -ENOSPC && err != -EDQUOT) {
> +		if (err)
> +			EXT4_ERROR_INODE_ERR(inode, -err,
> +			"insert extent failed block = %d len = %d",
> +			ex2->ee_block, ex2->ee_len);
>   		goto out;
> +	}
>   
>   	if (EXT4_EXT_MAY_ZEROOUT & split_flag) {
>   		if (split_flag & (EXT4_EXT_DATA_VALID1|EXT4_EXT_DATA_VALID2)) {
>