Re: [PATCH v2] xfs: add agf freeblocks verify in xfs_agf_verify

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Thu, Feb 20, 2020 at 07:13:02PM +0800, Zheng Bin wrote:
> We recently used fuzz(hydra) to test XFS and automatically generate
> tmp.img(XFS v5 format, but some metadata is wrong)
> 
> xfs_repair information(just one AG):
> agf_freeblks 0, counted 3224 in ag 0
> agf_longest 536874136, counted 3224 in ag 0
> sb_fdblocks 613, counted 3228
> 
> Test as follows:
> mount tmp.img tmpdir
> cp file1M tmpdir
> sync
> 
> In 4.19-stable, sync will stuck, the reason is:
> xfs_mountfs
>   xfs_check_summary_counts
>     if ((!xfs_sb_version_haslazysbcount(&mp->m_sb) ||
>        XFS_LAST_UNMOUNT_WAS_CLEAN(mp)) &&
>        !xfs_fs_has_sickness(mp, XFS_SICK_FS_COUNTERS))
> 	return 0;  -->just return, incore sb_fdblocks still be 613
>     xfs_initialize_perag_data
> 
> cp file1M tmpdir -->ok(write file to pagecache)
> sync -->stuck(write pagecache to disk)
> xfs_map_blocks
>   xfs_iomap_write_allocate
>     while (count_fsb != 0) {
>       nimaps = 0;
>       while (nimaps == 0) { --> endless loop
>          nimaps = 1;
>          xfs_bmapi_write(..., &nimaps) --> nimaps becomes 0 again
> xfs_bmapi_write
>   xfs_bmap_alloc
>     xfs_bmap_btalloc
>       xfs_alloc_vextent
>         xfs_alloc_fix_freelist
>           xfs_alloc_space_available -->fail(agf_freeblks is 0)
> 
> In linux-next, sync not stuck, cause commit c2b3164320b5 ("xfs:
> use the latest extent at writeback delalloc conversion time") remove
> the above while, dmesg is as follows:
> [   55.250114] XFS (loop0): page discard on page ffffea0008bc7380, inode 0x1b0c, offset 0.
> 
> Users do not know why this page is discard, the better soultion is:
> 1. Like xfs_repair, make sure sb_fdblocks is equal to counted
> (xfs_initialize_perag_data did this, who is not called at this mount)
> 2. Add agf verify, if fail, will tell users to repair
> 
> This patch use the second soultion.
> 
> Signed-off-by: Zheng Bin <zhengbin13@huawei.com>
> Signed-off-by: Ren Xudong <renxudong1@huawei.com>
> ---
> v1->v2: modify comment, add more agf verify
>  fs/xfs/libxfs/xfs_alloc.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
> index d8053bc..5faed42 100644
> --- a/fs/xfs/libxfs/xfs_alloc.c
> +++ b/fs/xfs/libxfs/xfs_alloc.c
> @@ -2839,6 +2839,7 @@ xfs_agf_verify(
>  {
>  	struct xfs_mount	*mp = bp->b_mount;
>  	struct xfs_agf		*agf = XFS_BUF_TO_AGF(bp);
> +	int i;
> 
>  	if (xfs_sb_version_hascrc(&mp->m_sb)) {
>  		if (!uuid_equal(&agf->agf_uuid, &mp->m_sb.sb_meta_uuid))
> @@ -2858,6 +2859,22 @@ xfs_agf_verify(
>  	      be32_to_cpu(agf->agf_flcount) <= xfs_agfl_size(mp)))
>  		return __this_address;
> 
> +	if (be32_to_cpu(agf->agf_length) > mp->m_sb.sb_dblocks ||
> +	    be32_to_cpu(agf->agf_btreeblks) > be32_to_cpu(agf->agf_length) ||

Isn't this already covered later on?

> +	    be32_to_cpu(agf->agf_rmap_blocks) > be32_to_cpu(agf->agf_length) ||
> +	    be32_to_cpu(agf->agf_refcount_blocks) > be32_to_cpu(agf->agf_length) ||

Do these fields need checking when the corresponding feature isn't
enabled?

> +	    be32_to_cpu(agf->agf_spare2) != 0)

If, for some reason, these unused "spare" fields are *not* zero, won't
this cause mount failures on existing filesystems?

> +		return __this_address;

Please try to check only one agf field per if clause, because we use the
logged __this_address to figure out which field triggered the corruption
error.

> +
> +	for (i = 0; i < ARRAY_SIZE(agf->agf_spare64); i++)
> +		if (be64_to_cpu(agf->agf_spare64[i]) != 0)
> +			return __this_address;

memchr_inv if you leave in the spare check.

> +
> +	if (be32_to_cpu(agf->agf_freeblks) < be32_to_cpu(agf->agf_longest) ||
> +	    be32_to_cpu(agf->agf_freeblks) > be32_to_cpu(agf->agf_length) ||

Already covered in this function.

--D

> +	    be32_to_cpu(agf->agf_freeblks) > mp->m_sb.sb_fdblocks)
> +		return __this_address;
> +
>  	if (be32_to_cpu(agf->agf_levels[XFS_BTNUM_BNO]) < 1 ||
>  	    be32_to_cpu(agf->agf_levels[XFS_BTNUM_CNT]) < 1 ||
>  	    be32_to_cpu(agf->agf_levels[XFS_BTNUM_BNO]) > XFS_BTREE_MAXLEVELS ||
> --
> 2.7.4
>