Re: [f2fs-dev] [PATCH 1/2] f2fs: fix wrong extent_info data for precache extents

[Chao Yu <chao@kernel.org>]

On 9/10/25 21:58, wangzijie wrote:
> When the data layout is like this:
> dnode1:                     dnode2:
> [0]      A                  [0]    NEW_ADDR
> [1]      A+1                [1]    0x0
> ...                         ....
> [1016]   A+1016
> [1017]   B (B!=A+1017)      [1017] 0x0
> 
> We can build this kind of layout by following steps(with i_extra_isize:36):
> ./f2fs_io write 1 0 1881 rand dsync testfile
> ./f2fs_io write 1 1881 1 rand buffered testfile
> ./f2fs_io fallocate 0 7708672 4096 testfile
> 
> And when we map first data block in dnode2, we will get wrong extent_info data:
> map->m_len = 1
> ofs = start_pgofs - map->m_lblk = 1882 - 1881 = 1
> 
> ei.fofs = start_pgofs = 1882
> ei.len = map->m_len - ofs = 1 - 1 = 0

Hi Zijie,

I tried to reproduce w/ below steps:

f2fs_io write 1 0 1881 rand dsync testfile
f2fs_io write 1 1881 1 rand buffered testfile
f2fs_io fallocate 0 7708672 4096 testfile
umount
mount
f2fs_io precache_extents testfile

         f2fs_io-921     [013] .....  1049.855817: f2fs_lookup_start: dev = (253,16), pino = 3, name:testfile, flags:65537
         f2fs_io-921     [013] .....  1049.855870: f2fs_submit_read_bio: dev = (253,16)/(253,16), rw = READ(), DATA, sector = 139280, size = 4096
         f2fs_io-921     [013] .....  1049.856116: f2fs_submit_folio_bio: dev = (253,16), ino = 1, folio_index = 0x5, oldaddr = 0x5553, newaddr = 0x5553, rw = READ(), type = HOT_NODE
         f2fs_io-921     [013] .....  1049.856147: f2fs_submit_read_bio: dev = (253,16)/(253,16), rw = READ(), NODE, sector = 174744, size = 4096
         f2fs_io-921     [013] .....  1049.856273: f2fs_iget: dev = (253,16), ino = 5, pino = 3, i_mode = 0x81ed, i_size = 7712768, i_nlink = 1, i_blocks = 15080, i_advise = 0x0
         f2fs_io-921     [013] .....  1049.856305: f2fs_lookup_end: dev = (253,16), pino = 3, name:testfile, ino:5, err:0
         f2fs_io-921     [013] .....  1049.856316: f2fs_lookup_extent_tree_start: dev = (253,16), ino = 5, pgofs = 0, type = Read
         f2fs_io-921     [013] .....  1049.856317: f2fs_lookup_read_extent_tree_end: dev = (253,16), ino = 5, pgofs = 0, read_ext_info(fofs: 0, len: 512, blk: 1055744)
         f2fs_io-921     [013] .....  1049.856317: f2fs_map_blocks: dev = (253,16), ino = 5, file offset = 0, start blkaddr = 0x101c00, len = 0x200, flags = 2, seg_type = 8, may_create = 0, multidevice = 0, flag = 6, err = 0
         f2fs_io-921     [013] .....  1049.856318: f2fs_lookup_extent_tree_start: dev = (253,16), ino = 5, pgofs = 512, type = Read
         f2fs_io-921     [013] .....  1049.856318: f2fs_lookup_read_extent_tree_end: dev = (253,16), ino = 5, pgofs = 512, read_ext_info(fofs: 0, len: 0, blk: 0)
         f2fs_io-921     [013] .....  1049.856323: f2fs_update_read_extent_tree_range: dev = (253,16), ino = 5, pgofs = 512, len = 352, blkaddr = 18432, c_len = 0
         f2fs_io-921     [013] .....  1049.856328: f2fs_submit_folio_bio: dev = (253,16), ino = 1, folio_index = 0x6, oldaddr = 0x5556, newaddr = 0x5556, rw = READ(), type = HOT_NODE
         f2fs_io-921     [013] .....  1049.856329: f2fs_submit_read_bio: dev = (253,16)/(253,16), rw = READ(), NODE, sector = 174768, size = 4096
         f2fs_io-921     [021] .....  1049.856968: f2fs_update_read_extent_tree_range: dev = (253,16), ino = 5, pgofs = 864, len = 160, blkaddr = 18784, c_len = 0
         f2fs_io-921     [021] .....  1049.857002: f2fs_map_blocks: dev = (253,16), ino = 5, file offset = 512, start blkaddr = 0x4800, len = 0x200, flags = 2, seg_type = 8, may_create = 0, multidevice = 0, flag = 6, err = 0
         f2fs_io-921     [021] .....  1049.857003: f2fs_lookup_extent_tree_start: dev = (253,16), ino = 5, pgofs = 1025, type = Read
         f2fs_io-921     [021] .....  1049.857004: f2fs_lookup_read_extent_tree_end: dev = (253,16), ino = 5, pgofs = 1025, read_ext_info(fofs: 0, len: 0, blk: 0)
         f2fs_io-921     [021] .....  1049.857010: f2fs_update_read_extent_tree_range: dev = (253,16), ino = 5, pgofs = 1025, len = 511, blkaddr = 19457, c_len = 0
         f2fs_io-921     [021] .....  1049.857011: f2fs_map_blocks: dev = (253,16), ino = 5, file offset = 1025, start blkaddr = 0x4c01, len = 0x1ff, flags = 2, seg_type = 8, may_create = 0, multidevice = 0, flag = 6, err = 0
         f2fs_io-921     [021] .....  1049.857012: f2fs_lookup_extent_tree_start: dev = (253,16), ino = 5, pgofs = 1537, type = Read
         f2fs_io-921     [021] .....  1049.857012: f2fs_lookup_read_extent_tree_end: dev = (253,16), ino = 5, pgofs = 1537, read_ext_info(fofs: 0, len: 0, blk: 0)
         f2fs_io-921     [021] .....  1049.857016: f2fs_update_read_extent_tree_range: dev = (253,16), ino = 5, pgofs = 1537, len = 344, blkaddr = 20993, c_len = 0
         f2fs_io-921     [021] .....  1049.857016: f2fs_map_blocks: dev = (253,16), ino = 5, file offset = 1537, start blkaddr = 0x5201, len = 0x158, flags = 2, seg_type = 8, may_create = 0, multidevice = 0, flag = 6, err = 0
         f2fs_io-921     [021] .....  1049.857017: f2fs_lookup_extent_tree_start: dev = (253,16), ino = 5, pgofs = 1882, type = Read
         f2fs_io-921     [021] .....  1049.857017: f2fs_lookup_read_extent_tree_end: dev = (253,16), ino = 5, pgofs = 1882, read_ext_info(fofs: 0, len: 0, blk: 0)
         f2fs_io-921     [021] .....  1049.857024: f2fs_submit_folio_bio: dev = (253,16), ino = 1, folio_index = 0x7, oldaddr = 0x5555, newaddr = 0x5555, rw = READ(), type = HOT_NODE
         f2fs_io-921     [021] .....  1049.857026: f2fs_submit_read_bio: dev = (253,16)/(253,16), rw = READ(), NODE, sector = 174760, size = 4096
         f2fs_io-921     [021] .....  1049.857156: f2fs_map_blocks: dev = (253,16), ino = 5, file offset = 1882, start blkaddr = 0x5201, len = 0x0, flags = 0, seg_type = 8, may_create = 0, multidevice = 0, flag = 6, err = 0

It seems f2fs_update_read_extent_tree_range() won't insert a zero-sized extent?
Or am I missing something?

Thanks,

> 
> Fix it by skipping updating this kind of extent info.
> 
> Signed-off-by: wangzijie <wangzijie1@honor.com>
> ---
>  fs/f2fs/data.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 7961e0ddf..b8bb71852 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -1649,6 +1649,9 @@ int f2fs_map_blocks(struct inode *inode, struct f2fs_map_blocks *map, int flag)
>  
>  		switch (flag) {
>  		case F2FS_GET_BLOCK_PRECACHE:
> +			if (__is_valid_data_blkaddr(map->m_pblk) &&
> +				start_pgofs - map->m_lblk == map->m_len)
> +				map->m_flags &= ~F2FS_MAP_MAPPED;
>  			goto sync_out;
>  		case F2FS_GET_BLOCK_BMAP:
>  			map->m_pblk = 0;