On 09/17, wangzijie wrote:
> Script to reproduce:
> f2fs_io write 1 0 1881 rand dsync testfile
> f2fs_io fallocate 0 7708672 4096 testfile
> f2fs_io write 1 1881 1 rand buffered testfile
> fsync testfile
> umount
> mount
> f2fs_io precache_extents testfile
>
> When the data layout is something like this:
> dnode1: dnode2:
> [0] A [0] NEW_ADDR
> [1] A+1 [1] 0x0
> ...
> [1016] A+1016
> [1017] B (B!=A+1017) [1017] 0x0
>
> During precache_extents, we map the last block(valid blkaddr) in dnode1:
> map->m_flags |= F2FS_MAP_MAPPED;
> map->m_pblk = blkaddr(valid blkaddr);
> map->m_len = 1;
> then we goto next_dnode, meet the first block in dnode2(hole), goto sync_out:
> map->m_flags & F2FS_MAP_MAPPED == true, and we make zero-sized extent:
>
> 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
>
>
> Rebased on patch[1], this patch can cover these cases to avoid zero-sized
> extent:
> A,B,C is valid blkaddr
> case1:
> dnode1: dnode2:
> [0] A [0] NEW_ADDR
> [1] A+1 [1] 0x0
> ... ....
> [1016] A+1016
> [1017] B (B!=A+1017) [1017] 0x0
>
> case2:
> dnode1: dnode2:
> [0] A [0] C (C!=B+1)
> [1] A+1 [1] C+1
> ... ....
> [1016] A+1016
> [1017] B (B!=A+1017) [1017] 0x0
>
> case3:
> dnode1: dnode2:
> [0] A [0] C (C!=B+2)
> [1] A+1 [1] C+1
> ... ....
> [1015] A+1015
> [1016] B (B!=A+1016)
> [1017] B+1 [1017] 0x0
>
> [1]
> https://lore.kernel.org/linux-f2fs-devel/20250912081250.44383-1-c...@kernel.org/
>
> Fixes: c4020b2da4c9 ("f2fs: support F2FS_IOC_PRECACHE_EXTENTS")
> Signed-off-by: wangzijie <wangzij...@honor.com>
> ---
> Rebased on:
> https://lore.kernel.org/linux-f2fs-devel/20250912081250.44383-1-c...@kernel.org/
> v2:
> https://lore.kernel.org/linux-f2fs-devel/20250915035246.98055-1-wangzij...@honor.com/
> ---
> fs/f2fs/data.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 838eae39d..7a5170b32 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -1778,9 +1778,10 @@ int f2fs_map_blocks(struct inode *inode, struct
> f2fs_map_blocks *map, int flag)
> if (map->m_flags & F2FS_MAP_MAPPED) {
> unsigned int ofs = start_pgofs - map->m_lblk;
>
> - f2fs_update_read_extent_cache_range(&dn,
> - start_pgofs, map->m_pblk + ofs,
> - map->m_len - ofs);
> + if (map->m_len - ofs > 0)
Applied with
if (map->m_len > ofs)
> + f2fs_update_read_extent_cache_range(&dn,
> + start_pgofs, map->m_pblk + ofs,
> + map->m_len - ofs);
> }
> if (map->m_next_extent)
> *map->m_next_extent = is_hole ? pgofs + 1 : pgofs;
> --
> 2.25.1
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