Re: [PATCH v2] f2fs: fix i_size when pinned fallocate partially fails

[Chao Yu]

On 8/18/26 22:55, Zhan Xusheng wrote:
> From: Zhan Xusheng <zhanxusheng1024@xxxxxxxxx>
> 
> From: Zhan Xusheng <zhanxusheng@xxxxxxxxxx>
> 
> Commit 4275b59673eb ("f2fs: fix to round down start offset of fallocate
> for pin file") moved the allocation loop's start down to a section
> boundary, but the error path still converts @expanded against @pg_start,
> which holds the unrounded start.
> 
> @pg_start exists for that conversion: commit 88f2cfc5fa90 ("f2fs: fix to
> update last i_size if fallocate partially succeeds") added it as an
> immutable base because map.m_lblk moves every round.  Each round now maps
> exactly sec_blks blocks starting from rounddown(pg_start, sec_blks), so
> pg_start + expanded overshoots the last allocated block by
> pg_start % sec_blks, and a partial failure leaves i_size covering a tail
> that was never allocated.  Nothing corrects that afterwards either, since
> file_dont_truncate() has already cleared FADVISE_TRUNC_BIT.
> 
> It needs a start offset that is not section aligned plus a fallocate that
> hits ENOSPC partway, so the error path runs with expanded > 0.  On an
> 80 MiB image with 2 MiB sections:
> 
>   truncate -s 80M img
>   mkfs.f2fs -s 1 -f img
>   mount -o loop img /mnt
>   touch /mnt/pinned
>   f2fs_io pinfile set /mnt/pinned
>   # 2093056 = block 511, so pg_start % sec_blks = 511
>   f2fs_io fallocate 0 2093056 536870912 /mnt/pinned
>   stat -c %s /mnt/pinned
>   filefrag -v /mnt/pinned
> 
> The last extent ends at block 10737 either way.  Before, i_size is
> 46075904, block 11249, so 511 blocks of it were never allocated, and
> filefrag does not mark the last extent eof.  After, i_size is 43982848,
> block 10738, and eof is back.  A kernel from before that commit also
> shows no overshoot.
> 
> Keep @pg_start pointing at where allocation actually begins.
> 
> Fixes: 4275b59673eb ("f2fs: fix to round down start offset of fallocate for pin file")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Zhan Xusheng <zhanxusheng@xxxxxxxxxx>
Reviewed-by: Chao Yu <chao@xxxxxxxxxx>

Thanks,