Re: [f2fs-dev] [PATCH] f2fs: fix to avoid potential section-unaligned pinfile

[Zhiguo Niu]

Chao Yu via Linux-f2fs-devel <linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx>
于2026年6月29日周一 19:52写道：
>
> Blocks of pinfile may not aligned to section size due to wrong use
> on pinfile, result in heavy overhead of GC, let avoid this by
> adding additional check condition in f2fs_setattr().
>
> - truncate -s 8mb pinfile
> : random checkpoint may persist filesize w/ inode
> - fallocate -o 0 -l 8mb pinfile
>  - f2fs_fallocate
>   - f2fs_expand_inode_data
>    - f2fs_allocate_pinning_section
>    - f2fs_map_blocks
>     - f2fs_map_lock
>     - __allocate_data_block
>     - file_need_truncate
>     : w/ FADVISE_TRUNC_BIT, we can expect unaligned mapping can be
>       truncated while open() if f2fs is not umount abnormally
>     - f2fs_map_unlock
>     : following f2fs checkpoint and sudden power-cut
>
> - mount
> - open pinfile
>  - f2fs_file_open
>   - finish_preallocate_blocks
>    - truncate_setsize
>    : filesize is 8mb
>    - f2fs_truncate
>    : can only truncate block outside filesize, rather than truncating
>      unaligned blocks inside filesize
Hi Chao,
8MB is section alinged when fallocated by f2fs_allocate_pinning_section??
so How could there are unaligned blocks inside filesize?
>
> Fixes: f5a53edcf01e ("f2fs: support aligned pinned file")
> Cc: stable@xxxxxxxxxx
> Cc: Daeho Jeong <daehojeong@xxxxxxxxxx>
> Signed-off-by: Chao Yu <chao@xxxxxxxxxx>
> ---
>  fs/f2fs/file.c | 28 +++++++++++++++++-----------
>  1 file changed, 17 insertions(+), 11 deletions(-)
>
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index f4facd409d9b..11cc8d79c235 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -1107,17 +1107,23 @@ int f2fs_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
>                         !IS_ALIGNED(attr->ia_size,
>                         F2FS_BLK_TO_BYTES(fi->i_cluster_size)))
>                         return -EINVAL;
> -               /*
> -                * To prevent scattered pin block generation, we don't allow
> -                * smaller/equal size unaligned truncation for pinned file.
> -                * We only support overwrite IO to pinned file, so don't
> -                * care about larger size truncation.
> -                */
> -               if (f2fs_is_pinned_file(inode) &&
> -                       attr->ia_size <= i_size_read(inode) &&
> -                       !IS_ALIGNED(attr->ia_size,
> -                       F2FS_BLK_TO_BYTES(CAP_BLKS_PER_SEC(sbi))))
> -                       return -EINVAL;
> +
> +               if (f2fs_is_pinned_file(inode)) {
> +                       /*
> +                        * It may break section-aligned fallocate recovery
> +                        * mechanism, so do not allow larger size truncation.
> +                        */
> +                       if (attr->ia_size > i_size_read(inode))
> +                               return -EINVAL;
Is it ok if we allow larger size truncation and also  limit it to
aligned "F2FS_BLK_TO_BYTES(CAP_BLKS_PER_SEC(sbi)"?
thanks!
> +                       /*
> +                        * To prevent scattered pin block generation, we don't
> +                        * allow smaller/equal size unaligned truncation for
> +                        * pinned file.
> +                        */
> +                       else if (!IS_ALIGNED(attr->ia_size,
> +                               F2FS_BLK_TO_BYTES(CAP_BLKS_PER_SEC(sbi))))
> +                               return -EINVAL;
> +               }
>         }
>
>         if (is_quota_modification(idmap, inode, attr)) {
> --
> 2.49.0
>
>
>
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