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

[Jaegeuk Kim <jaegeuk@kernel.org>]

Hi Chao,

On 06/29, Chao Yu via Linux-f2fs-devel wrote:
> 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

Have we reproduced this?

> 
> Fixes: f5a53edcf01e ("f2fs: support aligned pinned file")
> Cc: stable@kernel.org
> Cc: Daeho Jeong <daehojeong@google.com>
> Signed-off-by: Chao Yu <chao@kernel.org>
> ---
>  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;
> +			/*
> +			 * 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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