Re: [f2fs-dev] [PATCH v4 1/2] f2fs: correct i_size change for atomic writes

[Chao Yu <chao@kernel.org>]

On 2022/10/5 1:13, Daeho Jeong wrote:
> From: Daeho Jeong <daehojeong@google.com>
> 
> We need to make sure i_size doesn't change until atomic write commit is
> successful and restore it when commit is failed.
> 
> Signed-off-by: Daeho Jeong <daehojeong@google.com>
> ---
> v4: move i_size update after clearing atomic file flag in
>      f2fs_abort_atomic_write()
> v3: make sure inode is clean while atomic writing
> ---
>   fs/f2fs/f2fs.h    |  1 +
>   fs/f2fs/file.c    | 18 +++++++++++-------
>   fs/f2fs/inode.c   |  3 +++
>   fs/f2fs/segment.c |  7 +++++--
>   4 files changed, 20 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index dee7b67a17a6..539da7f12cfc 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -821,6 +821,7 @@ struct f2fs_inode_info {
>   	unsigned int i_cluster_size;		/* cluster size */
>   
>   	unsigned int atomic_write_cnt;
> +	loff_t original_i_size;		/* original i_size before atomic write */
>   };
>   
>   static inline void get_extent_info(struct extent_info *ext,
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index 5efe0e4a725a..ce2336d2f688 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -1989,6 +1989,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
>   	struct f2fs_inode_info *fi = F2FS_I(inode);
>   	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
>   	struct inode *pinode;
> +	loff_t isize;
>   	int ret;
>   
>   	if (!inode_owner_or_capable(mnt_userns, inode))
> @@ -2047,7 +2048,12 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
>   		f2fs_up_write(&fi->i_gc_rwsem[WRITE]);
>   		goto out;
>   	}
> -	f2fs_i_size_write(fi->cow_inode, i_size_read(inode));
> +
> +	f2fs_write_inode(inode, NULL);
> +
> +	isize = i_size_read(inode);
> +	fi->original_i_size = isize;
> +	f2fs_i_size_write(fi->cow_inode, isize);
>   
>   	spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
>   	sbi->atomic_files++;
> @@ -2087,16 +2093,14 @@ static int f2fs_ioc_commit_atomic_write(struct file *filp)
>   
>   	if (f2fs_is_atomic_file(inode)) {
>   		ret = f2fs_commit_atomic_write(inode);
> -		if (ret)
> -			goto unlock_out;
> -
> -		ret = f2fs_do_sync_file(filp, 0, LLONG_MAX, 0, true);
>   		if (!ret)
> -			f2fs_abort_atomic_write(inode, false);
> +			ret = f2fs_do_sync_file(filp, 0, LLONG_MAX, 0, true);
> +
> +		f2fs_abort_atomic_write(inode, ret);
>   	} else {
>   		ret = f2fs_do_sync_file(filp, 0, LLONG_MAX, 1, false);
>   	}
> -unlock_out:
> +
>   	inode_unlock(inode);
>   	mnt_drop_write_file(filp);
>   	return ret;
> diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
> index cde0a3dc80c3..64d7772b4cd9 100644
> --- a/fs/f2fs/inode.c
> +++ b/fs/f2fs/inode.c
> @@ -30,6 +30,9 @@ void f2fs_mark_inode_dirty_sync(struct inode *inode, bool sync)
>   	if (f2fs_inode_dirtied(inode, sync))
>   		return;
>   
> +	if (f2fs_is_atomic_file(inode))
> +		return;

One question, after f2fs_inode_dirtied(), atomic_file is added to
inode_list[DIRTY_META], and it will be flushed by checkpoint()
triggered in between write() and atomic_commit ioctl, is it not
expected that inode w/ new i_size will be persisted?

Should write_end() skip updating atomic_file's i_size and let
atomic_commit() update it if there is no error?

Thanks,

> +
>   	mark_inode_dirty_sync(inode);
>   }
>   
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 460048f3c850..abb55cd418c1 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -193,14 +193,17 @@ void f2fs_abort_atomic_write(struct inode *inode, bool clean)
>   	if (!f2fs_is_atomic_file(inode))
>   		return;
>   
> -	if (clean)
> -		truncate_inode_pages_final(inode->i_mapping);
>   	clear_inode_flag(fi->cow_inode, FI_COW_FILE);
>   	iput(fi->cow_inode);
>   	fi->cow_inode = NULL;
>   	release_atomic_write_cnt(inode);
>   	clear_inode_flag(inode, FI_ATOMIC_FILE);
>   
> +	if (clean) {
> +		truncate_inode_pages_final(inode->i_mapping);
> +		f2fs_i_size_write(inode, fi->original_i_size);
> +	}
> +
>   	spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
>   	sbi->atomic_files--;
>   	spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);