Re: [PATCH 1/4] vfs: ftruncate freeze protect backing inode

[Amir Goldstein <amir73il@gmail.com>]

On Thu, Apr 6, 2017 at 11:13 AM, Amir Goldstein <amir73il@gmail.com> wrote:
> ftruncate an overlayfs inode was wrongly freeze protecting the
> overlay file system instead of the backing file system.
>
> Use file_start_write() instead of sb_start_write(), which
> does the right thing and will also freeze protect both overlay and
> backing fs when the time comes.
>
> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> ---
>  fs/open.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/open.c b/fs/open.c
> index 949cef2..53b1b33 100644
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -196,13 +196,13 @@ static long do_sys_ftruncate(unsigned int fd, loff_t length, int small)
>         if (IS_APPEND(inode))
>                 goto out_putf;
>
> -       sb_start_write(inode->i_sb);
> +       file_start_write(f.file);

Nah! this is wrong.
Should be mnt_want_write_file(f.file)

At the time of this patch mnt_want_write_file(f.file) translated to
sb_start_write(inode->i_sb)
but when next patch is going to change inode = file_inode(f.file)
sb_start_write(inode->i_sb) will no longer be correct
and mnt_want_write_file(f.file) is nicer than sb_start_write(locks_inode(f.file)


>         error = locks_verify_truncate(inode, f.file, length);
>         if (!error)
>                 error = security_path_truncate(&f.file->f_path);
>         if (!error)
>                 error = do_truncate(dentry, length, ATTR_MTIME|ATTR_CTIME, f.file);
> -       sb_end_write(inode->i_sb);
> +       file_end_write(f.file);
>  out_putf:
>         fdput(f);
>  out:
> --
> 2.7.4
>