Re: Can ovl_drop_write() be called earlier in ovl_dentry_open()

[Miklos Szeredi <miklos@szeredi.hu>]

On Mon, Jun 1, 2015 at 3:52 PM, David Howells <dhowells@redhat.com> wrote:
> In ovl_dentry_open(), ovl_drop_write() is called after vfs_open() - but is
> this actually necessary?  Can't we just drop it post-copyup?  After all,
> that's all we wanted the write lock for, right?

Hmm,  that could result in a race where remount r/o of upper fs comes
in between copy-up and vfs_open() so copy-up succeeds but the actual
open fails.  It's harmless, though, and not  very likely.  So I guess
your patch is OK.

Thanks,
Miklos




>
> David
> ---
> --- a/fs/overlayfs/inode.c
> +++ b/fs/overlayfs/inode.c
> @@ -356,16 +356,14 @@ static int ovl_dentry_open(struct dentry *dentry, struct inode *inode,
>                         err = ovl_copy_up_last(dentry, NULL, true);
>                 else
>                         err = ovl_copy_up(dentry);
> +               ovl_drop_write(dentry);
>                 if (err)
> -                       goto out_drop_write;
> +                       goto out;
>
>                 ovl_path_upper(dentry, &realpath);
>         }
>
>         err = vfs_open(&realpath, d_backing_inode(realpath.dentry), file, cred);
> -out_drop_write:
> -       if (want_write)
> -               ovl_drop_write(dentry);
>  out:
>         return err;
>  }