Re: [PATCH 1/2] locks: add missing memory barrier in break_deleg

["J. Bruce Fields" <bfields@fieldses.org>]

On Tue, Jun 10, 2014 at 04:14:35PM -0400, Jeff Layton wrote:
> break_deleg is subject to the same potential race as break_lease. Add
> a memory barrier to prevent it.

Acked-by: J. Bruce Fields <bfields@redhat.com>

Though we might now just move the comment, smp_mb(), and inode->i_flock
calls into __break_lease?

--b.

> 
> Signed-off-by: Jeff Layton <jlayton@primarydata.com>
> ---
>  include/linux/fs.h | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index c3f46e499dd0..22ae79650b82 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1914,6 +1914,12 @@ static inline int break_lease(struct inode *inode, unsigned int mode)
>  
>  static inline int break_deleg(struct inode *inode, unsigned int mode)
>  {
> +	/*
> +	 * Since this check is lockless, we must ensure that any refcounts
> +	 * taken are done before checking inode->i_flock. Otherwise, we could
> +	 * end up racing with tasks trying to set a new lease on this file.
> +	 */
> +	smp_mb();
>  	if (inode->i_flock)
>  		return __break_lease(inode, mode, FL_DELEG);
>  	return 0;
> -- 
> 1.9.3
>