linux-kernel - Re: [PATCH v3 11/13] fs: use smp_load_acquire in break

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Date:   Fri, 20 Oct 2017 08:39:11 -0400
From:   Jeffrey Layton <jlayton@...nel.org>
To:     Dan Williams <dan.j.williams@...el.com>, akpm@...ux-foundation.org
Cc:     linux-xfs@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-kernel@...r.kernel.org, hch@....de,
        "J. Bruce Fields" <bfields@...ldses.org>, linux-mm@...ck.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org,
        Ross Zwisler <ross.zwisler@...ux.intel.com>
Subject: Re: [PATCH v3 11/13] fs: use smp_load_acquire in
 break_{layout,lease}

On Thu, 2017-10-19 at 19:39 -0700, Dan Williams wrote:
> Commit 128a37852234 "fs: fix data races on inode->i_flctx" converted
> checks of inode->i_flctx to use smp_load_acquire(), but it did not
> convert break_layout(). smp_load_acquire() includes a READ_ONCE(). There
> should be no functional difference since __break_lease repeats the
> sequence, but this is a clean up to unify all ->i_flctx lookups on a
> common pattern.
> 
> Cc: Christoph Hellwig <hch@....de>
> Cc: Alexander Viro <viro@...iv.linux.org.uk>
> Cc: Ross Zwisler <ross.zwisler@...ux.intel.com>
> Cc: Jeff Layton <jlayton@...chiereds.net>
> Cc: "J. Bruce Fields" <bfields@...ldses.org>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> ---
>  include/linux/fs.h |   10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 13dab191a23e..eace2c5396a7 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2281,8 +2281,9 @@ static inline int break_lease(struct inode *inode, unsigned int mode)
>  	 * could end up racing with tasks trying to set a new lease on this
>  	 * file.
>  	 */
> -	smp_mb();
> -	if (inode->i_flctx && !list_empty_careful(&inode->i_flctx->flc_lease))
> +	struct file_lock_context *ctx = smp_load_acquire(&inode->i_flctx);
> +
> +	if (ctx && !list_empty_careful(&ctx->flc_lease))
>  		return __break_lease(inode, mode, FL_LEASE);
>  	return 0;
>  }
> @@ -2325,8 +2326,9 @@ static inline int break_deleg_wait(struct inode **delegated_inode)
>  
>  static inline int break_layout(struct inode *inode, bool wait)
>  {
> -	smp_mb();
> -	if (inode->i_flctx && !list_empty_careful(&inode->i_flctx->flc_lease))
> +	struct file_lock_context *ctx = smp_load_acquire(&inode->i_flctx);
> +
> +	if (ctx && !list_empty_careful(&ctx->flc_lease))
>  		return __break_lease(inode,
>  				wait ? O_WRONLY : O_WRONLY | O_NONBLOCK,
>  				FL_LAYOUT);
> 

Nice catch. This can go in independently of the rest of the patches in
the series, I think. I'll assume Andrew is picking this up since he's in
the "To:", but let me know if you need me to get it.

Reviewed-by: Jeff Layton <jlayton@...nel.org>