linux-kernel - Re: [PATCH 1/4] xfs: match lock mode in xfs_buffered_write_iomap

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Date: Mon, 11 Mar 2024 08:34:15 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: Zhang Yi <yi.zhang@...weicloud.com>
Cc: linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, hch@...radead.org, brauner@...nel.org,
	david@...morbit.com, tytso@....edu, jack@...e.cz,
	yi.zhang@...wei.com, chengzhihao1@...wei.com, yukuai3@...wei.com
Subject: Re: [PATCH 1/4] xfs: match lock mode in
 xfs_buffered_write_iomap_begin()

On Mon, Mar 11, 2024 at 08:22:52PM +0800, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@...wei.com>
> 
> Commit 1aa91d9c9933 ("xfs: Add async buffered write support") replace
> xfs_ilock(XFS_ILOCK_EXCL) with xfs_ilock_for_iomap() when locking the
> writing inode, and a new variable lockmode is used to indicate the lock
> mode. Although the lockmode should always be XFS_ILOCK_EXCL, it's still
> better to use this variable instead of useing XFS_ILOCK_EXCL directly
> when unlocking the inode.
> 
> Fixes: 1aa91d9c9933 ("xfs: Add async buffered write support")

AFAICT, xfs_ilock_for_iomap can change lockmode from SHARED->EXCL, but
never changed away from EXCL, right?  And xfs_buffered_write_iomap_begin
sets it to EXCL (and never changes it), right?

This seems like more of a code cleanup/logic bomb removal than an actual
defect that someone could actually hit, correct?

If the answers are {yes, yes, yes} then:
Reviewed-by: Darrick J. Wong <djwong@...nel.org>

--D


> Signed-off-by: Zhang Yi <yi.zhang@...wei.com>
> ---
>  fs/xfs/xfs_iomap.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> index 18c8f168b153..ccf83e72d8ca 100644
> --- a/fs/xfs/xfs_iomap.c
> +++ b/fs/xfs/xfs_iomap.c
> @@ -1149,13 +1149,13 @@ xfs_buffered_write_iomap_begin(
>  	 * them out if the write happens to fail.
>  	 */
>  	seq = xfs_iomap_inode_sequence(ip, IOMAP_F_NEW);
> -	xfs_iunlock(ip, XFS_ILOCK_EXCL);
> +	xfs_iunlock(ip, lockmode);
>  	trace_xfs_iomap_alloc(ip, offset, count, allocfork, &imap);
>  	return xfs_bmbt_to_iomap(ip, iomap, &imap, flags, IOMAP_F_NEW, seq);
>  
>  found_imap:
>  	seq = xfs_iomap_inode_sequence(ip, 0);
> -	xfs_iunlock(ip, XFS_ILOCK_EXCL);
> +	xfs_iunlock(ip, lockmode);
>  	return xfs_bmbt_to_iomap(ip, iomap, &imap, flags, 0, seq);
>  
>  found_cow:
> @@ -1165,17 +1165,17 @@ xfs_buffered_write_iomap_begin(
>  		if (error)
>  			goto out_unlock;
>  		seq = xfs_iomap_inode_sequence(ip, IOMAP_F_SHARED);
> -		xfs_iunlock(ip, XFS_ILOCK_EXCL);
> +		xfs_iunlock(ip, lockmode);
>  		return xfs_bmbt_to_iomap(ip, iomap, &cmap, flags,
>  					 IOMAP_F_SHARED, seq);
>  	}
>  
>  	xfs_trim_extent(&cmap, offset_fsb, imap.br_startoff - offset_fsb);
> -	xfs_iunlock(ip, XFS_ILOCK_EXCL);
> +	xfs_iunlock(ip, lockmode);
>  	return xfs_bmbt_to_iomap(ip, iomap, &cmap, flags, 0, seq);
>  
>  out_unlock:
> -	xfs_iunlock(ip, XFS_ILOCK_EXCL);
> +	xfs_iunlock(ip, lockmode);
>  	return error;
>  }
>  
> -- 
> 2.39.2
> 
>