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Subject: Re: [PATCH 1/4] xfs: match lock mode in
 xfs_buffered_write_iomap_begin()
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
 linux-kernel@vger.kernel.org, hch@infradead.org, brauner@kernel.org,
 david@fromorbit.com, tytso@mit.edu, jack@suse.cz, yi.zhang@huawei.com,
 chengzhihao1@huawei.com, yukuai3@huawei.com
References: <20240311122255.2637311-1-yi.zhang@huaweicloud.com>
 <20240311122255.2637311-2-yi.zhang@huaweicloud.com>
 <20240311153415.GS1927156@frogsfrogsfrogs>
From: Zhang Yi <yi.zhang@huaweicloud.com>
Message-ID: <04c14e02-9968-3fda-39a6-c3b44c78a2ba@huaweicloud.com>
Date: Tue, 12 Mar 2024 16:18:33 +0800
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On 2024/3/11 23:34, Darrick J. Wong wrote:
> On Mon, Mar 11, 2024 at 08:22:52PM +0800, Zhang Yi wrote:
>> From: Zhang Yi <yi.zhang@huawei.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?  

Yes.

> And xfs_buffered_write_iomap_begin
> sets it to EXCL (and never changes it), right?

Yes.

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

Yes, it's not a real problem.

> If the answers are {yes, yes, yes} then:
> Reviewed-by: Darrick J. Wong <djwong@kernel.org>
> 
> --D
> 
> 
>> Signed-off-by: Zhang Yi <yi.zhang@huawei.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
>>
>>