linux-kernel - Re: [PATCH v6 10/13] xfs: iomap COW-based atomic write support

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <f8cdd6b1-fcd5-4783-9fdf-bcb6e7c3e992@oracle.com>
Date: Thu, 20 Mar 2025 09:49:44 +0000
From: John Garry <john.g.garry@...cle.com>
To: Christoph Hellwig <hch@....de>
Cc: brauner@...nel.org, djwong@...nel.org, cem@...nel.org, dchinner@...hat.com,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, ojaswin@...ux.ibm.com,
        ritesh.list@...il.com, martin.petersen@...cle.com, tytso@....edu,
        linux-ext4@...r.kernel.org
Subject: Re: [PATCH v6 10/13] xfs: iomap COW-based atomic write support

On 20/03/2025 05:29, Christoph Hellwig wrote:
> On Wed, Mar 19, 2025 at 10:24:55AM +0000, John Garry wrote:
>> it seems to work ok, cheers
> 
> Better test it very well, this was really just intended as a sketch..

Sure, I have been testing a lot so far.

I had been using fio in verify mode as a method to check racing threads 
reading and atomically writing the same file range, so I need to ensure 
that it covers the various paths in this function.

> 
>>> +	count_fsb = end_fsb - offset_fsb;
>>> +	resaligned = xfs_aligned_fsb_count(offset_fsb, count_fsb,
>>> +			xfs_get_cowextsz_hint(ip));
>>> +	xfs_iunlock(ip, XFS_ILOCK_EXCL);
>>> +
>>> +	error = xfs_trans_alloc_inode(ip, &M_RES(mp)->tr_write,
>>> +			XFS_DIOSTRAT_SPACE_RES(mp, resaligned), 0, false, &tp);
>>>    	if (error)
>>>    		return error;
>>>    -	error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb, &imap,
>>> -			&nimaps, 0);
>>> -	if (error)
>>> -		goto out_unlock;
>>> +	if (!xfs_iext_lookup_extent(ip, ip->i_cowfp, offset_fsb, &icur, &cmap))
>>> +		cmap.br_startoff = end_fsb;
>>
>> Do we really need this logic?
>>
>> offset_fsb does not change, and logically cmap.br_startoff == end_fsb
>> already, right?
> 
> Afte unlocking and relocking the ilock the extent layout could have
> changed.

ok, understood. Maybe a comment will help understanding that.

>