linux-ext4 - Re: [BUG] ext2/3/4: dio reads stale data when we do some append dio writes

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]

Date:	Tue, 19 Nov 2013 19:19:47 +0800
From:	Zheng Liu <gnehzuil.liu@...il.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [BUG] ext2/3/4: dio reads stale data when we do some append dio
 writes

On Tue, Nov 19, 2013 at 03:01:47AM -0800, Christoph Hellwig wrote:
> On Tue, Nov 19, 2013 at 06:45:08PM +0800, Zheng Liu wrote:
> > BTW, that would be great if you could give me some comments about this
> > problem itself.  Is it a generic problem in vfs?  Or just a feature by
> > design?
> 
> It seems like a fundamental issue with ext4 (and most older Linux
> filesystems) trying to do dio reads without locking out writers.

Ah, that is a long story for me.  Anyway, thanks for your comment.

> 
> If you have a shared/exclusive lock to protect dio reads against
> buffered or appending writers like XFS does this issue is properly
> prevented.

Yes, I know that XFS has a shared/exclusive lock.  I guess that is why
it can pass the test.  But another question is why xfs fails when we do
some append dio writes with doing buffered read.

Regards,
                                                - Zheng
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html