linux-kernel - Re: [RFC] block integrity: Fix write after checksum calculation problem

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Message-ID: <20110311185118.GB1110@tux1.beaverton.ibm.com>
Date:	Fri, 11 Mar 2011 10:51:18 -0800
From:	"Darrick J. Wong" <djwong@...ibm.com>
To:	Chris Mason <chris.mason@...cle.com>
Cc:	Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.cz>,
	Joel Becker <jlbec@...lplan.org>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Jens Axboe <axboe@...nel.dk>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Mingming Cao <mcao@...ibm.com>,
	linux-scsi <linux-scsi@...r.kernel.org>
Subject: Re: [RFC] block integrity: Fix write after checksum calculation
	problem

On Fri, Mar 11, 2011 at 11:34:05AM -0500, Chris Mason wrote:
> Excerpts from Darrick J. Wong's message of 2011-03-10 18:57:22 -0500:
> > On Tue, Mar 08, 2011 at 03:56:26PM +1100, Dave Chinner wrote:
> > 
> > > On Fri, Mar 04, 2011 at 01:07:24PM -0800, Darrick J. Wong wrote:
> > > > On Mon, Feb 28, 2011 at 07:54:05AM -0500, Chris Mason wrote:
> > > > > Excerpts from Darrick J. Wong's message of 2011-02-24 13:27:32 -0500:
> > > > > > On Thu, Feb 24, 2011 at 12:37:53PM -0500, Chris Mason wrote:
> > > > > > > Excerpts from Jan Kara's message of 2011-02-24 11:47:58 -0500:
> > > > > > > > On Wed 23-02-11 15:35:11, Chris Mason wrote:
> > > > > > > > > Excerpts from Joel Becker's message of 2011-02-23 15:24:47 -0500:
> > > > > > > > > > On Tue, Feb 22, 2011 at 11:45:44AM -0500, Martin K. Petersen wrote:
> > > > > > > > > > > Also, DIX is only the tip of the iceberg. Many other impending
> > > > > > > > > > > technologies feature checksums and require pages to be stable during I/O
> > > > > > > > > > > due to checksumming, encryption and so on.
> > > > > > > > > > > 
> > > > > > > > > > > The VM is already trying to do the right thing. We just need the
> > > > > > > > > > > relevant filesystems to catch up.
> > > > > > > > > > 
> > > > > > > > > >     ocfs2 handles stable metadata for its checksums when feeding
> > > > > > > > > > things to the journal.  If we're doing pagecache-based I/O, is the
> > > > > > > > > > pagecache going to help here for data?
> > > > > > > > > 
> > > > > > > > > Data is much easier than metadata.  All you really need is to wait on
> > > > > > > > > writeback in file_write, wait on writeback in page_mkwrite, and make
> > 
> > Hrm... I've been looking for a file_write in ext4; was the aio_write function
> > pointer what you had in mind here?
> 
> Your change to grab_cache_page_write_begin looks good to me, at least
> for ext4.  For ext3 you have to actually go in and wait for each of the
> buffer heads in the page, since ext3 (and reiserfs) will write the buffer heads
> directly without using writepage.

Heh, I hadn't really given much thought to ext2/3 yet.  I'm still trying to
figure out what causes the occasional ext4 failures. :)

> Have you confirmed by looking at the block mapping that your crc errors
> are from data blocks?

Yes, debugfs confirms that they are data blocks.

--D
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