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

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Message-ID: <20110223214227.GL4020@noexit>
Date:	Wed, 23 Feb 2011 13:42:27 -0800
From:	Joel Becker <jlbec@...lplan.org>
To:	Chris Mason <chris.mason@...cle.com>
Cc:	"Martin K. Petersen" <martin.petersen@...cle.com>,
	djwong <djwong@...ibm.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 Wed, Feb 23, 2011 at 03:35:11PM -0500, Chris Mason wrote:
> >     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
> sure you don't free blocks back to the allocator that are actively under
> IO.
> 
> I expect the hard part to be jbd and metadata in ext34.

	Yeah, catching use-without-access is not trivial.  I keep
thinking we've found them all, and then another bug crops up ;-)  At
least our checksums catch it.

Joel

-- 

"The doctrine of human equality reposes on this: that there is no
 man really clever who has not found that he is stupid."
	- Gilbert K. Chesterson

			http://www.jlbec.org/
			jlbec@...lplan.org
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