linux-kernel - Re: [PATCH] dm: dm-cache fails to write the cache device in writethrough mode

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Message-ID: <20130322205005.GD5371@blackbox.djwong.org>
Date:	Fri, 22 Mar 2013 13:50:05 -0700
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	Ben Hutchings <ben@...adent.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	dm-devel@...hat.com, linux-kernel@...r.kernel.org,
	Heinz Mauelshagen <heinzm@...hat.com>,
	Joe Thornber <ejt@...hat.com>,
	Mike Snitzer <snitzer@...hat.com>,
	Mikulas Patocka <mpatocka@...hat.com>,
	Paul Taysom <taysom@...omium.org>,
	Randy Dunlap <rdunlap@...radead.org>, stable@...r.kernel.org
Subject: Re: [PATCH] dm: dm-cache fails to write the cache device in
 writethrough mode

On Fri, Mar 22, 2013 at 08:21:56PM +0000, Ben Hutchings wrote:
> On Fri, 2013-03-22 at 13:11 -0700, Darrick J. Wong wrote:
> > The new writethrough strategy for dm-cache issues a bio to the origin device,
> > remaps the bio to the cache device, and issues the bio to the cache device.
> > However, the block layer modifies bi_sector and bi_size, so we need to preserve
> > these or else nothing gets written to the cache (bi_size == 0).  This fixes the
> > problem where someone writes a block through the cache, but a subsequent reread
> > (from the cache) returns old contents.
> > 
> > Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
> > ---
> [...]
> 
> This is not the correct way to submit a change to stable.  See
> Documentation/stable_kernel_rules.txt

Frankly, I'm not sure why agk sent the 3.9-fixes pull request to -stable.  7 of
the 10 commits are for dm-cache, and dm-cache is a new feature for 3.9.  I
probably could have dropped -stable from the cc: list when I started
complaining about bugs.  :)

Sorry about the noise.

--D
> 
> Ben.
> 
> -- 
> Ben Hutchings
> Make three consecutive correct guesses and you will be considered an expert.


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