linux-kernel - Re: linux-next regression: IO errors in with ext4 and xen-blkfront

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Message-ID: <4CC1515E.6080006@kernel.dk>
Date:	Fri, 22 Oct 2010 10:54:54 +0200
From:	Jens Axboe <axboe@...nel.dk>
To:	Christoph Hellwig <hch@...radead.org>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	Theodore Ts'o <tytso@....edu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Xen-devel@...ts.xensource.com" <Xen-devel@...ts.xensource.com>
Subject: Re: linux-next regression: IO errors in with ext4 and xen-blkfront

On 2010-10-22 10:29, Christoph Hellwig wrote:
> In the barriers tree Xen claims to support flushes, but I doesn't.
> It never handles REQ_FLUSH requests.  Try commenting out the
> 
> 	blk_queue_flush(info->rq, info->feature_flush);
> 
> call and things should improve.  I still need to hear back from Xen
> folks how to actually implement a cache flush - they only implement
> a barrier write privilegue which could never implement an empty
> cache flush.  Up to current kernels that meant it would implement
> barrier writes with content correctly and silently ignore empty barriers
> leading to very interesting data integrity bugs.  From 2.6.37 onwards
> it simply won't work anymore at all, which is at least consistent
> (modulo the bug of actually claiming to support flushes).

So how about we just disable barriers for Xen atm? I would really really
like to push that branch out as well now, since I'll be travelling for
most of the merge window this time.

-- 
Jens Axboe

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