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[Xen-devel] Re: linux-next regression: IO errors in with ext4 and xen-bl

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: [Xen-devel] Re: linux-next regression: IO errors in with ext4 and xen-blkfront
From: Jens Axboe <axboe@xxxxxxxxx>
Date: Fri, 22 Oct 2010 10:54:54 +0200
Cc: Theodore Ts'o <tytso@xxxxxxx>, Jeremy Fitzhardinge <jeremy@xxxxxxxx>, "Xen-devel@xxxxxxxxxxxxxxxxxxx" <Xen-devel@xxxxxxxxxxxxxxxxxxx>, Andreas Dilger <adilger.kernel@xxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>
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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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