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Date: Thu, 23 Feb 2012 09:12:12 +0000
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20120223091212.GA10575@stefanha-thinkpad.localdomain>
References: <20120222214959.20738.46143.malonedeb@soybean.canonical.com>
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Subject: Re: [Qemu-devel] [Bug 939027] [NEW] Combining direct_io and
 non-direct_io leads to hang
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To: Avleen Vig <939027@bugs.launchpad.net>
Cc: qemu-devel@nongnu.org

On Wed, Feb 22, 2012 at 09:49:59PM -0000, Avleen Vig wrote:
> Version 0.12.2 - I know this isn't the latest but I looked through the
> changelogs and couldn't find any references to this being fixed.
>
> This is related to issues that many apps have, and is described in more detail here:
>     http://oss.sgi.com/archives/xfs/2010-07/msg00163.html
> and:
>     https://bugs.launchpad.net/percona-xtrabackup/+bug/606981
> 
> When using both direct io and buffered io on the same file, you can cause corruption on the filesystem and other issues.
> XFS out right hangs, but the problem exists on ext3 and other filesystems which silently carry on.
> 
> **this is a data corruption issue**.
> 
> This is the full stack trace we got from a recent hang:

I only see qemu-kvm in the backtrace.  QEMU normally only access the
image file either with or without O_DIRECT - not both at the same time.
Were you running another program that accesses the image file at the
same time?

Stefan