Re: [Qemu-devel] [Bug 939027] [NEW] Combining direct_io and non-direct_io leads to hang

[Stefan Hajnoczi]

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