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Re: [Qemu-ppc] qemu-system-ppc64 hanging occasionally in disk writes

From: Alexander Graf
Subject: Re: [Qemu-ppc] qemu-system-ppc64 hanging occasionally in disk writes
Date: Thu, 14 Jun 2012 17:58:04 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.3) Gecko/20120306 Thunderbird/10.0.3

[CC'ing qemu-ppc]

On 06/14/2012 05:52 PM, Richard W.M. Jones wrote:
I found last week that qemu-system-ppc64 (from git) hangs occasionally
under load, and I have a reproducer for it now.  Unfortunately the
reproducer really takes a long time to run -- usually I can get a hang
in under 12 hours.

Here is the reproducer case:



(1) Verified by one other person (other than me).  Happens on both
     ppc64 and x86-64 host.

(2) Happens with both Fedora guest kernel 3.3.4-5.fc17.ppc64 and kernel
     3.5.0 that I compiled myself.  The test case above contains 3.3.4-5.

(3) Seems to be a problem in qemu, not the guest.  The reason I think
     this is because I tried to capture a backtrace of the hang using
     remote gdb, but gdb just hung when trying to connect to qemu
     (gdb connects fine before the bug happens).

(4) Judging by guest messages, appears to be happening when writing
     to the disk.

Can you please try to see if you can repdudice this using vscsi / vio instead of virtio? I couldn't quite see why vio would be any more stable than virtio though ...

Also, could you please try and see if it works reliably using KVM? Maybe we're just encountering some TCG breakage here.


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