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Date: Mon, 07 Dec 2009 16:03:34 +0100
From: Kevin Wolf <kwolf@redhat.com>
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Subject: [Qemu-devel] Re: Endless loop in qcow2_alloc_cluster_offset
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To: Jan Kiszka <jan.kiszka@siemens.com>
Cc: qemu-devel <qemu-devel@nongnu.org>, kvm <kvm@vger.kernel.org>

Am 07.12.2009 15:50, schrieb Jan Kiszka:
> Jan Kiszka wrote:
>> And now it happened again (qemu-kvm head, during kernel installation
>> from network onto local qcow2-disk). Any clever idea how to proceed with
>> this?
>>
>> I could try to run the step in a loop, hopefully retriggering it once in
>> a (likely longer) while. But then we need some good instrumentation first.
>>
> 
> Maybe I'm seeing ghosts, and I don't even have a minimal clue about what
> goes on in the code, but this looks fishy:
> 
> preallocate() invokes qcow2_alloc_cluster_offset() passing &meta, a
> stack variable. It seems that qcow2_alloc_cluster_offset() may insert
> this structure into cluster_allocs and leave it there. So we corrupt the
> queue as soon as preallocate() returns, no?

preallocate() is about metadata preallocation during image creation. It
is only ever run by qemu-img. Apart from that it calls
run_dependent_requests() which removes the request from the list again.

Kevin