Re: [Qemu-block] forward of qemu bug regarding random qemu hangs at shutdown

[Marc Hartmayer]

On Fri, Sep 07, 2018 at 11:34 AM +0200, Kevin Wolf <address@hidden> wrote:
> Am 06.09.2018 um 21:29 hat Christian Borntraeger geschrieben:
>> Kevin,
>>
>> for reference, it seems that his bug report somehow got lost.
>> https://bugs.launchpad.net/qemu/+bug/1788582
>
> That looks... interesting. The reproducer doesn't even seem to use a
> block device, and the backtrace shows a QEMU that is just sitting in the
> main loop waiting for events, not somewhere in the shutdown process
> after exiting the main loop where bdrv_drain_all() would be called. I
> fail to even come up with a theory about any connection between this and
> commit 0f12264e7.
>
> I think we need more information there. Can you set a breakpoint on
> bdrv_drain_all_begin() to see where it's even called? When I start a
> qemu instance without a block device, the first time this is called is
> during shutdown after the mainloop (i.e. after the place where you're
> seeing a hang).

I can try that.

>
> Maybe bisect within the commit that seems to cause the bug, by
> selectively disabling some hunks in it?

If I remove the line(s)

/* Execute pending BHs first (may modify the graph) and check everything
 * else only after the BHs have executed. */
while (aio_poll(qemu_get_aio_context(), false));

in the function 'bdrv_drain_all_poll', then it works.

>
> Kevin
>
--
Kind regards / Beste Grüße
   Marc Hartmayer

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