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From: tu bo <tubo@linux.vnet.ibm.com>
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Date: Thu, 17 Mar 2016 19:03:10 +0800
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Subject: Re: [Qemu-devel] [PATCH 0/4] Tweaks around virtio-blk start/stop
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To: Fam Zheng <famz@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, qemu-block@nongnu.org, "Michael S. Tsirkin" <mst@redhat.com>, qemu-devel@nongnu.org, Christian Borntraeger <borntraeger@de.ibm.com>, Stefan Hajnoczi <stefanha@redhat.com>, cornelia.huck@de.ibm.com


On 03/17/2016 08:39 AM, Fam Zheng wrote:
> On Wed, 03/16 14:45, Paolo Bonzini wrote:
>>
>>
>> On 16/03/2016 14:38, Christian Borntraeger wrote:
>>>> If you just remove the calls to virtio_queue_host_notifier_read, here
>>>> and in virtio_queue_aio_set_host_notifier_fd_handler, does it work
>>>> (keeping patches 2-4 in)?
>>>
>>> With these changes and patch 2-4 it does no longer locks up.
>>> I keep it running some hour to check if a crash happens.
>>>
>>> Tu Bo, your setup is currently better suited for reproducing. Can you also check?
>>
>> Great, I'll prepare a patch to virtio then sketching the solution that
>> Conny agreed with.
>>
>> While Fam and I agreed that patch 1 is not required, I'm not sure if the
>> mutex is necessary in the end.
>
> If we can fix this from the virtio_queue_host_notifier_read side, the mutex/BH
> are not necessary; but OTOH the mutex does catch such bugs, so maybe it's good
> to have it. I'm not sure about the BH.
>
> And on a hindsight I realize we don't want patches 2-3 too. Actually the
> begin/end pair won't work as expected because of the blk_set_aio_context.
>
> Let's hold on this series.
>
>>
>> So if Tu Bo can check without the virtio_queue_host_notifier_read calls,
>> and both with/without Fam's patches, it would be great.
>
> Tu Bo, only with/withoug patch 4, if you want to check. Sorry for the noise.
>
1. without the virtio_queue_host_notifier_read calls,  without patch 4

crash happens very often,

(gdb) bt
#0  bdrv_co_do_rw (opaque=0x0) at block/io.c:2172
#1  0x000002aa165da37e in coroutine_trampoline (i0=<optimized out>, 
i1=1812051552) at util/coroutine-ucontext.c:79
#2  0x000003ff7dd5150a in __makecontext_ret () from /lib64/libc.so.6


2. without the virtio_queue_host_notifier_read calls, with patch 4

crash happens very often,

(gdb) bt
#0  bdrv_co_do_rw (opaque=0x0) at block/io.c:2172
#1  0x000002aa39dda43e in coroutine_trampoline (i0=<optimized out>, 
i1=-1677715600) at util/coroutine-ucontext.c:79
#2  0x000003ffab6d150a in __makecontext_ret () from /lib64/libc.so.6


> Thanks,
> Fam
>