Re: [Qemu-devel] [PATCH 0/4] Tweaks around virtio-blk start/stop

[tu bo <tubo@linux.vnet.ibm.com>]

Hi Fam:

On 03/21/2016 06:57 PM, Fam Zheng wrote:
> On Thu, 03/17 19:03, tu bo wrote:
>>
>> 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
>>
>>
>
> Tu Bo,
>
> Could you help test this patch (on top of master, without patch 4)?
>
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 08275a9..47f8043 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -1098,7 +1098,14 @@ void virtio_queue_notify_vq(VirtQueue *vq)
>
>   void virtio_queue_notify(VirtIODevice *vdev, int n)
>   {
> -    virtio_queue_notify_vq(&vdev->vq[n]);
> +    VirtQueue *vq = &vdev->vq[n];
> +    EventNotifier *n;
> +    n = virtio_queue_get_host_notifier(vq);
> +    if (n) {
> +        event_notifier_set(n);
> +    } else {
> +        virtio_queue_notify_vq(vq);
> +    }
>   }
>
>   uint16_t virtio_queue_vector(VirtIODevice *vdev, int n)
>
>

I got a build error as below,

/BUILD/qemu-2.5.50/hw/virtio/virtio.c: In function 'virtio_queue_notify':
/BUILD/qemu-2.5.50/hw/virtio/virtio.c:1102:20: error: 'n' redeclared as 
different kind of symbol
      EventNotifier *n;
                     ^
/BUILD/qemu-2.5.50/hw/virtio/virtio.c:1099:50: note: previous definition 
of 'n' was here
  void virtio_queue_notify(VirtIODevice *vdev, int n)


Then I did some change for your patch as below,
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 08275a9..a10da39 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -1098,7 +1098,14 @@ void virtio_queue_notify_vq(VirtQueue *vq)

  void virtio_queue_notify(VirtIODevice *vdev, int n)
  {
-    virtio_queue_notify_vq(&vdev->vq[n]);
+    VirtQueue *vq = &vdev->vq[n];
+    EventNotifier *en;
+    en = virtio_queue_get_host_notifier(vq);
+    if (en) {
+        event_notifier_set(en);
+    } else {
+        virtio_queue_notify_vq(vq);
+    }
  }

  uint16_t virtio_queue_vector(VirtIODevice *vdev, int n)

With qemu master + modified patch above(without patch 4, without Conny's 
patches), I did NOT get crash so far.  thanks



>