Re: [Qemu-devel] [PATCH 5/8] virtio-blk: fix "disabled data plane" mode

[Christian Borntraeger]

On 03/09/2016 02:02 PM, Christian Borntraeger wrote:
> On 03/09/2016 01:55 PM, Paolo Bonzini wrote:
>>
>>
>> On 09/03/2016 13:21, Christian Borntraeger wrote:
>>> I have some random crashes at startup 
>>>                 
>>>                 Stack trace of thread 48326:
>>>                 #0  0x000002aa2e0cce46 bdrv_co_do_rw (qemu-system-s390x)
>>>                 #1  0x000002aa2e159e8e coroutine_trampoline 
>>> (qemu-system-s390x)
>>>                 #2  0x000003ffbc35150a __makecontext_ret (libc.so.6)
>>>
>>>
>>> that I was able to bisect.
>>> commit 2906cddfecff21af20eedab43288b485a679f9ac does crash regularly, 
>>> 2906cddfecff21af20eedab43288b485a679f9ac^ does not.
>>>
>>> I will try to find somebody that looks into that - unless you have an idea.
>>
>> The only random idea is to move
>>
>>     vblk->dataplane_started = true
>>
>> to the beginning of virtio_blk_data_plane_start rather than the end.
>>
>> Paolo
>>
> 
> Indeed
> 
> diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
> index 36f3d2b..1908d59 100644
> --- a/hw/block/dataplane/virtio-blk.c
> +++ b/hw/block/dataplane/virtio-blk.c
> @@ -195,6 +195,7 @@ void virtio_blk_data_plane_start(VirtIOBlockDataPlane *s)
>      if (vblk->dataplane_started || s->starting) {
>          return;
>      }
> +    vblk->dataplane_started = true;
>  
>      s->starting = true;
>      s->vq = virtio_get_queue(s->vdev, 0);
> @@ -235,7 +236,6 @@ void virtio_blk_data_plane_start(VirtIOBlockDataPlane *s)
>    fail_guest_notifiers:
>      s->disabled = true;
>      s->starting = false;
> -    vblk->dataplane_started = true;
>  }
>  
>  /* Context: QEMU global mutex held */
> 
> seems to fix the issue. 

Hmmm, no another crash, just seems to happen less often.