Re: [Qemu-devel] [RFC] block io lost in the guest , possible related to qemu?

[Alexey Zaytsev]

Hey.

I very much doubt this commit could be causing the problem, as qemu
would never set wrong request type in the first place. You can easily
check by either reverting it, or adding a printk() before
virtio_blk_req_complete(VIRTIO_BLK_S_UNSUPP).

On Mon, Oct 28, 2013 at 10:15 AM, Jack Wang <address@hidden> wrote:
> Hello Kevin & Stefan
>
> Any comments or wild guess about the bug?
>
> Regards,
> Jack
>
> On 10/25/2013 05:01 PM, Jack Wang wrote:
>> Hi Experts,
>>
>> We've seen guest block io lost in a VM.any response will be helpful
>>
>> environment is:
>> guest os: Ubuntu 1304
>> running busy database workload with xfs on a disk export with virtio-blk
>>
>> the exported vdb has very high infight io over 300. Some times later a
>> lot io process in D state, looks a lot requests is lost in below storage
>> stack.
>>
>> We're use qemu-kvm 1.0, host kernel 3.4.51
>>
>> In qemu log of virtio-blk.c
>> I found below commit, I wonder is it possible the workload generate some
>> unknown reqests to qemu that lost in virtio_blk_handle_read?
>> I do some fio test myself, I cann't generate so call unknown request type.
>>
>> Any response will be helpful.
>>
>> Jack
>>
>>
>> commit 9e72c45033770b81b536ac6091e91807247cc25a
>> Author: Alexey Zaytsev <address@hidden>
>> Date:   Thu Dec 13 09:03:43 2012 +0200
>>
>>     virtio-blk: Return UNSUPP for unknown request types
>>
>>     Currently, all unknown requests are treated as VIRTIO_BLK_T_IN
>>
>>     Signed-off-by: Alexey Zaytsev <address@hidden>
>>     Signed-off-by: Stefan Hajnoczi <address@hidden>
>>
>> diff --git a/hw/virtio-blk.c b/hw/virtio-blk.c
>> index 92c745a..df57b35 100644
>> --- a/hw/virtio-blk.c
>> +++ b/hw/virtio-blk.c
>> @@ -398,10 +398,14 @@ static void
>> virtio_blk_handle_request(VirtIOBlockReq *req,
>>          qemu_iovec_init_external(&req->qiov, &req->elem.out_sg[1],
>>                                   req->elem.out_num - 1);
>>          virtio_blk_handle_write(req, mrb);
>> -    } else {
>> +    } else if (type == VIRTIO_BLK_T_IN || type == VIRTIO_BLK_T_BARRIER) {
>> +        /* VIRTIO_BLK_T_IN is 0, so we can't just & it. */
>>          qemu_iovec_init_external(&req->qiov, &req->elem.in_sg[0],
>>                                   req->elem.in_num - 1);
>>          virtio_blk_handle_read(req);
>> +    } else {
>> +        virtio_blk_req_complete(req, VIRTIO_BLK_S_UNSUPP);
>> +        g_free(req);
>>      }
>>  }
>>
>