Re: [Qemu-devel] [PATCH 1/1] virtio-blk: fix race on guest notifiers

[Paolo Bonzini]

On 02/03/2017 15:49, Cornelia Huck wrote:
> On Thu,  2 Mar 2017 14:04:22 +0100
> Halil Pasic <address@hidden> wrote:
> 
>> diff --git a/hw/block/dataplane/virtio-blk.c 
>> b/hw/block/dataplane/virtio-blk.c
>> index 5556f0e..13dd14d 100644
>> --- a/hw/block/dataplane/virtio-blk.c
>> +++ b/hw/block/dataplane/virtio-blk.c
>> @@ -258,9 +258,16 @@ void virtio_blk_data_plane_stop(VirtIODevice *vdev)
>>          virtio_queue_aio_set_host_notifier_handler(vq, s->ctx, NULL);
>>      }
>>
>> -    /* Drain and switch bs back to the QEMU main loop */
>> +    /* Drain and switch bs back to the QEMU main loop. After drain, the
>> +     * device will not submit (nor comple) any requests until dataplane
> 
> s/comple/complete/
> 
>> +     * starts again.
>> +     */
>>      blk_set_aio_context(s->conf->conf.blk, qemu_get_aio_context());
>>
>> +    /* Notify guest before the guest notifiers get cleaned up */
>> +    qemu_bh_cancel(s->bh);
>> +    notify_guest_bh(s);
>> +
> 
> Hm... does virtio-scsi dataplane need a similar treatment? Or am I
> missing something?

No, the BH optimization is specific to virtio-blk.  Thanks for the patch
Halil!

Paolo

>>      aio_context_release(s->ctx);
>>
>>      for (i = 0; i < nvqs; i++) {
>