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

[Paolo Bonzini]

On 16/03/2016 12:32, Cornelia Huck wrote:
> On Wed, 16 Mar 2016 12:09:02 +0100
> Paolo Bonzini <address@hidden> wrote:
> 
>> On 16/03/2016 11:49, Christian Borntraeger wrote:
> 
>>> #3  0x00000000800b713e in virtio_blk_data_plane_start (s=0xba232d80) at 
>>> /home/cborntra/REPOS/qemu/hw/block/dataplane/virtio-blk.c:224
>>> #4  0x00000000800b4ea0 in virtio_blk_handle_output (vdev=0xb9eee7e8, 
>>> vq=0xba305270) at /home/cborntra/REPOS/qemu/hw/block/virtio-blk.c:590
>>> #5  0x00000000800ef3dc in virtio_queue_notify_vq (vq=0xba305270) at 
>>> /home/cborntra/REPOS/qemu/hw/virtio/virtio.c:1095
>>> #6  0x00000000800f1c9c in virtio_queue_host_notifier_read (n=0xba3052c8) at 
>>> /home/cborntra/REPOS/qemu/hw/virtio/virtio.c:1785
>>> #7  0x00000000800f1e14 in virtio_queue_set_host_notifier_fd_handler 
>>> (vq=0xba305270, assign=false, set_handler=false) at 
>>> /home/cborntra/REPOS/qemu/hw/virtio/virtio.c:1817
>>> #8  0x0000000080109c50 in virtio_ccw_set_guest2host_notifier 
>>> (dev=0xb9eed6a0, n=0, assign=false, set_handler=false) at 
>>> /home/cborntra/REPOS/qemu/hw/s390x/virtio-ccw.c:97
>>> #9  0x0000000080109ef2 in virtio_ccw_stop_ioeventfd (dev=0xb9eed6a0) at 
>>> /home/cborntra/REPOS/qemu/hw/s390x/virtio-ccw.c:154
>>
>> One bug is here: virtio_ccw_stop_ioeventfd, in this case, should pass
>> assign=true to virtio_ccw_set_guest2host_notifier.  (Assuming my
>> understanding of assign=true is correct; I think it means "I'm going to
>> set up another host notifier handler").
> 
> Hm... I copied these semantics from virtio-pci, and they still seem to
> be the same. I wonder why we never saw this on virtio-pci?

Just because we never ran the right tests, probably.  The bug is indeed
in virtio-pci as well (I didn't check mmio).

>> In dataplane, instead, all calls to
>> virtio_queue_set_host_notifier_fd_handler and
>> virtio_queue_aio_set_host_notifier_handler should have assign=true.  The
>> ioeventfd is just being moved from one aiocontext to another.
> 
> How can a transport know where they are called from?

That's a bug in dataplane.  The calls should be changed in
hw/block/dataplane/virtio-blk.c

Paolo