On 01/03/2017 17:08, Halil Pasic wrote: > applied I do not see the problem any more. I will most likely > turn this into a patch tomorrow. I would like to give it some more testing and > thinking (see questions below) until tomorrow. > > I should probably cc stable, or?
Yes, please do! > > Q1. For this to work correctly, it seems to me, we need to be sure that > virtio_blk_req_complete can not be happen between the newly added > notify_guest_bh(s); > and > vblk->dataplane_started = false; > becomes visible. How is this ensured? blk_set_aio_context drains the block device, and the event notifiers are not active anymore so draining the block device coincides with the last call to virtio_blk_req_complete. Please add a comment - it's a good observation. > Q2. The virtio_blk_data_plane_stop should be from the thread/context > associated with the main event loop, and with that > vblk->dataplane_started = false too. But I think dataplane_started > may end up being used form a different thread (e.g. req_complete). 1) virtio_queue_aio_set_host_notifier_handler stops the event notifiers 2) virtio_bus_set_host_notifier invokes them one last time before exiting Note that this could call again virtio_queue_notify_vq and hence virtio_device_start_ioeventfd, but dataplane won't be reactivated because vblk->dataplane_started is still true. > How does the sequencing work there and/or is it even important? It is important and not really easy to get right---as shown by the bug you found, in fact. Thanks, Paolo
