On Tue, 02/27 15:30, Stefan Hajnoczi wrote: > On Fri, Feb 23, 2018 at 04:20:44PM +0800, Fam Zheng wrote: > > On Tue, 02/20 13:10, Stefan Hajnoczi wrote: > > > 1. virtio_scsi_handle_cmd_vq() racing with iothread_stop_all() hits the > > > virtio_scsi_ctx_check() assertion failure because the BDS AioContext > > > has been modified by iothread_stop_all(). > > > > Does this patch fix the issue completely? IIUC virtio_scsi_handle_cmd can > > already be entered at the time of main thread calling > > virtio_scsi_clear_aio(), > > so this race condition still exists: > > > > main thread iothread > > ----------------------------------------------------------------------------- > > vm_shutdown > > ... > > virtio_bus_stop_ioeventfd > > virtio_scsi_dataplane_stop > > aio_poll() > > ... > > > > virtio_scsi_data_plane_handle_cmd() > > aio_context_acquire(s->ctx) > > virtio_scsi_acquire(s).enter > > virtio_scsi_clear_aio() > > aio_context_release(s->ctx) > > virtio_scsi_acquire(s).return > > virtio_scsi_handle_cmd_vq() > > ... > > virtqueue_pop() > > > > Is it possible that the above virtqueue_pop() still returns one element > > that was > > queued before vm_shutdown() was called? > > No, it can't because virtio_scsi_clear_aio() invokes > virtio_queue_host_notifier_aio_read(&vq->host_notifier) to process the > virtqueue. By the time we get back to iothread's > virtio_scsi_data_plane_handle_cmd() the virtqueue is already empty. > > Vcpus have been paused so no additional elements can slip into the > virtqueue.
So there is: static void virtio_queue_host_notifier_aio_read(EventNotifier *n) { VirtQueue *vq = container_of(n, VirtQueue, host_notifier); if (event_notifier_test_and_clear(n)) { virtio_queue_notify_aio_vq(vq); } } Guest kicks after adding an element to VQ, but we check ioeventfd before trying virtqueue_pop(). Is that a problem? If VCPUs are paused after enqueuing but before kicking VQ, the ioeventfd is not set, the virtqueue is not processed here. Fam