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.
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