Hi, I've added a few commands to vhost-user for virtio-fs and am hitting a deadlock and am trying to figure out what the correct fix is; suggestions welcome.
My setup is: Messages sent over the virtio queues can cause the daemon to need to send a request back to qemu along the slave, and qemu must respond with an OK/error. Lets call this command 'setupmapping'. In my case I'm reading vhost-user commands in one thread and processing the queues in another. That normally works OK My problem: If qemu crashes or quits it stops the queues synchronously at a point when the main loop in qemu wont respond to anything else. However if we're unlucky the daemon has already sent a message to qemu and is waiting for the response; but that response can't arrive because qemu is shutting down. So the queue shutdown request never completes. Then if I kill the daemon forcibly, qemu's handler for the slavefd wakes up and tries to read data - but it's device has gone and it crashes. The trace is: (Where vuf_* is my device and the structure is pretty much the same as the others). vm_state_notify->virtio_set_status->vuf_set_status->vuf_stop->vhost_dev_stop->vhost_virtqueue_stop->vhost_user_get_vring_base->vhost_user_read So it feels like we need to shut down the slave FD when we shut down the device; but it's not clear to me at what level. In some ways it feels like we need a way to get out if this hole even if we shut down one queue synchronously. Is anyone fighting similar cases? Dave -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
