Re: Random guest crashes since 5c34d002dcc7 ("virtio_pci: use shared interrupts for virtqueues")

[Mike Galbraith]

On Mon, 2017-03-27 at 20:18 +0200, Mike Galbraith wrote:

> BTW, WRT RT woes with $subject, I tried booting a generic kernel with
> threadirqs, and bingo, same deal, just a bit more painful than for RT,
> where there's no watchdog moaning accompanying the (preemptible) spin.

BTW++: the last hunk of this bandaid may be a bug fix.  With only the
first two, box tried to use uninitialized stuff on hibernate, went
boom.  Looks like that may be possible without help from me.

--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -2058,7 +2058,7 @@ static int virtcons_probe(struct virtio_
 	portdev->max_nr_ports = 1;
 
 	/* Don't test MULTIPORT at all if we're rproc: not a valid feature! */
-	if (!is_rproc_serial(vdev) &&
+	if (!is_rproc_serial(vdev) && !IS_ENABLED(CONFIG_IRQ_FORCED_THREADING) &&
 	    virtio_cread_feature(vdev, VIRTIO_CONSOLE_F_MULTIPORT,
 				 struct virtio_console_config, max_nr_ports,
 				 &portdev->max_nr_ports) == 0) {
@@ -2179,7 +2179,9 @@ static struct virtio_device_id id_table[
 
 static unsigned int features[] = {
 	VIRTIO_CONSOLE_F_SIZE,
+#ifndef CONFIG_IRQ_FORCED_THREADING
 	VIRTIO_CONSOLE_F_MULTIPORT,
+#endif
 };
 
 static struct virtio_device_id rproc_serial_id_table[] = {
@@ -2202,14 +2204,16 @@ static int virtcons_freeze(struct virtio
 
 	vdev->config->reset(vdev);
 
-	virtqueue_disable_cb(portdev->c_ivq);
+	if (use_multiport(portdev))
+		virtqueue_disable_cb(portdev->c_ivq);
 	cancel_work_sync(&portdev->control_work);
 	cancel_work_sync(&portdev->config_work);
 	/*
 	 * Once more: if control_work_handler() was running, it would
 	 * enable the cb as the last step.
 	 */
-	virtqueue_disable_cb(portdev->c_ivq);
+	if (use_multiport(portdev))
+		virtqueue_disable_cb(portdev->c_ivq);
 	remove_controlq_data(portdev);
 
 	list_for_each_entry(port, &portdev->ports, list) {