virtio-scsi: reset virtqueue affinity when doing cpu hotplug

Add hot cpu notifier to reset the request virtqueue affinity
when doing cpu hotplug.

Cc: [e-mail]
Signed-off-by: Paolo Bonzini <[e-mail]>
Signed-off-by: Wanlong Gao <[e-mail]>
Reviewed-by: Asias He <[e-mail]>
Signed-off-by: Rusty Russell <[e-mail]>

drivers/scsi/virtio_scsi.c

···
 	/* If the affinity hint is set for virtqueues */
 	bool affinity_hint_set;
 
+	/* CPU hotplug notifier */
+	struct notifier_block nb;
+
 	struct virtio_scsi_vq ctrl_vq;
 	struct virtio_scsi_vq event_vq;
 	struct virtio_scsi_vq req_vqs[];
···
 	put_online_cpus();
 }
 
+static int virtscsi_cpu_callback(struct notifier_block *nfb,
+				 unsigned long action, void *hcpu)
+{
+	struct virtio_scsi *vscsi = container_of(nfb, struct virtio_scsi, nb);
+	switch(action) {
+	case CPU_ONLINE:
+	case CPU_ONLINE_FROZEN:
+	case CPU_DEAD:
+	case CPU_DEAD_FROZEN:
+		__virtscsi_set_affinity(vscsi, true);
+		break;
+	default:
+		break;
+	}
+	return NOTIFY_OK;
+}
+
 static void virtscsi_init_vq(struct virtio_scsi_vq *virtscsi_vq,
 			     struct virtqueue *vq)
 {
···
 	if (err)
 		goto virtscsi_init_failed;
 
+	vscsi->nb.notifier_call = &virtscsi_cpu_callback;
+	err = register_hotcpu_notifier(&vscsi->nb);
+	if (err) {
+		pr_err("registering cpu notifier failed\n");
+		goto scsi_add_host_failed;
+	}
+
 	cmd_per_lun = virtscsi_config_get(vdev, cmd_per_lun) ?: 1;
 	shost->cmd_per_lun = min_t(u32, cmd_per_lun, shost->can_queue);
 	shost->max_sectors = virtscsi_config_get(vdev, max_sectors) ?: 0xFFFF;
···
 		virtscsi_cancel_event_work(vscsi);
 
 	scsi_remove_host(shost);
+
+	unregister_hotcpu_notifier(&vscsi->nb);
 
 	virtscsi_remove_vqs(vdev);
 	scsi_host_put(shost);