releases/3.2.69/virtio_console-avoid-config-access-from-irq.patch

From: "Michael S. Tsirkin" <mst@redhat.com>
Date: Thu, 5 Mar 2015 10:45:49 +1030
Subject: virtio_console: avoid config access from irq

commit eeb8a7e8bb123e84daeef84f5a2eab99ad2839a2 upstream.

when multiport is off, virtio console invokes config access from irq
context, config access is blocking on s390.
Fix this up by scheduling work from config irq - similar to what we do
for multiport configs.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
[bwh: Backported to 3.2:
 - Adjust context
 - Drop changes to virtcons_freeze()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 drivers/char/virtio_console.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -124,6 +124,7 @@ struct ports_device {
 	 * notification
 	 */
 	struct work_struct control_work;
+	struct work_struct config_work;
 
 	struct list_head ports;
 
@@ -1556,10 +1557,21 @@ static void config_intr(struct virtio_de
 
 	portdev = vdev->priv;
 
+	if (!use_multiport(portdev))
+		schedule_work(&portdev->config_work);
+}
+
+static void config_work_handler(struct work_struct *work)
+{
+	struct ports_device *portdev;
+
+	portdev = container_of(work, struct ports_device, control_work);
 	if (!use_multiport(portdev)) {
+		struct virtio_device *vdev;
 		struct port *port;
 		u16 rows, cols;
 
+		vdev = portdev->vdev;
 		vdev->config->get(vdev,
 				  offsetof(struct virtio_console_config, cols),
 				  &cols, sizeof(u16));
@@ -1731,6 +1743,8 @@ static int __devinit virtcons_probe(stru
 	spin_lock_init(&portdev->ports_lock);
 	INIT_LIST_HEAD(&portdev->ports);
 
+	INIT_WORK(&portdev->config_work, &config_work_handler);
+
 	if (multiport) {
 		unsigned int nr_added_bufs;
 
@@ -1806,6 +1820,8 @@ static void virtcons_remove(struct virti
 	/* Finish up work that's lined up */
 	if (use_multiport(portdev))
 		cancel_work_sync(&portdev->control_work);
+	else
+		cancel_work_sync(&portdev->config_work);
 
 	list_for_each_entry_safe(port, port2, &portdev->ports, list)
 		unplug_port(port);