Linux Virtualization - Mar 2015 - [PATCH] virtio_console: avoid config access from irq

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 at redhat.com>
---

Applies on top of "virtio_console: init work unconditionally"
that I sent previously.

 drivers/char/virtio_console.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index def736d..72d7028 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -142,6 +142,7 @@ struct ports_device {
 	 * notification
 	 */
 	struct work_struct control_work;
+	struct work_struct config_work;
 
 	struct list_head ports;
 
@@ -1837,10 +1838,21 @@ static void config_intr(struct virtio_device *vdev)
 
 	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;
 		virtio_cread(vdev, struct virtio_console_config, cols, &cols);
 		virtio_cread(vdev, struct virtio_console_config, rows, &rows);
 
@@ -2040,6 +2052,7 @@ static int virtcons_probe(struct virtio_device *vdev)
 
 	virtio_device_ready(portdev->vdev);
 
+	INIT_WORK(&portdev->config_work, &config_work_handler);
 	INIT_WORK(&portdev->control_work, &control_work_handler);
 
 	if (multiport) {
@@ -2114,6 +2127,8 @@ static void virtcons_remove(struct virtio_device *vdev)
 	/* 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);
@@ -2165,6 +2180,7 @@ static int virtcons_freeze(struct virtio_device *vdev)
 
 	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.
-- 
MST

On (Sat) 28 Feb 2015 [18:42:25], Michael S. Tsirkin
wrote:
> 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 at redhat.com>
Reviewed-by: Amit Shah <amit.shah at redhat.com>

		Amit

Amit Shah <amit.shah at redhat.com> writes:
> On (Sat) 28 Feb 2015 [18:42:25], Michael S. Tsirkin wrote:
>> 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 at redhat.com>
>
> Reviewed-by: Amit Shah <amit.shah at redhat.com>
Applied, thanks.

Should these be CC: stable?

Cheers,
Rusty.