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Subject[PATCH 3.16.y-ckt 015/144] virtio_console: avoid config access from irq
Date
3.16.7-ckt10 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: "Michael S. Tsirkin" <mst@redhat.com>

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>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
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 5f6dce6c20fb..73294b270b93 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;

@@ -1832,10 +1833,21 @@ 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);

@@ -2024,6 +2036,7 @@ static int virtcons_probe(struct virtio_device *vdev)
spin_lock_init(&portdev->ports_lock);
INIT_LIST_HEAD(&portdev->ports);

+ INIT_WORK(&portdev->config_work, &config_work_handler);
INIT_WORK(&portdev->control_work, &control_work_handler);

if (multiport) {
@@ -2098,6 +2111,8 @@ 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);
@@ -2149,6 +2164,7 @@ 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.

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