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    Subject[PATCH 3.12 039/155] virtio_console: avoid config access from irq
    Date
    From: "Michael S. Tsirkin" <mst@redhat.com>

    3.12-stable review patch. If anyone has any objections, please let me know.

    ===============

    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: Jiri Slaby <jslaby@suse.cz>
    ---
    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 4d5fcc2d6c9c..f6b96ba57b32 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;

    @@ -1833,10 +1834,21 @@ 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;
    vdev->config->get(vdev,
    offsetof(struct virtio_console_config, cols),
    &cols, sizeof(u16));
    @@ -2030,6 +2042,7 @@ 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) {
    @@ -2104,6 +2117,8 @@ 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);
    @@ -2155,6 +2170,7 @@ 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.
    --
    2.3.4


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