qmi_wwan: avoid RCU stalls on device disconnect when in QMAP mode

Switch qmimux_unregister_device() and qmi_wwan_disconnect() to
use unregister_netdevice_queue() and unregister_netdevice_many()
instead of unregister_netdevice(). This avoids RCU stalls which
have been observed on device disconnect in certain setups otherwise.

Fixes: c6adf77953bc ("net: usb: qmi_wwan: add qmap mux protocol support")
Cc: Daniele Palmas <dnlplm@gmail.com>
Signed-off-by: Reinhard Speyerer <rspmn@arcor.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 4 deletions

diff --git a/drivers/net/usb/qmi_wwan.c b/drivers/net/usb/qmi_wwan.c
index b0a96459621f..c6fbc2a2a785 100644
--- a/drivers/net/usb/qmi_wwan.c
+++ b/drivers/net/usb/qmi_wwan.c
@@ -312,14 +312,15 @@ out_free_newdev:
         return err;
 }
 
-static void qmimux_unregister_device(struct net_device *dev)
+static void qmimux_unregister_device(struct net_device *dev,
+                                     struct list_head *head)
 {
         struct qmimux_priv *priv = netdev_priv(dev);
         struct net_device *real_dev = priv->real_dev;
 
         free_percpu(priv->stats64);
         netdev_upper_dev_unlink(real_dev, dev);
-        unregister_netdevice(dev);
+        unregister_netdevice_queue(dev, head);
 
         /* Get rid of the reference to real_dev */
         dev_put(real_dev);
@@ -490,7 +491,7 @@ static ssize_t del_mux_store(struct device *d,  struct device_attribute *attr, c
                 ret = -EINVAL;
                 goto err;
         }
-        qmimux_unregister_device(del_dev);
+        qmimux_unregister_device(del_dev, NULL);
 
         if (!qmimux_has_slaves(dev))
                 info->flags &= ~QMI_WWAN_FLAG_MUX;
@@ -1500,6 +1501,7 @@ static void qmi_wwan_disconnect(struct usb_interface *intf)
         struct qmi_wwan_state *info;
         struct list_head *iter;
         struct net_device *ldev;
+        LIST_HEAD(list);
 
         /* called twice if separate control and data intf */
         if (!dev)
@@ -1512,8 +1514,9 @@ static void qmi_wwan_disconnect(struct usb_interface *intf)
                 }
                 rcu_read_lock();
                 netdev_for_each_upper_dev_rcu(dev->net, ldev, iter)
-                        qmimux_unregister_device(ldev);
+                        qmimux_unregister_device(ldev, &list);
                 rcu_read_unlock();
+                unregister_netdevice_many(&list);
                 rtnl_unlock();
                 info->flags &= ~QMI_WWAN_FLAG_MUX;
         }