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Subject[PATCH 4.19 43/91] qmi_wwan: avoid RCU stalls on device disconnect when in QMAP mode
Date
[ Upstream commit a8fdde1cb830e560208af42b6c10750137f53eb3 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/usb/qmi_wwan.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/net/usb/qmi_wwan.c b/drivers/net/usb/qmi_wwan.c
index 090227118d3d..44ada5c38756 100644
--- a/drivers/net/usb/qmi_wwan.c
+++ b/drivers/net/usb/qmi_wwan.c
@@ -247,13 +247,14 @@ static int qmimux_register_device(struct net_device *real_dev, u8 mux_id)
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;

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);
@@ -424,7 +425,7 @@ 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;
@@ -1434,6 +1435,7 @@ 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)
@@ -1446,8 +1448,9 @@ 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;
}
--
2.20.1


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