linux-kernel - [PATCH 4.4 23/29] xen-netfront: Update features after registering netdev

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Date:   Sat, 11 Apr 2020 14:08:53 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Liam Shepherd <liam@...cer.es>,
        Ross Lagerwall <ross.lagerwall@...rix.com>,
        Juergen Gross <jgross@...e.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Nobuhiro Iwamatsu (CIP)" <nobuhiro1.iwamatsu@...hiba.co.jp>
Subject: [PATCH 4.4 23/29] xen-netfront: Update features after registering netdev

From: Ross Lagerwall <ross.lagerwall@...rix.com>

commit 45c8184c1bed1ca8a7f02918552063a00b909bf5 upstream.

Update the features after calling register_netdev() otherwise the
device features are not set up correctly and it not possible to change
the MTU of the device. After this change, the features reported by
ethtool match the device's features before the commit which introduced
the issue and it is possible to change the device's MTU.

Fixes: f599c64fdf7d ("xen-netfront: Fix race between device setup and open")
Reported-by: Liam Shepherd <liam@...cer.es>
Signed-off-by: Ross Lagerwall <ross.lagerwall@...rix.com>
Reviewed-by: Juergen Gross <jgross@...e.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Nobuhiro Iwamatsu (CIP) <nobuhiro1.iwamatsu@...hiba.co.jp>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/net/xen-netfront.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -1982,10 +1982,6 @@ static int xennet_connect(struct net_dev
 	/* talk_to_netback() sets the correct number of queues */
 	num_queues = dev->real_num_tx_queues;

-	rtnl_lock();
-	netdev_update_features(dev);
-	rtnl_unlock();
-
 	if (dev->reg_state == NETREG_UNINITIALIZED) {
 		err = register_netdev(dev);
 		if (err) {
@@ -1995,6 +1991,10 @@ static int xennet_connect(struct net_dev
 		}
 	}

+	rtnl_lock();
+	netdev_update_features(dev);
+	rtnl_unlock();
+
 	/*
 	 * All public and private state should now be sane.  Get
 	 * ready to start sending and receiving packets and give the driver