ipv6 mcast: use in6_dev_put in timer handlers instead of __in6_dev_put

[ Upstream commit 9260d3e1 ]

It is possible for the timer handlers to run after the call to
ipv6_mc_down so use in6_dev_put instead of __in6_dev_put in the
handler function in order to do proper cleanup when the refcnt
reaches 0. Otherwise, the refcnt can reach zero without the
inet6_dev being destroyed and we end up leaking a reference to
the net_device and see messages like the following,

unregister_netdevice: waiting for eth0 to become free. Usage count = 1

Tested on linux-3.4.43.
Signed-off-by: Salam Noureddine <noureddine@aristanetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

net/ipv6/mcast.c

@@ -2158,7 +2158,7 @@ static void mld_gq_timer_expire(unsigned long data)
 
 	idev->mc_gq_running = 0;
 	mld_send_report(idev, NULL);
-	__in6_dev_put(idev);
+	in6_dev_put(idev);
 }
 
 static void mld_ifc_timer_expire(unsigned long data)
@@ -2171,7 +2171,7 @@ static void mld_ifc_timer_expire(unsigned long data)
 		if (idev->mc_ifc_count)
 			mld_ifc_start_timer(idev, idev->mc_maxdelay);
 	}
-	__in6_dev_put(idev);
+	in6_dev_put(idev);
 }
 
 static void mld_ifc_event(struct inet6_dev *idev)