net: transfer rtnl_lock() requirement from ethtool_set_ethtool_phy_ops() to caller

phy_init() and phy_exit() will have to do more stuff under rtnl_lock()
in a future change. Since rtnl_unlock() -> netdev_run_todo() does a lot
of stuff under the hood, it's a pity to lock and unlock the rtnetlink
mutex twice in a row.

Change the calling convention such that the only caller of
ethtool_set_ethtool_phy_ops(), phy_device.c, provides a context where
the rtnl_mutex is already acquired.

Signed-off-by: Vladimir Oltean <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/phy/phy_device.c

···
 #include <linux/phy_led_triggers.h>
 #include <linux/pse-pd/pse.h>
 #include <linux/property.h>
+#include <linux/rtnetlink.h>
 #include <linux/sfp.h>
 #include <linux/skbuff.h>
 #include <linux/slab.h>
···
 {
 	int rc;
 
+	rtnl_lock();
 	ethtool_set_ethtool_phy_ops(&phy_ethtool_phy_ops);
+	rtnl_unlock();
 
 	rc = mdio_bus_init();
 	if (rc)
···
 err_mdio_bus:
 	mdio_bus_exit();
 err_ethtool_phy_ops:
+	rtnl_lock();
 	ethtool_set_ethtool_phy_ops(NULL);
+	rtnl_unlock();
 
 	return rc;
 }
···
 	phy_driver_unregister(&genphy_c45_driver);
 	phy_driver_unregister(&genphy_driver);
 	mdio_bus_exit();
+	rtnl_lock();
 	ethtool_set_ethtool_phy_ops(NULL);
+	rtnl_unlock();
 }
 
 subsys_initcall(phy_init);

net/ethtool/common.c

···
 
 void ethtool_set_ethtool_phy_ops(const struct ethtool_phy_ops *ops)
 {
-	rtnl_lock();
+	ASSERT_RTNL();
 	ethtool_phy_ops = ops;
-	rtnl_unlock();
 }
 EXPORT_SYMBOL_GPL(ethtool_set_ethtool_phy_ops);