hsr: use hsr_for_each_port_rtnl in hsr_port_get_hsr

hsr_port_get_hsr() iterates over ports using hsr_for_each_port(),
but many of its callers do not hold the required RCU lock.

Switch to hsr_for_each_port_rtnl(), since most callers already hold
the rtnl lock. After review, all callers are covered by either the rtnl
lock or the RCU lock, except hsr_dev_xmit(). Fix this by adding an
RCU read lock there.

Fixes: c5a759117210 ("net/hsr: Use list_head (and rcu) instead of array for slave devices.")
Signed-off-by: Hangbin Liu <[e-mail]>
Reviewed-by: Simon Horman <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Paolo Abeni <[e-mail]>

net/hsr/hsr_device.c

···
 	struct hsr_priv *hsr = netdev_priv(dev);
 	struct hsr_port *master;
 
+	rcu_read_lock();
 	master = hsr_port_get_hsr(hsr, HSR_PT_MASTER);
 	if (master) {
 		skb->dev = master->dev;
···
 		dev_core_stats_tx_dropped_inc(dev);
 		dev_kfree_skb_any(skb);
 	}
+	rcu_read_unlock();
+
 	return NETDEV_TX_OK;
 }
 

net/hsr/hsr_main.c

···
 {
 	struct hsr_port *port;
 
-	hsr_for_each_port(hsr, port)
+	hsr_for_each_port_rtnl(hsr, port)
 		if (port->type == pt)
 			return port;
 	return NULL;