net: sched: extend action ops with put_dev callback

As a preparation for removing dependency on rtnl lock from rules update
path, all users of shared objects must take reference while working with
them.

Extend action ops with put_dev() API to be used on net device returned by
get_dev().

Modify mirred action (only action that implements get_dev callback):
- Take reference to net device in get_dev.
- Implement put_dev API that releases reference to net device.
Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/act_api.h

@@ -101,6 +101,7 @@ struct tc_action_ops {
 	void	(*stats_update)(struct tc_action *, u64, u32, u64);
 	size_t  (*get_fill_size)(const struct tc_action *act);
 	struct net_device *(*get_dev)(const struct tc_action *a);
+	void	(*put_dev)(struct net_device *dev);
 	int     (*delete)(struct net *net, u32 index);
 };
 

net/sched/act_mirred.c

@@ -358,8 +358,17 @@ static struct notifier_block mirred_device_notifier = {
 static struct net_device *tcf_mirred_get_dev(const struct tc_action *a)
 {
 	struct tcf_mirred *m = to_mirred(a);
+	struct net_device *dev = rtnl_dereference(m->tcfm_dev);
+
+	if (dev)
+		dev_hold(dev);
 
-	return rtnl_dereference(m->tcfm_dev);
+	return dev;
+}
+
+static void tcf_mirred_put_dev(struct net_device *dev)
+{
+	dev_put(dev);
 }
 
 static int tcf_mirred_delete(struct net *net, u32 index)
@@ -382,6 +391,7 @@ static struct tc_action_ops act_mirred_ops = {
 	.lookup		=	tcf_mirred_search,
 	.size		=	sizeof(struct tcf_mirred),
 	.get_dev	=	tcf_mirred_get_dev,
+	.put_dev	=	tcf_mirred_put_dev,
 	.delete		=	tcf_mirred_delete,
 };
 

net/sched/cls_api.c

@@ -2176,6 +2176,7 @@ static int tc_exts_setup_cb_egdev_call(struct tcf_exts *exts,
 		if (!dev)
 			continue;
 		ret = tc_setup_cb_egdev_call(dev, type, type_data, err_stop);
+		a->ops->put_dev(dev);
 		if (ret < 0)
 			return ret;
 		ok_count += ret;