net/sched: cls_api: conditional notification of events

As of today tc-filter/chain events are unconditionally built and sent to
RTNLGRP_TC. As with the introduction of rtnl_notify_needed we can check
before-hand if they are really needed. This will help to alleviate
system pressure when filters are concurrently added without the rtnl
lock as in tc-flower.
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Pedro Tammela <pctammela@mojatatu.com>
Link: https://lore.kernel.org/r/20231208192847.714940-8-pctammela@mojatatu.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/sched/cls_api.c

@@ -2052,6 +2052,9 @@ static int tfilter_notify(struct net *net, struct sk_buff *oskb,
 	u32 portid = oskb ? NETLINK_CB(oskb).portid : 0;
 	int err = 0;
 
+	if (!unicast && !rtnl_notify_needed(net, n->nlmsg_flags, RTNLGRP_TC))
+		return 0;
+
 	skb = alloc_skb(NLMSG_GOODSIZE, GFP_KERNEL);
 	if (!skb)
 		return -ENOBUFS;
@@ -2081,6 +2084,9 @@ static int tfilter_del_notify(struct net *net, struct sk_buff *oskb,
 	u32 portid = oskb ? NETLINK_CB(oskb).portid : 0;
 	int err;
 
+	if (!rtnl_notify_needed(net, n->nlmsg_flags, RTNLGRP_TC))
+		return tp->ops->delete(tp, fh, last, rtnl_held, extack);
+
 	skb = alloc_skb(NLMSG_GOODSIZE, GFP_KERNEL);
 	if (!skb)
 		return -ENOBUFS;
@@ -2901,6 +2907,9 @@ static int tc_chain_notify(struct tcf_chain *chain, struct sk_buff *oskb,
 	struct sk_buff *skb;
 	int err = 0;
 
+	if (!unicast && !rtnl_notify_needed(net, flags, RTNLGRP_TC))
+		return 0;
+
 	skb = alloc_skb(NLMSG_GOODSIZE, GFP_KERNEL);
 	if (!skb)
 		return -ENOBUFS;
@@ -2930,6 +2939,9 @@ static int tc_chain_notify_delete(const struct tcf_proto_ops *tmplt_ops,
 	struct net *net = block->net;
 	struct sk_buff *skb;
 
+	if (!rtnl_notify_needed(net, flags, RTNLGRP_TC))
+		return 0;
+
 	skb = alloc_skb(NLMSG_GOODSIZE, GFP_KERNEL);
 	if (!skb)
 		return -ENOBUFS;