net_sched: act_skbmod: use RCU in tcf_skbmod_dump()

Also storing tcf_action into struct tcf_skbmod_params
makes sure there is no discrepancy in tcf_skbmod_act().

No longer block BH in tcf_skbmod_init() when acquiring tcf_lock.

Signed-off-by: Eric Dumazet <[e-mail]>
Reviewed-by: Simon Horman <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

include/net/tc_act/tc_skbmod.h

···
 struct tcf_skbmod_params {
 	struct rcu_head	rcu;
 	u64	flags; /*up to 64 types of operations; extend if needed */
+	int	action;
 	u8	eth_dst[ETH_ALEN];
 	u16	eth_type;
 	u8	eth_src[ETH_ALEN];

net/sched/act_skbmod.c

···
 				     struct tcf_result *res)
 {
 	struct tcf_skbmod *d = to_skbmod(a);
-	int action, max_edit_len, err;
 	struct tcf_skbmod_params *p;
+	int max_edit_len, err;
 	u64 flags;
 
 	tcf_lastuse_update(&d->tcf_tm);
 	bstats_update(this_cpu_ptr(d->common.cpu_bstats), skb);
 
-	action = READ_ONCE(d->tcf_action);
-	if (unlikely(action == TC_ACT_SHOT))
+	p = rcu_dereference_bh(d->skbmod_p);
+	if (unlikely(p->action == TC_ACT_SHOT))
 		goto drop;
 
 	max_edit_len = skb_mac_header_len(skb);
-	p = rcu_dereference_bh(d->skbmod_p);
 	flags = p->flags;
 
 	/* tcf_skbmod_init() guarantees "flags" to be one of the following:
···
 		INET_ECN_set_ce(skb);
 
 out:
-	return action;
+	return p->action;
 
 drop:
 	qstats_overlimit_inc(this_cpu_ptr(d->common.cpu_qstats));
···
 	}
 
 	p->flags = lflags;
-
+	p->action = parm->action;
 	if (ovr)
-		spin_lock_bh(&d->tcf_lock);
+		spin_lock(&d->tcf_lock);
 	/* Protected by tcf_lock if overwriting existing action. */
 	goto_ch = tcf_action_set_ctrlact(*a, parm->action, goto_ch);
 	p_old = rcu_dereference_protected(d->skbmod_p, 1);
···
 
 	rcu_assign_pointer(d->skbmod_p, p);
 	if (ovr)
-		spin_unlock_bh(&d->tcf_lock);
+		spin_unlock(&d->tcf_lock);
 
 	if (p_old)
 		kfree_rcu(p_old, rcu);
···
 	opt.index   = d->tcf_index;
 	opt.refcnt  = refcount_read(&d->tcf_refcnt) - ref;
 	opt.bindcnt = atomic_read(&d->tcf_bindcnt) - bind;
-	spin_lock_bh(&d->tcf_lock);
-	opt.action = d->tcf_action;
-	p = rcu_dereference_protected(d->skbmod_p,
-				      lockdep_is_held(&d->tcf_lock));
+	rcu_read_lock();
+	p = rcu_dereference(d->skbmod_p);
+	opt.action = p->action;
 	opt.flags  = p->flags;
 	if (nla_put(skb, TCA_SKBMOD_PARMS, sizeof(opt), &opt))
 		goto nla_put_failure;
···
 	if (nla_put_64bit(skb, TCA_SKBMOD_TM, sizeof(t), &t, TCA_SKBMOD_PAD))
 		goto nla_put_failure;
 
-	spin_unlock_bh(&d->tcf_lock);
+	rcu_read_unlock();
 	return skb->len;
 nla_put_failure:
-	spin_unlock_bh(&d->tcf_lock);
+	rcu_read_unlock();
 	nlmsg_trim(skb, b);
 	return -1;
 }