From: Vlad Buslov <vladbu@mellanox.com>
Date: Fri, 10 Aug 2018 20:51:42 +0300
Subject: net: sched: act_csum: remove dependency on rtnl lock
Patch-mainline: v4.19-rc1
Git-commit: b6a2b971c0b00253197682fbdf1c55fc0e2610a4
References: bsc#1109837

Use tcf lock to protect csum action struct private data from concurrent
modification in init and dump. Use rcu swap operation to reassign params
pointer under protection of tcf lock. (old params value is not used by
init, so there is no need of standalone rcu dereference step)

Remove rtnl assertion that is no longer necessary.

Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 net/sched/act_csum.c |   23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

--- a/net/sched/act_csum.c
+++ b/net/sched/act_csum.c
@@ -50,7 +50,7 @@ static int tcf_csum_init(struct net *net
 			 struct netlink_ext_ack *extack)
 {
 	struct tc_action_net *tn = net_generic(net, csum_net_id);
-	struct tcf_csum_params *params_old, *params_new;
+	struct tcf_csum_params *params_new;
 	struct nlattr *tb[TCA_CSUM_MAX + 1];
 	struct tc_csum *parm;
 	struct tcf_csum *p;
@@ -88,20 +88,22 @@ static int tcf_csum_init(struct net *net
 	}
 
 	p = to_tcf_csum(*a);
-	ASSERT_RTNL();
 
 	params_new = kzalloc(sizeof(*params_new), GFP_KERNEL);
 	if (unlikely(!params_new)) {
 		tcf_idr_release(*a, bind);
 		return -ENOMEM;
 	}
-	params_old = rtnl_dereference(p->params);
+	params_new->update_flags = parm->update_flags;
 
+	spin_lock(&p->tcf_lock);
 	p->tcf_action = parm->action;
-	params_new->update_flags = parm->update_flags;
-	rcu_assign_pointer(p->params, params_new);
-	if (params_old)
-		kfree_rcu(params_old, rcu);
+	rcu_swap_protected(p->params, params_new,
+			   lockdep_is_held(&p->tcf_lock));
+	spin_unlock(&p->tcf_lock);
+
+	if (params_new)
+		kfree_rcu(params_new, rcu);
 
 	if (ret == ACT_P_CREATED)
 		tcf_idr_insert(tn, *a);
@@ -602,7 +604,10 @@ static int tcf_csum_dump(struct sk_buff
 	};
 	struct tcf_t t;
 
-	params = rtnl_dereference(p->params);
+	spin_lock(&p->tcf_lock);
+	params = rcu_dereference_protected(p->params,
+					   lockdep_is_held(&p->tcf_lock));
+	opt.action = p->tcf_action;
 	opt.update_flags = params->update_flags;
 
 	if (nla_put(skb, TCA_CSUM_PARMS, sizeof(opt), &opt))
@@ -611,10 +616,12 @@ static int tcf_csum_dump(struct sk_buff
 	tcf_tm_dump(&t, &p->tcf_tm);
 	if (nla_put_64bit(skb, TCA_CSUM_TM, sizeof(t), &t, TCA_CSUM_PAD))
 		goto nla_put_failure;
+	spin_unlock(&p->tcf_lock);
 
 	return skb->len;
 
 nla_put_failure:
+	spin_unlock(&p->tcf_lock);
 	nlmsg_trim(skb, b);
 	return -1;
 }