From: Vlad Buslov <vladbu@mellanox.com>
Date: Mon, 3 Sep 2018 10:07:15 +0300
Subject: net: sched: act_skbedit: remove dependency on rtnl lock
Patch-mainline: v4.20-rc1
Git-commit: 6d7a8df6dfe4d62335673fb15407d79180a33ea2
References: bsc#1109837

According to the new locking rule, we have to take tcf_lock for both
->init() and ->dump(), as RTNL will be removed.

Use tcf lock to protect skbedit 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 lock assertion that is no longer required.

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_skbedit.c |   23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

--- a/net/sched/act_skbedit.c
+++ b/net/sched/act_skbedit.c
@@ -99,7 +99,7 @@ static int tcf_skbedit_init(struct net *
 			    struct netlink_ext_ack *extack)
 {
 	struct tc_action_net *tn = net_generic(net, skbedit_net_id);
-	struct tcf_skbedit_params *params_old, *params_new;
+	struct tcf_skbedit_params *params_new;
 	struct nlattr *tb[TCA_SKBEDIT_MAX + 1];
 	struct tc_skbedit *parm;
 	struct tcf_skbedit *d;
@@ -187,8 +187,6 @@ static int tcf_skbedit_init(struct net *
 		}
 	}
 
-	ASSERT_RTNL();
-
 	params_new = kzalloc(sizeof(*params_new), GFP_KERNEL);
 	if (unlikely(!params_new)) {
 		if (ret == ACT_P_CREATED)
@@ -210,11 +208,13 @@ static int tcf_skbedit_init(struct net *
 	if (flags & SKBEDIT_F_MASK)
 		params_new->mask = *mask;
 
+	spin_lock_bh(&d->tcf_lock);
 	d->tcf_action = parm->action;
-	params_old = rtnl_dereference(d->params);
-	rcu_assign_pointer(d->params, params_new);
-	if (params_old)
-		kfree_rcu(params_old, rcu);
+	rcu_swap_protected(d->params, params_new,
+			   lockdep_is_held(&d->tcf_lock));
+	spin_unlock_bh(&d->tcf_lock);
+	if (params_new)
+		kfree_rcu(params_new, rcu);
 
 	if (ret == ACT_P_CREATED)
 		tcf_idr_insert(tn, *a);
@@ -231,12 +231,14 @@ static int tcf_skbedit_dump(struct sk_bu
 		.index   = d->tcf_index,
 		.refcnt  = refcount_read(&d->tcf_refcnt) - ref,
 		.bindcnt = atomic_read(&d->tcf_bindcnt) - bind,
-		.action  = d->tcf_action,
 	};
 	u64 pure_flags = 0;
 	struct tcf_t t;
 
-	params = rtnl_dereference(d->params);
+	spin_lock_bh(&d->tcf_lock);
+	params = rcu_dereference_protected(d->params,
+					   lockdep_is_held(&d->tcf_lock));
+	opt.action = d->tcf_action;
 
 	if (nla_put(skb, TCA_SKBEDIT_PARMS, sizeof(opt), &opt))
 		goto nla_put_failure;
@@ -264,9 +266,12 @@ static int tcf_skbedit_dump(struct sk_bu
 	tcf_tm_dump(&t, &d->tcf_tm);
 	if (nla_put_64bit(skb, TCA_SKBEDIT_TM, sizeof(t), &t, TCA_SKBEDIT_PAD))
 		goto nla_put_failure;
+	spin_unlock_bh(&d->tcf_lock);
+
 	return skb->len;
 
 nla_put_failure:
+	spin_unlock_bh(&d->tcf_lock);
 	nlmsg_trim(skb, b);
 	return -1;
 }