[PATCH net-next v2 13/15] net: sched: act_mirred: remove dependency on rtnl lock

[Vlad Buslov <vladbu@mellanox.com>]

Re-introduce mirred list spinlock, that was removed some time ago, in order
to protect it from concurrent modifications, instead of relying on rtnl
lock.

Use tcf spinlock to protect mirred action private data from concurrent
modification in init and dump. Rearrange access to mirred data in order to
be performed only while holding the lock.

Rearrange net dev access to always hold reference while working with it,
instead of relying on rntl lock.

Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
---
 net/sched/act_mirred.c | 78 +++++++++++++++++++++++++++++++++-----------------
 1 file changed, 51 insertions(+), 27 deletions(-)

diff --git a/net/sched/act_mirred.c b/net/sched/act_mirred.c
index 7a045cc7fe3b..327be257033d 100644
--- a/net/sched/act_mirred.c
+++ b/net/sched/act_mirred.c
@@ -30,6 +30,7 @@
 #include <net/tc_act/tc_mirred.h>
 
 static LIST_HEAD(mirred_list);
+static DEFINE_SPINLOCK(mirred_list_lock);
 
 static bool tcf_mirred_is_act_redirect(int action)
 {
@@ -62,13 +63,23 @@ static bool tcf_mirred_can_reinsert(int action)
 	return false;
 }
 
+static struct net_device *tcf_mirred_dev_dereference(struct tcf_mirred *m)
+{
+	return rcu_dereference_protected(m->tcfm_dev,
+					 lockdep_is_held(&m->tcf_lock));
+}
+
 static void tcf_mirred_release(struct tc_action *a)
 {
 	struct tcf_mirred *m = to_mirred(a);
 	struct net_device *dev;
 
+	spin_lock(&mirred_list_lock);
 	list_del(&m->tcfm_list);
-	dev = rtnl_dereference(m->tcfm_dev);
+	spin_unlock(&mirred_list_lock);
+
+	/* last reference to action, no need to lock */
+	dev = rcu_dereference_protected(m->tcfm_dev, 1);
 	if (dev)
 		dev_put(dev);
 }
@@ -128,22 +139,9 @@ static int tcf_mirred_init(struct net *net, struct nlattr *nla,
 		NL_SET_ERR_MSG_MOD(extack, "Unknown mirred option");
 		return -EINVAL;
 	}
-	if (parm->ifindex) {
-		dev = __dev_get_by_index(net, parm->ifindex);
-		if (dev == NULL) {
-			if (exists)
-				tcf_idr_release(*a, bind);
-			else
-				tcf_idr_cleanup(tn, parm->index);
-			return -ENODEV;
-		}
-		mac_header_xmit = dev_is_mac_header_xmit(dev);
-	} else {
-		dev = NULL;
-	}
 
 	if (!exists) {
-		if (!dev) {
+		if (!parm->ifindex) {
 			tcf_idr_cleanup(tn, parm->index);
 			NL_SET_ERR_MSG_MOD(extack, "Specified device does not exist");
 			return -EINVAL;
@@ -161,19 +159,31 @@ static int tcf_mirred_init(struct net *net, struct nlattr *nla,
 	}
 	m = to_mirred(*a);
 
-	ASSERT_RTNL();
+	spin_lock(&m->tcf_lock);
 	m->tcf_action = parm->action;
 	m->tcfm_eaction = parm->eaction;
-	if (dev != NULL) {
-		if (ret != ACT_P_CREATED)
-			dev_put(rcu_dereference_protected(m->tcfm_dev, 1));
-		dev_hold(dev);
-		rcu_assign_pointer(m->tcfm_dev, dev);
+
+	if (parm->ifindex) {
+		dev = dev_get_by_index(net, parm->ifindex);
+		if (!dev) {
+			spin_unlock(&m->tcf_lock);
+			tcf_idr_release(*a, bind);
+			return -ENODEV;
+		}
+		mac_header_xmit = dev_is_mac_header_xmit(dev);
+		rcu_swap_protected(m->tcfm_dev, dev,
+				   lockdep_is_held(&m->tcf_lock));
+		if (dev)
+			dev_put(dev);
 		m->tcfm_mac_header_xmit = mac_header_xmit;
 	}
+	spin_unlock(&m->tcf_lock);
 
 	if (ret == ACT_P_CREATED) {
+		spin_lock(&mirred_list_lock);
 		list_add(&m->tcfm_list, &mirred_list);
+		spin_unlock(&mirred_list_lock);
+
 		tcf_idr_insert(tn, *a);
 	}
 
@@ -287,26 +297,33 @@ static int tcf_mirred_dump(struct sk_buff *skb, struct tc_action *a, int bind,
 {
 	unsigned char *b = skb_tail_pointer(skb);
 	struct tcf_mirred *m = to_mirred(a);
-	struct net_device *dev = rtnl_dereference(m->tcfm_dev);
 	struct tc_mirred opt = {
 		.index   = m->tcf_index,
-		.action  = m->tcf_action,
 		.refcnt  = refcount_read(&m->tcf_refcnt) - ref,
 		.bindcnt = atomic_read(&m->tcf_bindcnt) - bind,
-		.eaction = m->tcfm_eaction,
-		.ifindex = dev ? dev->ifindex : 0,
 	};
+	struct net_device *dev;
 	struct tcf_t t;
 
+	spin_lock(&m->tcf_lock);
+	opt.action = m->tcf_action;
+	opt.eaction = m->tcfm_eaction;
+	dev = tcf_mirred_dev_dereference(m);
+	if (dev)
+		opt.ifindex = dev->ifindex;
+
 	if (nla_put(skb, TCA_MIRRED_PARMS, sizeof(opt), &opt))
 		goto nla_put_failure;
 
 	tcf_tm_dump(&t, &m->tcf_tm);
 	if (nla_put_64bit(skb, TCA_MIRRED_TM, sizeof(t), &t, TCA_MIRRED_PAD))
 		goto nla_put_failure;
+	spin_unlock(&m->tcf_lock);
+
 	return skb->len;
 
 nla_put_failure:
+	spin_unlock(&m->tcf_lock);
 	nlmsg_trim(skb, b);
 	return -1;
 }
@@ -337,15 +354,19 @@ static int mirred_device_event(struct notifier_block *unused,
 
 	ASSERT_RTNL();
 	if (event == NETDEV_UNREGISTER) {
+		spin_lock(&mirred_list_lock);
 		list_for_each_entry(m, &mirred_list, tcfm_list) {
-			if (rcu_access_pointer(m->tcfm_dev) == dev) {
+			spin_lock(&m->tcf_lock);
+			if (tcf_mirred_dev_dereference(m) == dev) {
 				dev_put(dev);
 				/* Note : no rcu grace period necessary, as
 				 * net_device are already rcu protected.
 				 */
 				RCU_INIT_POINTER(m->tcfm_dev, NULL);
 			}
+			spin_unlock(&m->tcf_lock);
 		}
+		spin_unlock(&mirred_list_lock);
 	}
 
 	return NOTIFY_DONE;
@@ -358,10 +379,13 @@ 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);
+	struct net_device *dev;
 
+	rcu_read_lock();
+	dev = rcu_dereference(m->tcfm_dev);
 	if (dev)
 		dev_hold(dev);
+	rcu_read_unlock();
 
 	return dev;
 }
-- 
2.7.5