[DECnet]: Use RCU locking in dn_rules.c

As per Robert Olsson's patch for ipv4, this is the DECnet
version to keep the code "in step". It changes the list
of rules to use RCU rather than an rwlock.
Inspired-by: Robert Olsson <robert.olsson@its.uu.se>
Signed-off-by: Steven Whitehouse <steve@chygwyn.com>
Signed-off-by: Patrick Caulfield <patrick@tykepenguin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/decnet/dn_rules.c

@@ -27,6 +27,8 @@
 #include <linux/timer.h>
 #include <linux/spinlock.h>
 #include <linux/in_route.h>
+#include <linux/list.h>
+#include <linux/rcupdate.h>
 #include <asm/atomic.h>
 #include <asm/uaccess.h>
 #include <net/neighbour.h>
@@ -39,7 +41,7 @@
 
 struct dn_fib_rule
 {
-	struct dn_fib_rule	*r_next;
+	struct hlist_node	r_hlist;
 	atomic_t		r_clntref;
 	u32			r_preference;
 	unsigned char		r_table;
@@ -58,6 +60,7 @@ struct dn_fib_rule
 	int			r_ifindex;
 	char			r_ifname[IFNAMSIZ];
 	int			r_dead;
+	struct rcu_head		rcu;
 };
 
 static struct dn_fib_rule default_rule = {
@@ -67,18 +70,17 @@ static struct dn_fib_rule default_rule = {
 	.r_action =		RTN_UNICAST
 };
 
-static struct dn_fib_rule *dn_fib_rules = &default_rule;
-static DEFINE_RWLOCK(dn_fib_rules_lock);
-
+static struct hlist_head dn_fib_rules;
 
 int dn_fib_rtm_delrule(struct sk_buff *skb, struct nlmsghdr *nlh, void *arg)
 {
 	struct rtattr **rta = arg;
 	struct rtmsg *rtm = NLMSG_DATA(nlh);
-	struct dn_fib_rule *r, **rp;
+	struct dn_fib_rule *r;
+	struct hlist_node *node;
 	int err = -ESRCH;
 
-	for(rp=&dn_fib_rules; (r=*rp) != NULL; rp = &r->r_next) {
+	hlist_for_each_entry(r, node, &dn_fib_rules, r_hlist) {
 		if ((!rta[RTA_SRC-1] || memcmp(RTA_DATA(rta[RTA_SRC-1]), &r->r_src, 2) == 0) &&
 			rtm->rtm_src_len == r->r_src_len &&
 			rtm->rtm_dst_len == r->r_dst_len &&
@@ -95,10 +97,8 @@ int dn_fib_rtm_delrule(struct sk_buff *skb, struct nlmsghdr *nlh, void *arg)
 			if (r == &default_rule)
 				break;
 
-			write_lock_bh(&dn_fib_rules_lock);
-			*rp = r->r_next;
+			hlist_del_rcu(&r->r_hlist);
 			r->r_dead = 1;
-			write_unlock_bh(&dn_fib_rules_lock);
 			dn_fib_rule_put(r);
 			err = 0;
 			break;
@@ -108,11 +108,17 @@ int dn_fib_rtm_delrule(struct sk_buff *skb, struct nlmsghdr *nlh, void *arg)
 	return err;
 }
 
+static inline void dn_fib_rule_put_rcu(struct rcu_head *head)
+{
+	struct dn_fib_rule *r = container_of(head, struct dn_fib_rule, rcu);
+	kfree(r);
+}
+
 void dn_fib_rule_put(struct dn_fib_rule *r)
 {
 	if (atomic_dec_and_test(&r->r_clntref)) {
 		if (r->r_dead)
-			kfree(r);
+			call_rcu(&r->rcu, dn_fib_rule_put_rcu);
 		else
 			printk(KERN_DEBUG "Attempt to free alive dn_fib_rule\n");
 	}
@@ -123,7 +129,8 @@ int dn_fib_rtm_newrule(struct sk_buff *skb, struct nlmsghdr *nlh, void *arg)
 {
 	struct rtattr **rta = arg;
 	struct rtmsg *rtm = NLMSG_DATA(nlh);
-	struct dn_fib_rule *r, *new_r, **rp;
+	struct dn_fib_rule *r, *new_r, *last = NULL;
+	struct hlist_node *node = NULL;
 	unsigned char table_id;
 
 	if (rtm->rtm_src_len > 16 || rtm->rtm_dst_len > 16)
@@ -149,6 +156,7 @@ int dn_fib_rtm_newrule(struct sk_buff *skb, struct nlmsghdr *nlh, void *arg)
 	if (!new_r)
 		return -ENOMEM;
 	memset(new_r, 0, sizeof(*new_r));
+
 	if (rta[RTA_SRC-1])
 		memcpy(&new_r->r_src, RTA_DATA(rta[RTA_SRC-1]), 2);
 	if (rta[RTA_DST-1])
@@ -179,27 +187,26 @@ int dn_fib_rtm_newrule(struct sk_buff *skb, struct nlmsghdr *nlh, void *arg)
 		}
 	}
 
-	rp = &dn_fib_rules;
+	r = container_of(dn_fib_rules.first, struct dn_fib_rule, r_hlist);
 	if (!new_r->r_preference) {
-		r = dn_fib_rules;
-		if (r && (r = r->r_next) != NULL) {
-			rp = &dn_fib_rules->r_next;
+		if (r && r->r_hlist.next != NULL) {
+			r = container_of(r->r_hlist.next, struct dn_fib_rule, r_hlist);
 			if (r->r_preference)
 				new_r->r_preference = r->r_preference - 1;
 		}
 	}
 
-	while((r=*rp) != NULL) {
+	hlist_for_each_entry(r, node, &dn_fib_rules, r_hlist) {
 		if (r->r_preference > new_r->r_preference)
 			break;
-		rp = &r->r_next;
+		last = r;
 	}
-
-	new_r->r_next = r;
 	atomic_inc(&new_r->r_clntref);
-	write_lock_bh(&dn_fib_rules_lock);
-	*rp = new_r;
-	write_unlock_bh(&dn_fib_rules_lock);
+
+	if (last)
+		hlist_add_after_rcu(&last->r_hlist, &new_r->r_hlist);
+	else
+		hlist_add_before_rcu(&new_r->r_hlist, &r->r_hlist);
 	return 0;
 }
 
@@ -210,10 +217,12 @@ int dn_fib_lookup(const struct flowi *flp, struct dn_fib_res *res)
 	struct dn_fib_table *tb;
 	__le16 saddr = flp->fld_src;
 	__le16 daddr = flp->fld_dst;
+	struct hlist_node *node;
 	int err;
 
-	read_lock(&dn_fib_rules_lock);
-	for(r = dn_fib_rules; r; r = r->r_next) {
+	rcu_read_lock();
+
+	hlist_for_each_entry_rcu(r, node, &dn_fib_rules, r_hlist) {
 		if (((saddr^r->r_src) & r->r_srcmask) ||
 		    ((daddr^r->r_dst) & r->r_dstmask) ||
 #ifdef CONFIG_DECNET_ROUTE_FWMARK
@@ -228,14 +237,14 @@ int dn_fib_lookup(const struct flowi *flp, struct dn_fib_res *res)
 				policy = r;
 				break;
 			case RTN_UNREACHABLE:
-				read_unlock(&dn_fib_rules_lock);
+				rcu_read_unlock();
 				return -ENETUNREACH;
 			default:
 			case RTN_BLACKHOLE:
-				read_unlock(&dn_fib_rules_lock);
+				rcu_read_unlock();
 				return -EINVAL;
 			case RTN_PROHIBIT:
-				read_unlock(&dn_fib_rules_lock);
+				rcu_read_unlock();
 				return -EACCES;
 		}
 
@@ -246,16 +255,16 @@ int dn_fib_lookup(const struct flowi *flp, struct dn_fib_res *res)
 			res->r = policy;
 			if (policy)
 				atomic_inc(&policy->r_clntref);
-			read_unlock(&dn_fib_rules_lock);
+			rcu_read_unlock();
 			return 0;
 		}
 		if (err < 0 && err != -EAGAIN) {
-			read_unlock(&dn_fib_rules_lock);
+			rcu_read_unlock();
 			return err;
 		}
 	}
 
-	read_unlock(&dn_fib_rules_lock);
+	rcu_read_unlock();
 	return -ESRCH;
 }
 
@@ -297,27 +306,23 @@ __le16 dn_fib_rules_policy(__le16 saddr, struct dn_fib_res *res, unsigned *flags
 
 static void dn_fib_rules_detach(struct net_device *dev)
 {
+	struct hlist_node *node;
 	struct dn_fib_rule *r;
 
-	for(r = dn_fib_rules; r; r = r->r_next) {
-		if (r->r_ifindex == dev->ifindex) {
-			write_lock_bh(&dn_fib_rules_lock);
+	hlist_for_each_entry(r, node, &dn_fib_rules, r_hlist) {
+		if (r->r_ifindex == dev->ifindex)
 			r->r_ifindex = -1;
-			write_unlock_bh(&dn_fib_rules_lock);
-		}
 	}
 }
 
 static void dn_fib_rules_attach(struct net_device *dev)
 {
+	struct hlist_node *node;
 	struct dn_fib_rule *r;
 
-	for(r = dn_fib_rules; r; r = r->r_next) {
-		if (r->r_ifindex == -1 && strcmp(dev->name, r->r_ifname) == 0) {
-			write_lock_bh(&dn_fib_rules_lock);
+	hlist_for_each_entry(r, node, &dn_fib_rules, r_hlist) {
+		if (r->r_ifindex == -1 && strcmp(dev->name, r->r_ifname) == 0)
 			r->r_ifindex = dev->ifindex;
-			write_unlock_bh(&dn_fib_rules_lock);
-		}
 	}
 }
 
@@ -387,18 +392,20 @@ static int dn_fib_fill_rule(struct sk_buff *skb, struct dn_fib_rule *r,
 
 int dn_fib_dump_rules(struct sk_buff *skb, struct netlink_callback *cb)
 {
-	int idx;
+	int idx = 0;
 	int s_idx = cb->args[0];
 	struct dn_fib_rule *r;
+	struct hlist_node *node;
 
-	read_lock(&dn_fib_rules_lock);
-	for(r = dn_fib_rules, idx = 0; r; r = r->r_next, idx++) {
+	rcu_read_lock();
+	hlist_for_each_entry(r, node, &dn_fib_rules, r_hlist) {
 		if (idx < s_idx)
 			continue;
 		if (dn_fib_fill_rule(skb, r, cb, NLM_F_MULTI) < 0)
 			break;
+		idx++;
 	}
-	read_unlock(&dn_fib_rules_lock);
+	rcu_read_unlock();
 	cb->args[0] = idx;
 
 	return skb->len;
@@ -406,6 +413,8 @@ int dn_fib_dump_rules(struct sk_buff *skb, struct netlink_callback *cb)
 
 void __init dn_fib_rules_init(void)
 {
+	INIT_HLIST_HEAD(&dn_fib_rules);
+	hlist_add_head(&default_rule.r_hlist, &dn_fib_rules);
 	register_netdevice_notifier(&dn_fib_rules_notifier);
 }