netdev - [PATCH net-next 1/3] neighbour: add RCU protection to neigh

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Message-ID: <20240418095106.3680616-2-edumazet@google.com>
Date: Thu, 18 Apr 2024 09:51:04 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, David Ahern <dsahern@...nel.org>, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next 1/3] neighbour: add RCU protection to neigh_tables[]

In order to remove RTNL protection from neightbl_dump_info()
and neigh_dump_info() later, we need to add
RCU protection to neigh_tables[].

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/core/neighbour.c | 30 +++++++++++++++++++-----------
 1 file changed, 19 insertions(+), 11 deletions(-)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 552719c3bbc3d7869c49028f4c5c9102d1ae9b0a..33913dbf4023bcb1f18107fc3b5c26280dce7341 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -1769,7 +1769,7 @@ static void neigh_parms_destroy(struct neigh_parms *parms)
 
 static struct lock_class_key neigh_table_proxy_queue_class;
 
-static struct neigh_table *neigh_tables[NEIGH_NR_TABLES] __read_mostly;
+static struct neigh_table __rcu *neigh_tables[NEIGH_NR_TABLES] __read_mostly;
 
 void neigh_table_init(int index, struct neigh_table *tbl)
 {
@@ -1826,13 +1826,19 @@ void neigh_table_init(int index, struct neigh_table *tbl)
 	tbl->last_flush = now;
 	tbl->last_rand	= now + tbl->parms.reachable_time * 20;
 
-	neigh_tables[index] = tbl;
+	rcu_assign_pointer(neigh_tables[index], tbl);
 }
 EXPORT_SYMBOL(neigh_table_init);
 
+/*
+ * Only called from ndisc_cleanup(), which means this is dead code
+ * because we no longer can unload IPv6 module.
+ */
 int neigh_table_clear(int index, struct neigh_table *tbl)
 {
-	neigh_tables[index] = NULL;
+	RCU_INIT_POINTER(neigh_tables[index], NULL);
+	synchronize_rcu();
+
 	/* It is not clean... Fix it to unload IPv6 module safely */
 	cancel_delayed_work_sync(&tbl->managed_work);
 	cancel_delayed_work_sync(&tbl->gc_work);
@@ -1864,10 +1870,10 @@ static struct neigh_table *neigh_find_table(int family)
 
 	switch (family) {
 	case AF_INET:
-		tbl = neigh_tables[NEIGH_ARP_TABLE];
+		tbl = rcu_dereference_rtnl(neigh_tables[NEIGH_ARP_TABLE]);
 		break;
 	case AF_INET6:
-		tbl = neigh_tables[NEIGH_ND_TABLE];
+		tbl = rcu_dereference_rtnl(neigh_tables[NEIGH_ND_TABLE]);
 		break;
 	}
 
@@ -2331,7 +2337,7 @@ static int neightbl_set(struct sk_buff *skb, struct nlmsghdr *nlh,
 	ndtmsg = nlmsg_data(nlh);
 
 	for (tidx = 0; tidx < NEIGH_NR_TABLES; tidx++) {
-		tbl = neigh_tables[tidx];
+		tbl = rcu_dereference_rtnl(neigh_tables[tidx]);
 		if (!tbl)
 			continue;
 		if (ndtmsg->ndtm_family && tbl->family != ndtmsg->ndtm_family)
@@ -2519,7 +2525,7 @@ static int neightbl_dump_info(struct sk_buff *skb, struct netlink_callback *cb)
 	for (tidx = 0; tidx < NEIGH_NR_TABLES; tidx++) {
 		struct neigh_parms *p;
 
-		tbl = neigh_tables[tidx];
+		tbl = rcu_dereference_rtnl(neigh_tables[tidx]);
 		if (!tbl)
 			continue;
 
@@ -2879,7 +2885,7 @@ static int neigh_dump_info(struct sk_buff *skb, struct netlink_callback *cb)
 	s_t = cb->args[0];
 
 	for (t = 0; t < NEIGH_NR_TABLES; t++) {
-		tbl = neigh_tables[t];
+		tbl = rcu_dereference_rtnl(neigh_tables[t]);
 
 		if (!tbl)
 			continue;
@@ -3143,14 +3149,15 @@ int neigh_xmit(int index, struct net_device *dev,
 	       const void *addr, struct sk_buff *skb)
 {
 	int err = -EAFNOSUPPORT;
+
 	if (likely(index < NEIGH_NR_TABLES)) {
 		struct neigh_table *tbl;
 		struct neighbour *neigh;
 
-		tbl = neigh_tables[index];
-		if (!tbl)
-			goto out;
 		rcu_read_lock();
+		tbl = rcu_dereference(neigh_tables[index]);
+		if (!tbl)
+			goto out_unlock;
 		if (index == NEIGH_ARP_TABLE) {
 			u32 key = *((u32 *)addr);
 
@@ -3166,6 +3173,7 @@ int neigh_xmit(int index, struct net_device *dev,
 			goto out_kfree_skb;
 		}
 		err = READ_ONCE(neigh->output)(neigh, skb);
+out_unlock:
 		rcu_read_unlock();
 	}
 	else if (index == NEIGH_LINK_TABLE) {
-- 
2.44.0.683.g7961c838ac-goog