raw: convert raw sockets to RCU

Using rwlock in networking code is extremely risky.
writers can starve if enough readers are constantly
grabing the rwlock.

I thought rwlock were at fault and sent this patch:

https://lkml.org/lkml/2022/6/17/272

But Peter and Linus essentially told me rwlock had to be unfair.

We need to get rid of rwlock in networking code.

Without this fix, following script triggers soft lockups:

for i in {1..48}
do
 ping -f -n -q 127.0.0.1 &
 sleep 0.1
done

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 13 insertions, 15 deletions

diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c
index c0f2e3475984..f6119998700e 100644
--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c
@@ -61,9 +61,7 @@
 
 #define	ICMPV6_HDRLEN	4	/* ICMPv6 header, RFC 4443 Section 2.1 */
 
-struct raw_hashinfo raw_v6_hashinfo = {
-	.lock = __RW_LOCK_UNLOCKED(raw_v6_hashinfo.lock),
-};
+struct raw_hashinfo raw_v6_hashinfo;
 EXPORT_SYMBOL_GPL(raw_v6_hashinfo);
 
 bool raw_v6_match(struct net *net, struct sock *sk, unsigned short num,
@@ -143,9 +141,10 @@ EXPORT_SYMBOL(rawv6_mh_filter_unregister);
 static bool ipv6_raw_deliver(struct sk_buff *skb, int nexthdr)
 {
 	struct net *net = dev_net(skb->dev);
+	struct hlist_nulls_head *hlist;
+	struct hlist_nulls_node *hnode;
 	const struct in6_addr *saddr;
 	const struct in6_addr *daddr;
-	struct hlist_head *head;
 	struct sock *sk;
 	bool delivered = false;
 	__u8 hash;
@@ -154,11 +153,9 @@ static bool ipv6_raw_deliver(struct sk_buff *skb, int nexthdr)
 	daddr = saddr + 1;
 
 	hash = nexthdr & (RAW_HTABLE_SIZE - 1);
-	head = &raw_v6_hashinfo.ht[hash];
-	if (hlist_empty(head))
-		return false;
-	read_lock(&raw_v6_hashinfo.lock);
-	sk_for_each(sk, head) {
+	hlist = &raw_v6_hashinfo.ht[hash];
+	rcu_read_lock();
+	hlist_nulls_for_each_entry(sk, hnode, hlist, sk_nulls_node) {
 		int filtered;
 
 		if (!raw_v6_match(net, sk, nexthdr, daddr, saddr,
@@ -203,7 +200,7 @@ static bool ipv6_raw_deliver(struct sk_buff *skb, int nexthdr)
 			}
 		}
 	}
-	read_unlock(&raw_v6_hashinfo.lock);
+	rcu_read_unlock();
 	return delivered;
 }
 
@@ -337,14 +334,15 @@ void raw6_icmp_error(struct sk_buff *skb, int nexthdr,
 {
 	const struct in6_addr *saddr, *daddr;
 	struct net *net = dev_net(skb->dev);
-	struct hlist_head *head;
+	struct hlist_nulls_head *hlist;
+	struct hlist_nulls_node *hnode;
 	struct sock *sk;
 	int hash;
 
 	hash = nexthdr & (RAW_HTABLE_SIZE - 1);
-	head = &raw_v6_hashinfo.ht[hash];
-	read_lock(&raw_v6_hashinfo.lock);
-	sk_for_each(sk, head) {
+	hlist = &raw_v6_hashinfo.ht[hash];
+	rcu_read_lock();
+	hlist_nulls_for_each_entry(sk, hnode, hlist, sk_nulls_node) {
 		/* Note: ipv6_hdr(skb) != skb->data */
 		const struct ipv6hdr *ip6h = (const struct ipv6hdr *)skb->data;
 		saddr = &ip6h->saddr;
@@ -355,7 +353,7 @@ void raw6_icmp_error(struct sk_buff *skb, int nexthdr,
 			continue;
 		rawv6_err(sk, skb, NULL, type, code, inner_offset, info);
 	}
-	read_unlock(&raw_v6_hashinfo.lock);
+	rcu_read_unlock();
 }
 
 static inline int rawv6_rcv_skb(struct sock *sk, struct sk_buff *skb)