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, 9 deletions

diff --git a/net/ipv4/raw_diag.c b/net/ipv4/raw_diag.c
index b6d92dc7b051..5f208e840d85 100644
--- a/net/ipv4/raw_diag.c
+++ b/net/ipv4/raw_diag.c
@@ -57,31 +57,32 @@ static bool raw_lookup(struct net *net, struct sock *sk,
 static struct sock *raw_sock_get(struct net *net, const struct inet_diag_req_v2 *r)
 {
 	struct raw_hashinfo *hashinfo = raw_get_hashinfo(r);
+	struct hlist_nulls_head *hlist;
+	struct hlist_nulls_node *hnode;
 	struct sock *sk;
 	int slot;
 
 	if (IS_ERR(hashinfo))
 		return ERR_CAST(hashinfo);
 
-	read_lock(&hashinfo->lock);
+	rcu_read_lock();
 	for (slot = 0; slot < RAW_HTABLE_SIZE; slot++) {
-		sk_for_each(sk, &hashinfo->ht[slot]) {
+		hlist = &hashinfo->ht[slot];
+		hlist_nulls_for_each_entry(sk, hnode, hlist, sk_nulls_node) {
 			if (raw_lookup(net, sk, r)) {
 				/*
 				 * Grab it and keep until we fill
-				 * diag meaage to be reported, so
+				 * diag message to be reported, so
 				 * caller should call sock_put then.
-				 * We can do that because we're keeping
-				 * hashinfo->lock here.
 				 */
-				sock_hold(sk);
-				goto out_unlock;
+				if (refcount_inc_not_zero(&sk->sk_refcnt))
+					goto out_unlock;
 			}
 		}
 	}
 	sk = ERR_PTR(-ENOENT);
 out_unlock:
-	read_unlock(&hashinfo->lock);
+	rcu_read_unlock();
 
 	return sk;
 }
@@ -141,6 +142,8 @@ static void raw_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
 	struct raw_hashinfo *hashinfo = raw_get_hashinfo(r);
 	struct net *net = sock_net(skb->sk);
 	struct inet_diag_dump_data *cb_data;
+	struct hlist_nulls_head *hlist;
+	struct hlist_nulls_node *hnode;
 	int num, s_num, slot, s_slot;
 	struct sock *sk = NULL;
 	struct nlattr *bc;
@@ -157,7 +160,8 @@ static void raw_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
 	for (slot = s_slot; slot < RAW_HTABLE_SIZE; s_num = 0, slot++) {
 		num = 0;
 
-		sk_for_each(sk, &hashinfo->ht[slot]) {
+		hlist = &hashinfo->ht[slot];
+		hlist_nulls_for_each_entry(sk, hnode, hlist, sk_nulls_node) {
 			struct inet_sock *inet = inet_sk(sk);
 
 			if (!net_eq(sock_net(sk), net))