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, 10 insertions, 1 deletions

diff --git a/include/net/raw.h b/include/net/raw.h
index 719d3556fc0a..d81eeeb8f1e6 100644
--- a/include/net/raw.h
+++ b/include/net/raw.h
@@ -33,9 +33,18 @@ int raw_rcv(struct sock *, struct sk_buff *);
 
 struct raw_hashinfo {
 	rwlock_t lock;
-	struct hlist_head ht[RAW_HTABLE_SIZE];
+	struct hlist_nulls_head ht[RAW_HTABLE_SIZE];
 };
 
+static inline void raw_hashinfo_init(struct raw_hashinfo *hashinfo)
+{
+	int i;
+
+	rwlock_init(&hashinfo->lock);
+	for (i = 0; i < RAW_HTABLE_SIZE; i++)
+		INIT_HLIST_NULLS_HEAD(&hashinfo->ht[i], i);
+}
+
 #ifdef CONFIG_PROC_FS
 int raw_proc_init(void);
 void raw_proc_exit(void);