Re: [PATCH v1 net] net: Remove WARN_ON_ONCE(sk->sk_forward_alloc) from sk_stream_kill_queues().

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From:   Kuniyuki Iwashima <kuniyu@amazon.com>
Date:   Tue, 7 Feb 2023 16:37:13 -0800
> From:   Eric Dumazet <edumazet@google.com>
> Date:   Tue, 7 Feb 2023 20:25:19 +0100
> > On Tue, Feb 7, 2023 at 7:37 PM Kuniyuki Iwashima <kuniyu@amazon.com> wrote:
> > >
> > > In commit b5fc29233d28 ("inet6: Remove inet6_destroy_sock() in
> > > sk->sk_prot->destroy()."), we delay freeing some IPv6 resources
> > > from sk->destroy() to sk->sk_destruct().
> > >
> > > Christoph Paasch reported the commit started triggering
> > > WARN_ON_ONCE(sk->sk_forward_alloc) in sk_stream_kill_queues()
> > > (See [0 - 2]).
> > >
> > > For example, if inet6_sk(sk)->rxopt is not zero by setting
> > > IPV6_RECVPKTINFO or its friends, tcp_v6_do_rcv() clones a skb
> > > and calls skb_set_owner_r(), which charges it to sk.
> > 
> > skb_set_owner_r() in this place seems wrong.
> > This could lead to a negative sk->sk_forward_alloc
> > (because we have not sk_rmem_schedule() it ?)
> > 
> > Do you have a repro ?
> 
> I created a repro and confirmed sk->sk_forward_alloc was always positive.
> 
> ---8<---

Sorry, I missed unistd.h here while copy-and-paste.

#include <unistd.h>
> #include <stdio.h>
> 
> #include <sys/socket.h>
> #include <netinet/in.h>
> 
> #define IPV6_FLOWINFO		11
> 
> int main(void)
> {
> 	struct sockaddr_in6 addr = {
> 		.sin6_family = AF_INET6,
> 		.sin6_addr = in6addr_any,
> 		.sin6_port = htons(0),
> 	};
> 	int fd, ret = 0;
> 	socklen_t len;
> 
> 	ret = socket(AF_INET6, SOCK_STREAM, IPPROTO_IP);
> 	perror("socket");
> 	if (ret < 0)
> 		return ret;
> 
> 	fd = ret;
> 	ret = setsockopt(fd, SOL_IPV6, IPV6_FLOWINFO, &(int){1}, sizeof(int));
> 	perror("setsockopt");
> 
> 	ret = bind(fd, (struct sockaddr *)&addr, sizeof(addr));
> 	perror("bind");
> 	if (ret)
> 		goto out;
> 
> 	len = sizeof(addr);
> 	ret = getsockname(fd, (struct sockaddr *)&addr, &len);
> 	perror("getsockname");
> 	if (ret)
> 		goto out;
> 
> 	ret = connect(fd, (struct sockaddr *)&addr, len);
> 	perror("connect");
> 	if (ret)
> 		goto out;
> 
> out:
> 	close(fd);
> 
> 	return ret;
> }
> ---8<---