[PATCH bpf v7 07/13] bpf: sockmap, wake up polling after data copy

[John Fastabend <john.fastabend@gmail.com>]

When TCP stack has data ready to read sk_data_ready() is called. Sockmap
overwrites this with its own handler to call into BPF verdict program.
But, the original TCP socket had sock_def_readable that would additionally
wake up any user space waiters with sk_wake_async().

Sockmap saved the callback when the socket was created so call the saved
data ready callback and then we can wake up any epoll() logic waiting
on the read.

Note we call on 'copied >= 0' to account for returning 0 when a FIN is
received because we need to wake up user for this as well so they
can do the recvmsg() -> 0 and detect the shutdown.

Fixes: 04919bed948dc ("tcp: Introduce tcp_read_skb()")
Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
---
 net/core/skmsg.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/net/core/skmsg.c b/net/core/skmsg.c
index bc5ca973400c..3c0663f5cc3e 100644
--- a/net/core/skmsg.c
+++ b/net/core/skmsg.c
@@ -1198,12 +1198,21 @@ static int sk_psock_verdict_recv(struct sock *sk, struct sk_buff *skb)
 static void sk_psock_verdict_data_ready(struct sock *sk)
 {
 	struct socket *sock = sk->sk_socket;
+	int copied;
 
 	trace_sk_data_ready(sk);
 
 	if (unlikely(!sock || !sock->ops || !sock->ops->read_skb))
 		return;
-	sock->ops->read_skb(sk, sk_psock_verdict_recv);
+	copied = sock->ops->read_skb(sk, sk_psock_verdict_recv);
+	if (copied >= 0) {
+		struct sk_psock *psock;
+
+		rcu_read_lock();
+		psock = sk_psock(sk);
+		psock->saved_data_ready(sk);
+		rcu_read_unlock();
+	}
 }
 
 void sk_psock_start_verdict(struct sock *sk, struct sk_psock *psock)
-- 
2.33.0