[bpf PATCH] net: tcp_bpf, correctly handle DONT_WAIT flags and timeo == 0

[John Fastabend]

The tcp_bpf_wait_data() routine needs to check timeo != 0 before
calling sk_wait_event() otherwise we may see unexpected stalls
on receiver.

Arika did all the leg work here I just formaatted, posted and ran
a few tests.

Fixes: 604326b41a6fb ("bpf, sockmap: convert to generic sk_msg interface")
Reported-by: Arika Chen <eagles...@gmail.com>
Suggested-by: Arika Chen <eagles...@gmail.com>
Signed-off-by: John Fastabend <john.fastab...@gmail.com>
---
 net/ipv4/tcp_bpf.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
index 1bb7321a256d..27206b2064db 100644
--- a/net/ipv4/tcp_bpf.c
+++ b/net/ipv4/tcp_bpf.c
@@ -27,7 +27,10 @@ static int tcp_bpf_wait_data(struct sock *sk, struct 
sk_psock *psock,
                             int flags, long timeo, int *err)
 {
        DEFINE_WAIT_FUNC(wait, woken_wake_function);
-       int ret;
+       int ret = 0;
+
+       if (!timeo)
+               return ret;
 
        add_wait_queue(sk_sleep(sk), &wait);
        sk_set_bit(SOCKWQ_ASYNC_WAITDATA, sk);