[PATCH net-next] mptcp: silence warning in subflow_data_ready()

[Davide Caratti]

since commit d47a72152097 ("mptcp: fix race in subflow_data_ready()"), it
is possible to observe a regression in MP_JOIN kselftests. For sockets in
TCP_CLOSE state, it's not sufficient to just wake up the main socket: we
also need to ensure that received data are made available to the reader.
Silence the WARN_ON_ONCE() in these cases: it preserves the syzkaller fix
and restores kselftests when they are ran as follows:

  # while true; do
  > make KBUILD_OUTPUT=/tmp/kselftest TARGETS=net/mptcp kselftest
  > done

Reported-by: Florian Westphal <f...@strlen.de>
Fixes: d47a72152097 ("mptcp: fix race in subflow_data_ready()")
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/47
Signed-off-by: Davide Caratti <dcara...@redhat.com>
---
 net/mptcp/subflow.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 9f7f3772c13c..519122e66f17 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -869,18 +869,19 @@ void mptcp_space(const struct sock *ssk, int *space, int 
*full_space)
 static void subflow_data_ready(struct sock *sk)
 {
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+       u16 state = 1 << inet_sk_state_load(sk);
        struct sock *parent = subflow->conn;
        struct mptcp_sock *msk;
 
        msk = mptcp_sk(parent);
-       if ((1 << inet_sk_state_load(sk)) & (TCPF_LISTEN | TCPF_CLOSE)) {
+       if (state & TCPF_LISTEN) {
                set_bit(MPTCP_DATA_READY, &msk->flags);
                parent->sk_data_ready(parent);
                return;
        }
 
        WARN_ON_ONCE(!__mptcp_check_fallback(msk) && !subflow->mp_capable &&
-                    !subflow->mp_join);
+                    !subflow->mp_join && !(state & TCPF_CLOSE));
 
        if (mptcp_subflow_data_available(sk))
                mptcp_data_ready(parent, sk);
-- 
2.26.2