[PATCH 5.10 024/102] mptcp: do not wakeup listener for MPJ subflows

From: Greg Kroah-Hartman
Date: Fri Mar 05 2021 - 07:29:31 EST


From: Paolo Abeni <pabeni@xxxxxxxxxx>

commit 52557dbc7538ecceb27ef2206719a47a8039a335 upstream.

MPJ subflows are not exposed as fds to user spaces. As such,
incoming MPJ subflows are removed from the accept queue by
tcp_check_req()/tcp_get_cookie_sock().

Later tcp_child_process() invokes subflow_data_ready() on the
parent socket regardless of the subflow kind, leading to poll
wakeups even if the later accept will block.

Address the issue by double-checking the queue state before
waking the user-space.

Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/164
Reported-by: Dr. David Alan Gilbert <dgilbert@xxxxxxxxxx>
Fixes: f296234c98a8 ("mptcp: Add handling of incoming MP_JOIN requests")
Reviewed-by: Mat Martineau <mathew.j.martineau@xxxxxxxxxxxxxxx>
Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/mptcp/subflow.c | 6 ++++++
1 file changed, 6 insertions(+)

--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -981,6 +981,12 @@ static void subflow_data_ready(struct so

msk = mptcp_sk(parent);
if (state & TCPF_LISTEN) {
+ /* MPJ subflow are removed from accept queue before reaching here,
+ * avoid stray wakeups
+ */
+ if (reqsk_queue_empty(&inet_csk(sk)->icsk_accept_queue))
+ return;
+
set_bit(MPTCP_DATA_READY, &msk->flags);
parent->sk_data_ready(parent);
return;