Recently, some fallback have been initiated, while the connection was
not supposed to fallback.

Add a safety check with a warning to detect when an wrong attempt to
fallback is being done. This should help detecting any future issues
quicker.

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
Notes:
 - I guess this patch could be sent to -net as well.
 - We could also squash this in one of the previous commit, but because
   the two are needed to avoid the warning, maybe better with a
   dedicated commit?
---
 net/mptcp/protocol.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index bac5c925a72f6637e33ada9869984c5902bd6a43..3d72ca1553227cb41ba8c205f42d1f01cc264a7e 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -1198,6 +1198,8 @@ static inline void __mptcp_do_fallback(struct mptcp_sock *msk)
 		pr_debug("TCP fallback already done (msk=%p)\n", msk);
 		return;
 	}
+	if (WARN_ON_ONCE(!READ_ONCE(msk->allow_infinite_fallback)))
+		return;
 	set_bit(MPTCP_FALLBACK_DONE, &msk->flags);
 }
 

-- 
2.47.1