mptcp: drop legacy code

After the previous commits the PM worker can't race anymore
with the unaccepted subflow close and disposal, as the msk
keeps a reference to such subflow.

We can remove the now irrelevant and confusing checks explicitly
preventing the mentioned race.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Matthieu Baerts <matthieu.baerts@tessares.net>

net/mptcp/options.c

@@ -988,12 +988,7 @@ static bool check_fully_established(struct mptcp_sock *msk, struct sock *ssk,
  mptcp_subflow_fully_established(subflow, mp_opt);
 
 check_notify:
- /* if the subflow is not already linked into the conn_list, we can't
- * notify the PM: this subflow is still on the listener queue
- * and the PM possibly acquiring the subflow lock could race with
- * the listener close
- */
- if (likely(subflow->pm_notified) || list_empty(&subflow->node))
+ if (likely(subflow->pm_notified))
  return true;
 
  subflow->pm_notified = 1;

net/mptcp/subflow.c

@@ -1937,11 +1937,10 @@ static void subflow_ulp_release(struct sock *ssk)
 
  sk = ctx->conn;
  if (sk) {
- /* if the msk has been orphaned, keep the ctx
- * alive, will be freed by __mptcp_close_ssk(),
- * when the subflow is still unaccepted
+ /* if the subflow has been closed by the TCP stack, keep
+ * the ctx alive, will be freed by __mptcp_close_ssk()
  */
- release = ctx->disposable || list_empty(&ctx->node);
+ release = ctx->disposable;
  sock_put(sk);
  }