[PATCH net] Revert "sctp: remove sctp_transport_pmtu_check"

[Xin Long]

This reverts commit 22d7be267eaa8114dcc28d66c1c347f667d7878a.

The dst's mtu in transport can be updated by a non sctp place like
in xfrm where the MTU information didn't get synced between asoc,
transport and dst, so it is still needed to do the pmtu check
in sctp_packet_config.
---
 include/net/sctp/sctp.h | 12 ++++++++++++
 net/sctp/output.c       |  3 +++
 2 files changed, 15 insertions(+)

diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h
index 8c2caa3..ab9242e 100644
--- a/include/net/sctp/sctp.h
+++ b/include/net/sctp/sctp.h
@@ -608,4 +608,16 @@ static inline __u32 sctp_dst_mtu(const struct dst_entry 
*dst)
                                 SCTP_DEFAULT_MINSEGMENT));
 }
 
+static inline bool sctp_transport_pmtu_check(struct sctp_transport *t)
+{
+       __u32 pmtu = sctp_dst_mtu(t->dst);
+
+       if (t->pathmtu == pmtu)
+               return true;
+
+       t->pathmtu = pmtu;
+
+       return false;
+}
+
 #endif /* __net_sctp_h__ */
diff --git a/net/sctp/output.c b/net/sctp/output.c
index 67939ad..0860122 100644
--- a/net/sctp/output.c
+++ b/net/sctp/output.c
@@ -118,6 +118,9 @@ void sctp_packet_config(struct sctp_packet *packet, __u32 
vtag,
                sctp_transport_route(tp, NULL, sp);
                if (asoc->param_flags & SPP_PMTUD_ENABLE)
                        sctp_assoc_sync_pmtu(asoc);
+       } else if (!sctp_transport_pmtu_check(tp)) {
+               if (asoc->param_flags & SPP_PMTUD_ENABLE)
+                       sctp_assoc_sync_pmtu(asoc);
        }
 
        if (asoc->pmtu_pending) {
-- 
2.1.0