Re: [RFC PATCH] sctp: Don't lookup dst if transport dst is still valid

On 2013年07月02日 23:55, Neil Horman wrote:

On Tue, Jul 02, 2013 at 10:29:28AM -0400, Vlad Yasevich wrote:

quoted

On 07/02/2013 02:39 AM, Fan Du wrote:

quoted

When sctp sits on IPv6, sctp_transport_dst_check pass cookie as ZERO,
as a result ip6_dst_check always fail out. This behaviour makes
transport->dst useless, because every sctp_packet_transmit must look
for valid dst(Is this what supposed to be?)

One aggressive way is to call rt_genid_bump which invalid all dst to
make new dst for transport, apparently it also hurts others.
I'm sure this may not be the best for all, so any commnets?

Signed-off-by: Fan Du<redacted>
---
  include/net/sctp/sctp.h |   18 ++++++++++++------
  net/sctp/ipv6.c         |    2 ++
  2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h
index cd89510..f05af01 100644
--- a/include/net/sctp/sctp.h
+++ b/include/net/sctp/sctp.h

@@ -719,14 +719,20 @@ static inline void sctp_v4_map_v6(union sctp_addr *addr)
  	addr->v6.sin6_addr.s6_addr32[2] = htonl(0x0000ffff);
  }

-/* The cookie is always 0 since this is how it's used in the
- * pmtu code.
- */
+/* Set cookie with the right one for IPv6 and zero for others */
  static inline struct dst_entry *sctp_transport_dst_check(struct sctp_transport *t)
  {
-	if (t->dst&&  !dst_check(t->dst, 0)) {
-		dst_release(t->dst);
-		t->dst = NULL;
+
+	if (t->dst) {
+		struct rt6_info *rt = (struct rt6_info *)t->dst;
+		u32 cookie = 0;
+
+		if ((t->af_specific->sa_family == AF_INET6)&&  rt->rt6i_node)	
+			cookie = rt->rt6i_node->fn_sernum;	
+		if (!dst_check(t->dst, cookie)) {
+			dst_release(t->dst);
+			t->dst = NULL;
+		}
  	}

I think it would be better if we stored the dst_cookie in the
transport structure and initialized it at lookup time.   If you do
that, then if the route table changes, we'd correctly detect it
without artificially bumping rt_genid (and hurting ipv4).

Agreed, thats how we do it for ipv4, IIRC

                                  ^^^^
Hello Neil

I'm sorry I didn't find such things about IPv4.

sctp_transport_dst_check
  -> ipv4_dst_check
    -> rt_is_expired
            ^^^^^^^^^
By "expired", currently we *do* check rt->rt_genid against net->rt_genid,
and for IPv4, every adding/deleting an IPv4 address will bump net->rt_genid,
(this does impact IPv6 dst checking as well) so when I delete an IPv4 address,
ipv4_dst_check failed as expected to look for new dst, basically that's what
I find after checking the code for IPv4 cookie things as mentioned above.
Am I missing something here?

Neil

quoted

-vlad

quoted

  	return t->dst;

diff --git a/net/sctp/ipv6.c b/net/sctp/ipv6.c
index 8ee553b..cfae77e 100644
--- a/net/sctp/ipv6.c
+++ b/net/sctp/ipv6.c

@@ -137,6 +137,8 @@ static int sctp_inet6addr_event(struct notifier_block *this, unsigned long ev,
  		break;
  	}

+	/* invalid all transport dst forcing to look up new dst */
+	rt_genid_bump(net);
  	return NOTIFY_DONE;
  }

-- 
浮沉随浪只记今朝笑

--fan