Re: PMTU discovery is broken on kernel 3.7.1 for UDP sockets

On 12/21/12 14:22, Steffen Klassert wrote:

On Thu, Dec 20, 2012 at 01:35:35PM +0100, Steffen Klassert wrote:
   

quoted

On Thu, Dec 20, 2012 at 03:22:13PM +0400, Yurij M. Plotnikov wrote:
     

quoted

On 12/20/12 11:34, Steffen Klassert wrote:
       

quoted

diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index 3c9d208..1049ce0 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c

@@ -1198,7 +1198,7 @@ static int do_ip_getsockopt(struct sock *sk, int level, int optname,
  	{
  		struct dst_entry *dst;
  		val = 0;
-		dst = sk_dst_get(sk);
+		dst = sk_dst_check(sk, 0);
  		if (dst) {
  			val = dst_mtu(dst);
  			dst_release(dst);
         

With this patch kernel 3.7.1 works perfect. All described problems
are fixed.
       

Thanks for testing!

I'm not sure if we can't use this as a fix. I think with this patch it
could happen that we return -ENOTCONN instead of a pmtu value on a
connected socket. Perhaps it is better to update the cached dst_entry in
ipv4_sk_update_pmtu() when we receive the -EMSGSIZE. I'll do some
investigation.

     

It turned out that updating the cached dst_entry in ipv4_sk_update_pmtu()
is not trivial. We need to implement proper socket locking and we need
socket release calback functions for all protocols that use
ipv4_sk_update_pmtu(), similar to tcp.

Today is my last office day for this year, so we probably have to defer
a solution to the next year.

Thanks.
   

Hi Steffen,

Could you, please, tell me is there any news about this bug?

Thanks in advance,
Yurij.