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

[Steffen Klassert <steffen.klassert@secunet.com>]

On Mon, Jan 14, 2013 at 12:26:59PM +0400, Yurij M. Plotnikov wrote:
> 
> Could you, please, tell me is there any news about this bug?
> 

Ok, I tried to reconstruct your testcase and I can confirm this bug.
It happens only on the first pmtu event on a given route. It works
if I run this test again. Actually it works sometimes even on the
first pmtu event, so it took me quite a while to understand what's ging on.

This is because standart routes (no pmtu or redirect events happened on
that route) are per cpu, so each cpu has it's own struct rtable. This means
that we do not invalidate the socket cached route if the NET_RX_SOFTIRQ
(which handles the pmtu event) is not served by the same cpu that the
sending socket uses. Exceptional routes (routes where a pmtu or redirect
event occured) are not per cpu, so there is no problem.

I'll send three patches in reply to this mail. Applying patch one and two
should fix the bug you reported. If you use IPsec you need patch three too.
The patches are marked as RFC, I'll do proper patch submission if you can
confirm that they fix this bug.