Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753213AbaFMKGn (ORCPT ); Fri, 13 Jun 2014 06:06:43 -0400 Received: from mx0.aculab.com ([213.249.233.131]:41640 "HELO mx0.aculab.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1753151AbaFMKGk (ORCPT ); Fri, 13 Jun 2014 06:06:40 -0400 From: David Laight To: "'Geert Uytterhoeven'" CC: Tom Herbert , "David S. Miller" , Linux-Next , Linux-sh list , "linux-kernel@vger.kernel.org" , "netdev@vger.kernel.org" Subject: RE: [-next] Regression: ssh log in slowdown Thread-Topic: [-next] Regression: ssh log in slowdown Thread-Index: AQHPhuOEjg6tqmc0skKORvvtsE7uQJtuurFwgAABkQCAABGuYA== Date: Fri, 13 Jun 2014 10:05:42 +0000 Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1725C2C3@AcuExch.aculab.com> References: <063D6719AE5E284EB5DD2968C1650D6D1725C134@AcuExch.aculab.com> In-Reply-To: Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.202.99.200] Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from base64 to 8bit by mail.home.local id s5DA6oQZ013295 From: Geert Uytterhoeven > Hi David, > > On Fri, Jun 13, 2014 at 10:49 AM, David Laight wrote: > > From: Of Geert Uytterhoeven > > ... > >> Note that I'm also using NFS root, which doesn't seem to be affected. > >> I can happily run "ls -R /" on the serial console during the 10 s delay in ssh. > > > > Are you sure that the delay during ssh login isn't just > > a reverse DNS timeout? > > Indeed, the ssh server sends a reverse DNS request twice, with 5s in between: ... > Interestingly, I don't see the forward DNS request after that, which > does happen in the good case. The forwards request is probably just copying some strange code from 'rshd' that tried to verify the reverse lookup by doing a forwards lookup on the result. That in itself used to cause us grief. The RDNS would (correctly) generate host.bar.baz.co.uk, since the 'domain' in etc/resolv.conf was bar.baz.co.uk the forwards lookup first tried host.bar.baz.co.uk.bar.baz.co.uk then host.bar.baz.co.uk.baz.co.uk one of which always timed out :-( (When the 'search' command was added we could avoid the request that timed out.) David ????{.n?+???????+%?????ݶ??w??{.n?+????{??G?????{ay?ʇڙ?,j??f???h?????????z_??(?階?ݢj"???m??????G????????????&???~???iO???z??v?^?m???? ????????I?