From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758483AbZGHWUV (ORCPT ); Wed, 8 Jul 2009 18:20:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754766AbZGHWUH (ORCPT ); Wed, 8 Jul 2009 18:20:07 -0400 Received: from ru.mvista.com ([213.79.90.228]:48056 "EHLO buildserver.ru.mvista.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1754626AbZGHWUG (ORCPT ); Wed, 8 Jul 2009 18:20:06 -0400 Date: Thu, 9 Jul 2009 02:20:03 +0400 From: Anton Vorontsov To: Andrew Morton Cc: torvalds@linux-foundation.org, a.p.zijlstra@chello.nl, oleg@redhat.com, mingo@elte.hu, linux-kernel@vger.kernel.org, netdev@vger.kernel.org Subject: [PATCH] netpoll: Fix carrier detection for drivers that are using phylib Message-ID: <20090708222003.GA12318@oksana.dev.rtsoft.ru> Reply-To: avorontsov@ru.mvista.com References: <20090707235812.GA12824@oksana.dev.rtsoft.ru> <20090708005000.GA12380@redhat.com> <1247034263.9777.24.camel@twins> <20090708141024.f8b581c5.akpm@linux-foundation.org> <20090708213331.GA9346@oksana.dev.rtsoft.ru> <20090708144744.5555b88d.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20090708144744.5555b88d.akpm@linux-foundation.org> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Using early netconsole and gianfar driver this error pops up: netconsole: timeout waiting for carrier It appears that net/core/netpoll.c:netpoll_setup() is using cond_resched() in a loop waiting for a carrier. The thing is that cond_resched() is a no-op when system_state != SYSTEM_RUNNING, and so drivers/net/phy/phy.c's state_queue is never scheduled, therefore link detection doesn't work. I belive that the main problem is in cond_resched()[1], but despite how the cond_resched() story ends, it might be a good idea to call msleep(1) instead of cond_resched(), as suggested by Andrew Morton. [1] http://lkml.org/lkml/2009/7/7/463 Signed-off-by: Anton Vorontsov --- On Wed, Jul 08, 2009 at 02:47:44PM -0700, Andrew Morton wrote: > (belatedly cc'ing netdev) > > Original diagnosis: > > : Using early netconsole and gianfar driver this error pops up: > : > : netconsole: timeout waiting for carrier > : > : It appears that net/core/netpoll.c:netpoll_setup() is using > : cond_resched() in a loop waiting for a carrier. > : > : The thing is that cond_resched() is a no-op when system_state != > : SYSTEM_RUNNING, and so drivers/net/phy/phy.c's state_queue is never > : scheduled, therefore link detection doesn't work > > > On Thu, 9 Jul 2009 01:33:31 +0400 Anton Vorontsov wrote: > > On Wed, Jul 08, 2009 at 02:10:24PM -0700, Andrew Morton wrote: > > > > On Wed, 8 Jul 2009 09:12:30 -0700 (PDT) Linus Torvalds wrote: > > > > That said, I do agree that maybe SYSTEM_RUNNING isn't the right check. > > > > Testing that the scheduler is initialized may be the more correct one. I > > > > think the SYSTEM_RUNNING one just comes from that being used for other > > > > debug issues. > > > > > > Agreed. system_state is too general. > > > > > > If we specifically want to know whether it is safe to call schedule() then > > > let's create a global boolean it_is_safe_to_call_schedule and test that, > > > rather than testing something which indirectly and unreliably implies "it > > > is safe to call schedule". If that boolean already exists then no-brainer. > > > > > > All that being said, I wonder if the netconsole code should be using > > > msleep(1) instead. Spinning on cond_resched() is a bit rude. But one > > > would have to verify that it is safe to call schedule() at this time, and > > > for the netconsole caller, this is dubious. > > > > What do you mean by "verify that it is safe"? If it works, > > can I assume that it's safe? ;-) It works, fwiw. > > > > netconsole is supposed to be available as early as possible in boot for > obvious reasons. I'd say there's a decent risk now and in the future that > netconsole will be initialised prior to the scheduler being available. > > In fact, if "netconsole: timeout waiting for carrier" newly added to > netpoll_setup() a depedency on the scheduler being available then perhaps > that was an incorrect change. 'git blame' says that carrier detection code didn't change since 2.6.12 (where git history starts), PHYLIB is using workqueue since its submission (2.6.13). And SYSTEM_RUNNING check was added in 2.6.16. So it's not a new dependency. The netpoll code is using msleep() just a few lines below cond_resched(), so we won't make things worse. ;-) Thanks! net/core/netpoll.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/net/core/netpoll.c b/net/core/netpoll.c index 9675f31..df30feb 100644 --- a/net/core/netpoll.c +++ b/net/core/netpoll.c @@ -740,7 +740,7 @@ int netpoll_setup(struct netpoll *np) np->name); break; } - cond_resched(); + msleep(1); } /* If carrier appears to come up instantly, we don't -- 1.6.3.3