From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755650AbZCTUtG (ORCPT ); Fri, 20 Mar 2009 16:49:06 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753150AbZCTUsy (ORCPT ); Fri, 20 Mar 2009 16:48:54 -0400 Received: from mail-ew0-f165.google.com ([209.85.219.165]:33433 "EHLO mail-ew0-f165.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752640AbZCTUsx (ORCPT ); Fri, 20 Mar 2009 16:48:53 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=RXHwIQJmzL0Lkos2M5b6pvYcQY0Qfwi5QMMY8Koh2KtHNp1JDVSI1/HcabB7cCP+dZ 30x9xtN7g3CFXOxzYSzdwZoNdrvBlo+sXzAh09fSXmPlhVH3Ob1UWR+d469W1LQSMbFp OKPzShbRh18JKDAEPW5EVUbts7x+ModlCDdHw= Date: Fri, 20 Mar 2009 21:48:48 +0100 From: Frederic Weisbecker To: Ingo Molnar Cc: "Paul E. McKenney" , Steven Rostedt , LKML , Thomas Gleixner , Peter Zijlstra Subject: Re: [PATCH 0/5] [GIT PULL] updates for tip/tracing/ftrace Message-ID: <20090320204848.GA6044@nowhere> References: <20090318073903.GA31341@elte.hu> <20090319073357.GA14615@elte.hu> <20090320174331.GH6698@linux.vnet.ibm.com> <20090320183642.GA2070@elte.hu> <20090320183849.GA3657@elte.hu> <20090320191926.GJ6698@linux.vnet.ibm.com> <20090320192721.GI6224@elte.hu> <20090320194617.GA5934@nowhere> <20090320195414.GA24129@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090320195414.GA24129@elte.hu> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 20, 2009 at 08:54:14PM +0100, Ingo Molnar wrote: > > * Frederic Weisbecker wrote: > > > On Fri, Mar 20, 2009 at 08:27:21PM +0100, Ingo Molnar wrote: > > > > > > * Paul E. McKenney wrote: > > > > > > > On Fri, Mar 20, 2009 at 07:38:49PM +0100, Ingo Molnar wrote: > > > > > > > > > > * Ingo Molnar wrote: > > > > > > > > > > > > > This looks like it is RCU/stop_machine related. The CPU is > > > > > > > > stuck in in stop_machine? I see that rcu_torture is running. > > > > > > > > Does this go away if you turn off rcu_torture? > > > > > > > > > > > > > > Grasping at straws... Does Lai's rcu_barrier() fix help? > > > > > > > > > > > > which one is that? > > > > > > > > > > ok, found it. Will know in about ~24 hours whether it helps. > > > > > > > > http://lkml.org/lkml/2009/3/20/71 was the one I was thinking of, > > > > just to double-check. > > > > > > Yeah - i just picked it up into tip:core/rcu. > > > > > > I didnt immediately connect the two things, as 'tracer self-test' > > > does not lend itself to 'CPU hotplug and RCU race fix' - but indeed > > > in the case of the function tracer there's a dependency due to > > > stop_machine_run(). Thanks for point it out! > > > > > > Ingo > > > > > > I've successfully triggered a crash, the problem is that I can't be sure this is > > the same because I don't have a serial line on my x86-64, and the trace goes too far. > > Moreover boot_delay=N make it disappear. > > > > I can trigger it each time I boot with ftrace=function_graph and > > the following patch applied: > > > > diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c > > index 7c4142a..e9914a8 100644 > > --- a/kernel/rcutorture.c > > +++ b/kernel/rcutorture.c > > @@ -616,7 +616,7 @@ rcu_torture_writer(void *arg) > > static DEFINE_RCU_RANDOM(rand); > > > > VERBOSE_PRINTK_STRING("rcu_torture_writer task started"); > > - set_user_nice(current, 19); > > + set_user_nice(current, -1); > > > > do { > > schedule_timeout_uninterruptible(1); > > @@ -736,7 +736,7 @@ rcu_torture_reader(void *arg) > > struct timer_list t; > > > > VERBOSE_PRINTK_STRING("rcu_torture_reader task started"); > > - set_user_nice(current, 19); > > + set_user_nice(current, -1); > > if (irqreader && cur_ops->irqcapable) > > setup_timer_on_stack(&t, rcu_torture_timer, 0); > > i dont have a reproducer right now. Can you trigger it with latest > -tip, which has this commit included: > > 04cb9ac: rcu: rcu_barrier VS cpu_hotplug: Ensure callbacks in dead cpu are migrated to o > > ? > > Ingo I tested three times the same things but with 04cb9ac and... it didn't triggered anymore :-)