Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932517AbZKSD55 (ORCPT ); Wed, 18 Nov 2009 22:57:57 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932424AbZKSD55 (ORCPT ); Wed, 18 Nov 2009 22:57:57 -0500 Received: from mx1.redhat.com ([209.132.183.28]:46297 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932405AbZKSD54 (ORCPT ); Wed, 18 Nov 2009 22:57:56 -0500 Message-ID: <4B04C2AF.4040509@redhat.com> Date: Wed, 18 Nov 2009 22:59:43 -0500 From: Masami Hiramatsu User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.4pre) Gecko/20090922 Fedora/3.0-2.7.b4.fc11 Thunderbird/3.0b4 MIME-Version: 1.0 To: Mathieu Desnoyers CC: Jason Baron , linux-kernel@vger.kernel.org, mingo@elte.hu, hpa@zytor.com, tglx@linutronix.de, rostedt@goodmis.org, andi@firstfloor.org, roland@redhat.com, rth@redhat.com, "Paul E. McKenney" Subject: Re: [PATCH] notifier atomic call chain notrace References: <14acd28665b633909f7e9873861075fd657e9a52.1258580048.git.jbaron@redhat.com> <20091118233815.GA28962@Krystal> In-Reply-To: <20091118233815.GA28962@Krystal> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2677 Lines: 79 Mathieu Desnoyers wrote: > * Jason Baron (jbaron@redhat.com) wrote: >> Note that this is conditional on gcc >= 4.5. Also there is a !lockdep >> condition. This is b/c the die_notifier takes an rcu_read_lock() on the >> int3 trap, which then causes another one etc. Since, we aren't going to be >> installing removing the handler, the rcu_read_lock() could be avoided for this >> case with some code restructuring. >> > [snip] > > Would the following patch help ? I use it in the LTTng tree to alleviate > this problem. Reviewed-by: Masami Hiramatsu The code itself seems OK for me. :-) I'd just like to hear the opinion from Ingo, since this change will change all atomic-notifier's locks to notrace. > notifier atomic call chain notrace > > In LTTng, being able to use the atomic notifier from cpu idle entry to > ensure the tracer flush the last events in the current subbuffer > requires the rcu read-side to be marked "notrace", otherwise it can end > up calling back into lockdep and the tracer. > > Also apply to the the die notifier. > > Signed-off-by: Mathieu Desnoyers > CC: "Paul E. McKenney" > CC: Jason Baron > CC: mingo@elte.hu > --- > kernel/notifier.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > Index: linux-2.6-lttng/kernel/notifier.c > =================================================================== > --- linux-2.6-lttng.orig/kernel/notifier.c 2009-11-12 17:58:56.000000000 -0500 > +++ linux-2.6-lttng/kernel/notifier.c 2009-11-12 18:03:28.000000000 -0500 > @@ -148,7 +148,7 @@ int atomic_notifier_chain_unregister(str > spin_lock_irqsave(&nh->lock, flags); > ret = notifier_chain_unregister(&nh->head, n); > spin_unlock_irqrestore(&nh->lock, flags); > - synchronize_rcu(); > + synchronize_sched(); > return ret; > } > EXPORT_SYMBOL_GPL(atomic_notifier_chain_unregister); > @@ -178,9 +178,9 @@ int __kprobes __atomic_notifier_call_cha > { > int ret; > > - rcu_read_lock(); > + rcu_read_lock_sched_notrace(); > ret = notifier_call_chain(&nh->head, val, v, nr_to_call, nr_calls); > - rcu_read_unlock(); > + rcu_read_unlock_sched_notrace(); > return ret; > } > EXPORT_SYMBOL_GPL(__atomic_notifier_call_chain); > -- Masami Hiramatsu Software Engineer Hitachi Computer Products (America), Inc. Software Solutions Division e-mail: mhiramat@redhat.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/