From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759438AbZEHLbz (ORCPT ); Fri, 8 May 2009 07:31:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752429AbZEHLbq (ORCPT ); Fri, 8 May 2009 07:31:46 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:35899 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751831AbZEHLbp (ORCPT ); Fri, 8 May 2009 07:31:45 -0400 Date: Fri, 8 May 2009 13:31:36 +0200 From: Ingo Molnar To: Steven Rostedt Cc: Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: [PATCH 4/4] ring-buffer: change WARN_ON from checking preempt_count to preemptible Message-ID: <20090508113136.GK11596@elte.hu> References: <20090508043250.372421144@goodmis.org> <20090508043331.726786617@goodmis.org> <20090507215427.4256cc3c.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Steven Rostedt wrote: > > > On Thu, 7 May 2009, Andrew Morton wrote: > > > On Fri, 08 May 2009 00:32:54 -0400 Steven Rostedt wrote: > > > > > From: Steven Rostedt > > > > > > There's a WARN_ON in the ring buffer code that makes sure preemption > > > is disabled. It checks "!preempt_count()". But when CONFIG_PREEMPT is not > > > enabled, preempt_count() is always zero, and this will trigger the warning. > > > > > > [ Impact: prevent false warning on non preemptible kernels ] > > > > > > Signed-off-by: Steven Rostedt > > > --- > > > kernel/trace/ring_buffer.c | 2 +- > > > 1 files changed, 1 insertions(+), 1 deletions(-) > > > > > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > > > index 3ae5ccf..3611706 100644 > > > --- a/kernel/trace/ring_buffer.c > > > +++ b/kernel/trace/ring_buffer.c > > > @@ -1688,7 +1688,7 @@ void ring_buffer_discard_commit(struct ring_buffer *buffer, > > > * committed yet. Thus we can assume that preemption > > > * is still disabled. > > > */ > > > - RB_WARN_ON(buffer, !preempt_count()); > > > + RB_WARN_ON(buffer, preemptible()); > > > > > > cpu = smp_processor_id(); > > > cpu_buffer = buffer->buffers[cpu]; > > > > smp_processor_id() will warn too. > > > > The difference is that RB_WARN_ON also disables the ring buffer. Yes, it's a more robust form of warning, in this context. Ingo