From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756613AbZLUP41 (ORCPT ); Mon, 21 Dec 2009 10:56:27 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756109AbZLUP40 (ORCPT ); Mon, 21 Dec 2009 10:56:26 -0500 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.124]:41946 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752059AbZLUP40 (ORCPT ); Mon, 21 Dec 2009 10:56:26 -0500 X-Authority-Analysis: v=1.0 c=1 a=3VcTWO7RLfwA:10 a=7U3hwN5JcxgA:10 a=mKBMVft-KihwrS45-8EA:9 a=yy3LbP1cpW1mNY2WAqgA:7 a=f1GVy3Iyhv7qSVgabQ_R8ZTdw6EA:4 X-Cloudmark-Score: 0 X-Originating-IP: 74.67.89.75 Subject: Re: [PATCH] tracing: Fix lockdep warning in global_clock() From: Steven Rostedt Reply-To: rostedt@goodmis.org To: Peter Zijlstra Cc: Li Zefan , Ingo Molnar , Frederic Weisbecker , LKML In-Reply-To: <1261406427.4314.155.camel@laptop> References: <4B2F1543.8020300@cn.fujitsu.com> <20091221064356.GA2378@elte.hu> <4B2F2588.8070501@cn.fujitsu.com> <1261406427.4314.155.camel@laptop> Content-Type: text/plain; charset="ISO-8859-15" Organization: Kihon Technologies Inc. Date: Mon, 21 Dec 2009 10:56:24 -0500 Message-ID: <1261410984.25193.8.camel@gandalf.stny.rr.com> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2009-12-21 at 15:40 +0100, Peter Zijlstra wrote: > On Mon, 2009-12-21 at 15:36 +0800, Li Zefan wrote: > > > +++ b/kernel/sched_clock.c > > @@ -250,9 +250,9 @@ unsigned long long cpu_clock(int cpu) > > unsigned long long clock; > > unsigned long flags; > > > > - raw_local_irq_save(flags); > > + local_irq_save(flags); > > clock = sched_clock_cpu(cpu); > > - raw_local_irq_restore(flags); > > + local_irq_restore(flags); > > > > return clock; > > } > > =============================================== > > > > I guess it's still true that lower level functions can take locks? > > No, I removed the locks from cpu_clock a while back. > The problem isn't with locks, it's with disabling interrupts. Lockdep keeps track of every time interrupts are disabled. If something disables interrupts with raw_* but then calls something that disables interrupts the normal way, lockdep will detect that interrupts are being disabled but they already are disabled. The internal irq disabled variable in lockdep wont match reality, and this will blow up (well, disable lockdep). So if cpu_clock disables interrupts with local_irq_* then so must trace_clock_global. -- Steve