From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755538AbZHYSCf (ORCPT ); Tue, 25 Aug 2009 14:02:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755250AbZHYSCf (ORCPT ); Tue, 25 Aug 2009 14:02:35 -0400 Received: from tomts20.bellnexxia.net ([209.226.175.74]:33624 "EHLO tomts20-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755154AbZHYSCe (ORCPT ); Tue, 25 Aug 2009 14:02:34 -0400 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AigFADPEk0pMROOX/2dsb2JhbACBU9dShBoF Date: Tue, 25 Aug 2009 14:02:33 -0400 From: Mathieu Desnoyers To: "Paul E. McKenney" Cc: Ingo Molnar , Lai Jiangshan , linux-kernel@vger.kernel.org, dipankar@in.ibm.com, akpm@linux-foundation.org, josht@linux.vnet.ibm.com, dvhltc@us.ibm.com, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Paul Mundt Subject: Re: [PATCH -tip 0/2] Temporary RCU fixes for notrace and hotplug CPU Message-ID: <20090825180233.GA2448@Krystal> References: <20090824164112.GA13693@linux.vnet.ibm.com> <20090825065501.GA29162@elte.hu> <20090825080047.GA16139@elte.hu> <20090825161208.GE6616@linux.vnet.ibm.com> <20090825162549.GB25058@Krystal> <20090825171136.GG6616@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: <20090825171136.GG6616@linux.vnet.ibm.com> X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.6.27.31-grsec (i686) X-Uptime: 13:57:02 up 7 days, 4:46, 2 users, load average: 0.70, 0.41, 0.26 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 * Paul E. McKenney (paulmck@linux.vnet.ibm.com) wrote: > On Tue, Aug 25, 2009 at 12:25:49PM -0400, Mathieu Desnoyers wrote: > > * Paul E. McKenney (paulmck@linux.vnet.ibm.com) wrote: > > > On Tue, Aug 25, 2009 at 10:00:47AM +0200, Ingo Molnar wrote: > > > > > > > > btw., i'm still seeing crashes with the latest RCU bits: > > > > > > > > [ 20.621740] Testing event sys_enter_futex: OK > > > > [ 20.629738] Testing event sys_exit_futex: OK > > > > [ 20.637737] Testing event lock_acquire: [reboot] > > > > > > > > Possibly due to infinite recursion as well. Config attached. > > > > > > Color me confused... > > > > > > Unless someone has a better idea, I will send in a patch that adds > > > "notrace" to every RCU API member used by any file in the kernel > > > that has "trace" in its name (excluding ptrace.c and rcutree_trace.c, > > > of course). This list is as follows: > > > > > > call_rcu() > > > call_rcu_sched() > > > rcu_read_lock() > > > rcu_read_unlock() > > > > > > So, any better ideas? > > > > Tracers using RCU should use the _notrace() version of read_lock/unlock. > > I think the callers should be fixed rather than RCU. > > > > Tracepoints have been designed to use the _notrace variant on the > > instrumentation site. The core of tracepoint management use > > call_rcu_sched(), which can be traced without any problem. > > > > I have not followed the late tracing development as closely though, so > > errors might have crept in. > > Or I might have inadvertently broken something in a non-obvious (to me, > anyway) manner. > > So, would you be willing to look at commit bc33f24bd in the -tip > tree and see if there is anything I broke other than the now-fixed > rcu_read_lock_sched_notrace() and rcu_read_unlock_sched_notrace()? > And for that matter, whether my alleged fix for these two API members > really does fix the problem (-tip commit 7c614d6461)? > > The -tip tree is at: > > git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git > > And these patches are on the tip/core/rcu branch. > sure, here we go: static inline void rcu_read_lock_sched_notrace(void) { preempt_disable_notrace(); + __acquire(RCU_SCHED); + rcu_read_acquire(); } and static inline void rcu_read_unlock_sched_notrace(void) { + rcu_read_release(); + __release(RCU_SCHED); preempt_enable_notrace(); } will make those _notrace primitives call into lockdep. I don't think this is correct, and this might be causing your problem. rcu_read_acquire/release are calling lock_acquire/release, those should be removed. __acquire() simply seems to be defined to a gcc "context" attribute, probably for the sparse checker. I think it should be safe to leave them there. Mathieu > Thanx, Paul -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68