From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932775AbZHZAxN (ORCPT ); Tue, 25 Aug 2009 20:53:13 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932744AbZHZAxM (ORCPT ); Tue, 25 Aug 2009 20:53:12 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:56394 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S932736AbZHZAxL (ORCPT ); Tue, 25 Aug 2009 20:53:11 -0400 Message-ID: <4A948780.6030005@cn.fujitsu.com> Date: Wed, 26 Aug 2009 08:53:20 +0800 From: Lai Jiangshan User-Agent: Thunderbird 2.0.0.6 (Windows/20070728) MIME-Version: 1.0 To: paulmck@linux.vnet.ibm.com CC: Mathieu Desnoyers , Ingo Molnar , 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] Re: [PATCH -tip 0/2] Temporary RCU fixes for notrace and hotplug CPU 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> <20090825180233.GA2448@Krystal> <20090825183613.GJ6616@linux.vnet.ibm.com> In-Reply-To: <20090825183613.GJ6616@linux.vnet.ibm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Paul E. McKenney wrote: > On Tue, Aug 25, 2009 at 02:02:33PM -0400, Mathieu Desnoyers wrote: >> * 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. > > Thank you for looking this over, Mathieu!!! Please see below for patch. > > Thanx, Paul > > ------------------------------------------------------------------------ > > Remove lockdep annotations from RCU's _notrace() API members. > > The lockdep annotations rcu_read_acquire() and rcu_read_release() > might lead to infinite looping if called from lockdep. So this patch > removes them. > > Suggested-by: Mathieu Desnoyers > Signed-off-by: Paul E. McKenney > > rcupdate.h | 2 -- > 1 file changed, 2 deletions(-) > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > index 8b4422c..95e0615 100644 > --- a/include/linux/rcupdate.h > +++ b/include/linux/rcupdate.h > @@ -195,7 +195,6 @@ static inline notrace void rcu_read_lock_sched_notrace(void) > { > preempt_disable_notrace(); > __acquire(RCU_SCHED); > - rcu_read_acquire(); > } > > /* > @@ -211,7 +210,6 @@ static inline void rcu_read_unlock_sched(void) > } > static inline notrace void rcu_read_unlock_sched_notrace(void) > { > - rcu_read_release(); > __release(RCU_SCHED); > preempt_enable_notrace(); > } > > I remembered I have suggested this ... Reviewed-by: Lai Jiangshan Lai Jiangshan wrote: > >> { >> preempt_disable_notrace(); >> + __acquire(RCU_SCHED); >> + rcu_read_acquire(); >> } >> > > It may cause infinity recursion. > rcu_read_acquire() calls rcu_read_lock_sched_notrace() > before current->lockdep_recursion is set to 1 when tracing in on, > thus infinity recursion occurs. > > Lai >