From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755826AbZHYSgS (ORCPT ); Tue, 25 Aug 2009 14:36:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755797AbZHYSgR (ORCPT ); Tue, 25 Aug 2009 14:36:17 -0400 Received: from e7.ny.us.ibm.com ([32.97.182.137]:37496 "EHLO e7.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755782AbZHYSgR (ORCPT ); Tue, 25 Aug 2009 14:36:17 -0400 Date: Tue, 25 Aug 2009 11:36:13 -0700 From: "Paul E. McKenney" To: Mathieu Desnoyers 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: [PATCH -tip] Re: [PATCH -tip 0/2] Temporary RCU fixes for notrace and hotplug CPU Message-ID: <20090825183613.GJ6616@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090825180233.GA2448@Krystal> User-Agent: Mutt/1.5.15+20070412 (2007-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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(); }