Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761293AbYBSUdp (ORCPT ); Tue, 19 Feb 2008 15:33:45 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755292AbYBSUdb (ORCPT ); Tue, 19 Feb 2008 15:33:31 -0500 Received: from tomts5.bellnexxia.net ([209.226.175.25]:40710 "EHLO tomts5-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755303AbYBSUd3 (ORCPT ); Tue, 19 Feb 2008 15:33:29 -0500 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: Ah4FAMrLukdMQWRV/2dsb2JhbACBWa1z Date: Tue, 19 Feb 2008 15:33:26 -0500 From: Mathieu Desnoyers To: Jan Kiszka Cc: paulmck@linux.vnet.ibm.com, prasad@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, mingo@elte.hu, Gautham R Shenoy , linux-rt-users@vger.kernel.org, dipankar@in.ibm.com Subject: Re: Markers: multi-probe locking fun (was: Re: [PATCH 0/2] Markers Implementation for RCU Tracing - Ver II) Message-ID: <20080219203326.GA16701@Krystal> References: <20071231060911.GB6461@in.ibm.com> <20080103163055.GB27651@Krystal> <20080104105858.GA13865@in.ibm.com> <20080105124632.GA16576@Krystal> <20080107195038.GA5119@in.ibm.com> <47B97E63.3070205@siemens.com> <20080218194825.GF10471@linux.vnet.ibm.com> <47BB037C.6060306@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: <47BB037C.6060306@siemens.com> X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.6.21.3-grsec (i686) X-Uptime: 15:31:02 up 8 days, 16:31, 4 users, load average: 0.57, 0.43, 0.52 User-Agent: Mutt/1.5.16 (2007-06-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3101 Lines: 89 * Jan Kiszka (jan.kiszka@siemens.com) wrote: > Paul E. McKenney wrote: > > On Mon, Feb 18, 2008 at 01:47:31PM +0100, Jan Kiszka wrote: > >> K. Prasad wrote: > >>> Hi Ingo, > >>> Please accept these patches into the rt tree which convert the > >>> existing RCU tracing mechanism for Preempt RCU and RCU Boost into > >>> markers. > >>> > >>> These patches are based upon the 2.6.24-rc5-rt1 kernel tree. > >>> > >>> Along with marker transition, the RCU Tracing infrastructure has also > >>> been modularised to be built as a kernel module, thereby enabling > >>> runtime changes to the RCU Tracing infrastructure. > >>> > >>> Patch [1/2] - Patch that converts the Preempt RCU tracing in > >>> rcupreempt.c into markers. > >>> > >>> Patch [1/2] - Patch that converts the Preempt RCU Boost tracing in > >>> rcupreempt-boost.c into markers. > >>> > >> I have a technical problem with marker-based RCU tracing: It causes > >> nasty recursions with latest multi-probe marker patches (sorry, no link > >> at hand, can be found in latest LTTng, maybe also already in -mm). Those > >> patches introduce a marker probe trampoline like this: > >> > >> void marker_probe_cb(const struct marker *mdata, void *call_private, > >> const char *fmt, ...) > >> { > >> va_list args; > >> char ptype; > >> > >> /* > >> * rcu_read_lock does two things : disabling preemption to make sure the > >> * teardown of the callbacks can be done correctly when they are in > >> * modules and they insure RCU read coherency. > >> */ > >> rcu_read_lock(); > >> preempt_disable(); > >> ... > >> > >> Can we do multi-probe with pure preempt_disable/enable protection? I > >> guess it's fine with classic RCU, but what about preemptible RCU? Any > >> suggestion appreciated! > > > > If you substitute synchronize_sched() for synchronize_rcu(), this should > > work fine. Of course, this approach would cause RCU tracing to degrade > > latencies somewhat in -rt. > > > > If tracing is using call_rcu(), we will need to add a call_sched() > > or some such. > > You mean something like "#define call_sched call_rcu_classic"? > > I just learned that there is another reason for killing > rcu_read_lock&friends from the marker probes: It can deadlock on -rt > with PREEMPT_RCU_BOOST (hit probe inside rq-lock protected region => > rcu_read_unlock triggers unboost => stuck on rq_lock :( ). > Yep, ok, let's do this : in include/linux/rcupdate.h #ifndef PREEMPT_RT #define call_sched call_rcu #else #define call_sched call_rcu_classic #endif And I'll adapt the markers accordingly. Mathieu > Jan > > -- > Siemens AG, Corporate Technology, CT SE 2 > Corporate Competence Center Embedded Linux -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/