Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932071Ab1BWSkX (ORCPT ); Wed, 23 Feb 2011 13:40:23 -0500 Received: from blu0-omc1-s26.blu0.hotmail.com ([65.55.116.37]:19692 "EHLO blu0-omc1-s26.blu0.hotmail.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754318Ab1BWSkW (ORCPT ); Wed, 23 Feb 2011 13:40:22 -0500 X-Originating-IP: [174.91.193.52] X-Originating-Email: [pdumas9@sympatico.ca] Message-ID: Date: Wed, 23 Feb 2011 13:40:17 -0500 From: Mathieu Desnoyers To: "Paul E. McKenney" CC: Steven Rostedt , linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com Subject: Re: [PATCH] debug rcu head support !PREEMPT config References: <20110223013917.GA20996@linux.vnet.ibm.com> <1298425183-21265-5-git-send-email-paulmck@linux.vnet.ibm.com> <1298431409.7666.76.camel@gandalf.stny.rr.com> <1298472914.7666.85.camel@gandalf.stny.rr.com> <1298474827.7666.86.camel@gandalf.stny.rr.com> <20110223183109.GO2163@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: <20110223183109.GO2163@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: 13:39:57 up 322 days, 4:29, 6 users, load average: 2.15, 1.97, 1.90 User-Agent: Mutt/1.5.18 (2008-05-17) X-OriginalArrivalTime: 23 Feb 2011 18:40:20.0753 (UTC) FILETIME=[1FCA6810:01CBD389] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4348 Lines: 99 * Paul E. McKenney (paulmck@linux.vnet.ibm.com) wrote: > On Wed, Feb 23, 2011 at 10:37:26AM -0500, Mathieu Desnoyers wrote: > > * Steven Rostedt (rostedt@goodmis.org) wrote: > > > On Wed, 2011-02-23 at 10:13 -0500, Mathieu Desnoyers wrote: > > > > Remove DEBUG_RCU_HEAD dependency on PREEMPT config. Handle the unability to > > > > detect if within a RCU read-side critical section by never performing any > > > > attempt to recover from a failure situation in the fixup handlers. Just print > > > > the warnings. > > > > > > > > This patch is only compile-tested. > > > > > > > > Signed-off-by: Mathieu Desnoyers > > > > --- > > > > kernel/rcupdate.c | 17 +++++++++++++++++ > > > > lib/Kconfig.debug | 2 +- > > > > 2 files changed, 18 insertions(+), 1 deletion(-) > > > > > > > > Index: linux-2.6-lttng/lib/Kconfig.debug > > > > =================================================================== > > > > --- linux-2.6-lttng.orig/lib/Kconfig.debug > > > > +++ linux-2.6-lttng/lib/Kconfig.debug > > > > @@ -313,7 +313,7 @@ config DEBUG_OBJECTS_WORK > > > > > > > > config DEBUG_OBJECTS_RCU_HEAD > > > > bool "Debug RCU callbacks objects" > > > > - depends on DEBUG_OBJECTS && PREEMPT > > > > + depends on DEBUG_OBJECTS > > > > help > > > > Enable this to turn on debugging of RCU list heads (call_rcu() usage). > > > > > > > > Index: linux-2.6-lttng/kernel/rcupdate.c > > > > =================================================================== > > > > --- linux-2.6-lttng.orig/kernel/rcupdate.c > > > > +++ linux-2.6-lttng/kernel/rcupdate.c > > > > @@ -142,7 +142,14 @@ static int rcuhead_fixup_init(void *addr > > > > * Ensure that queued callbacks are all executed. > > > > * If we detect that we are nested in a RCU read-side critical > > > > * section, we should simply fail, otherwise we would deadlock. > > > > + * In !PREEMPT configurations, there is no way to tell if we are > > > > + * in a RCU read-side critical section or not, so we never > > > > + * attempt any fixup and just print a warning. > > > > */ > > > > +#ifndef CONFIG_PREEMPT > > > > + WARN_ON(1); > > > > + return 0; > > > > +#endif > > > > if (rcu_preempt_depth() != 0 || preempt_count() != 0 || > > > > irqs_disabled()) { > > > > WARN_ON(1); > > > > @@ -184,7 +191,14 @@ static int rcuhead_fixup_activate(void * > > > > * Ensure that queued callbacks are all executed. > > > > * If we detect that we are nested in a RCU read-side critical > > > > * section, we should simply fail, otherwise we would deadlock. > > > > + * In !PREEMPT configurations, there is no way to tell if we are > > > > + * in a RCU read-side critical section or not, so we never > > > > + * attempt any fixup and just print a warning. > > > > */ > > > > +#ifndef CONFIG_PREEMPT > > > > + WARN_ON(1); > > > > + return 0; > > > > +#endif > > > > if (rcu_preempt_depth() != 0 || preempt_count() != 0 || > > > > irqs_disabled()) { > > > > WARN_ON(1); > > > > @@ -214,6 +228,9 @@ static int rcuhead_fixup_free(void *addr > > > > * Ensure that queued callbacks are all executed. > > > > * If we detect that we are nested in a RCU read-side critical > > > > * section, we should simply fail, otherwise we would deadlock. > > > > + * In !PREEMPT configurations, there is no way to tell if we are > > > > + * in a RCU read-side critical section or not, so we never > > > > + * attempt any fixup and just print a warning. > > > > */ > > > > #ifndef CONFIG_PREEMPT > > > > WARN_ON(1); > > > > > > Hmm, I wonder if s/WARN_ON/WARN_ON_ONCE/g is in order. Why spam the > > > console if it happens to trigger all the time? > > > > The system should die pretty soon anyway due to list corruption, so I > > don't think it's a problem in practice. > > Well, it would add noise, so I added a patch converting the WARN_ON's > to WARN_ON_ONCE's. Thinking about it, it makes a lot of sense. Thanks! Mathieu -- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com -- 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/