Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754861Ab1BWSbP (ORCPT ); Wed, 23 Feb 2011 13:31:15 -0500 Received: from e8.ny.us.ibm.com ([32.97.182.138]:59358 "EHLO e8.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752198Ab1BWSbN (ORCPT ); Wed, 23 Feb 2011 13:31:13 -0500 Date: Wed, 23 Feb 2011 10:31:09 -0800 From: "Paul E. McKenney" To: Mathieu Desnoyers 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 Message-ID: <20110223183109.GO2163@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3982 Lines: 89 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. Thanx, Paul -- 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/