Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756324AbYBIRPG (ORCPT ); Sat, 9 Feb 2008 12:15:06 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754296AbYBIRO4 (ORCPT ); Sat, 9 Feb 2008 12:14:56 -0500 Received: from mtagate7.uk.ibm.com ([195.212.29.140]:64355 "EHLO mtagate7.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754013AbYBIROy (ORCPT ); Sat, 9 Feb 2008 12:14:54 -0500 Date: Sat, 9 Feb 2008 18:14:51 +0100 From: Heiko Carstens To: "Paul E. McKenney" Cc: Gautham R Shenoy , Dipankar Sarma , Steven Rostedt , Ingo Molnar , Martin Schwidefsky , linux-kernel@vger.kernel.org Subject: Re: preempt rcu bug on s390 Message-ID: <20080209171451.GB8069@osiris.ibm.com> References: <20080209113435.GA6915@osiris.boeblingen.de.ibm.com> <20080209140711.GA16205@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080209140711.GA16205@linux.vnet.ibm.com> User-Agent: Mutt/1.5.16 (2007-06-09) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3479 Lines: 96 On Sat, Feb 09, 2008 at 06:07:11AM -0800, Paul E. McKenney wrote: > On Sat, Feb 09, 2008 at 12:34:35PM +0100, Heiko Carstens wrote: > > Using CONFIG_PREEMPT_RCU and CONFIG_NO_IDLE_HZ on s390 my system always > > gets stuck when running with more than one cpu. > > When booting with four cpus I get all four cpus caught withing cpu_idle > > and not advancing anymore. However there is the init process which is > > waitung for synchronize_rcu() to complete (lcrash output): > > > > STACK TRACE FOR TASK: 0xf84d968 (swapper) > > > > STACK: > > 0 schedule+842 [0x36c956] > > 1 schedule_timeout+172 [0x36d0e4] > > 2 wait_for_common+204 [0x36c398] > > 3 synchronize_rcu+76 [0x567bc] > > 4 netlink_change_ngroups+150 [0x2b4302] > > 5 genl_register_mc_group+256 [0x2b6174] > > 6 genl_init+188 [0x534e44] > > 7 kernel_init+444 [0x518334] > > 8 kernel_thread_starter+6 [0x192a6] > > > > If I change the code so that timer ticks won't be disabled everything > > runs fine. So my guess is that rcu_needs_cpu() doesn't do the right > > thing for the rcu preemptible case. > > > > Kernel version is git head of today. > > > > Any ideas? > > Does this tree have http://lkml.org/lkml/2008/1/29/208 applied? > > If not, could you please check it out? It's not applied, however it doesn't change anything. Also the patch is tied to the dynticks implementation which is differently from s390's nohz implementation. I had to add the patch below so it would make at least some sense. But it doesn't fix the problem. --- arch/s390/kernel/time.c | 2 ++ include/linux/hardirq.h | 2 +- kernel/rcupreempt.c | 2 +- 3 files changed, 4 insertions(+), 2 deletions(-) Index: linux-2.6/kernel/rcupreempt.c =================================================================== --- linux-2.6.orig/kernel/rcupreempt.c +++ linux-2.6/kernel/rcupreempt.c @@ -413,7 +413,7 @@ static void __rcu_advance_callbacks(stru } } -#ifdef CONFIG_NO_HZ +#if defined(CONFIG_NO_HZ) || defined(CONFIG_NO_IDLE_HZ) DEFINE_PER_CPU(long, dynticks_progress_counter) = 1; static DEFINE_PER_CPU(long, rcu_dyntick_snapshot); Index: linux-2.6/arch/s390/kernel/time.c =================================================================== --- linux-2.6.orig/arch/s390/kernel/time.c +++ linux-2.6/arch/s390/kernel/time.c @@ -200,6 +200,7 @@ static void stop_hz_timer(void) if (timer >= jiffies_timer_cc) todval = timer; } + rcu_enter_nohz(); set_clock_comparator(todval); } @@ -213,6 +214,7 @@ static void start_hz_timer(void) if (!cpu_isset(smp_processor_id(), nohz_cpu_mask)) return; + rcu_exit_nohz(); account_ticks(get_clock()); set_clock_comparator(S390_lowcore.jiffy_timer + CPU_DEVIATION); cpu_clear(smp_processor_id(), nohz_cpu_mask); Index: linux-2.6/include/linux/hardirq.h =================================================================== --- linux-2.6.orig/include/linux/hardirq.h +++ linux-2.6/include/linux/hardirq.h @@ -109,7 +109,7 @@ static inline void account_system_vtime( } #endif -#if defined(CONFIG_PREEMPT_RCU) && defined(CONFIG_NO_HZ) +#if defined(CONFIG_PREEMPT_RCU) && (defined(CONFIG_NO_HZ) || defined(CONFIG_NO_IDLE_HZ)) extern void rcu_irq_enter(void); extern void rcu_irq_exit(void); #else -- 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/