From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751910Ab1GSWlp (ORCPT ); Tue, 19 Jul 2011 18:41:45 -0400 Received: from e8.ny.us.ibm.com ([32.97.182.138]:59431 "EHLO e8.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751307Ab1GSWlo (ORCPT ); Tue, 19 Jul 2011 18:41:44 -0400 Date: Tue, 19 Jul 2011 15:41:42 -0700 From: "Paul E. McKenney" To: kernelmail.jms@gmail.com, kulkarni.ravi4@gmail.com Cc: linux-kernel@vger.kernel.org, cmm@us.ibm.com Subject: Fw: RCU boot debug patch Message-ID: <20110719224142.GT2357@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline 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 Hello, Julie and Ravi, Although we arrived at a patch that worked for both of you, we never did identify exactly which RCU callback (or other issue) that was causing the problem. It would be good to do this in case there is some other problem lurking that might bite us in the future. Mingming has therefore put together the following diagnostic patch which should identify the callbacks, please see below. So could you please run this and let us know what you find? There should at least be a message for artificial_callback(). Thanx, Paul ------------------------------------------------------------------------ A debug patch to verify if there is RCU callbacks before the rcu scheduler is active. Please looking at the dmesg to see if any message print out related to this other than the artificial one. Signed_off_by: Mingming Cao diff --git a/init/main.c b/init/main.c index d7211fa..2abc1a5 100644 --- a/init/main.c +++ b/init/main.c @@ -452,11 +452,13 @@ static void __init mm_init(void) pgtable_cache_init(); vmalloc_init(); } +static void artificial_callback(struct rcu_head *p) {}; asmlinkage void __init start_kernel(void) { char * command_line; extern const struct kernel_param __start___param[], __stop___param[]; + static struct rcu_head artificial_rcu_head; smp_setup_processor_id(); @@ -531,6 +533,7 @@ asmlinkage void __init start_kernel(void) idr_init_cache(); perf_event_init(); rcu_init(); + call_rcu(&artificial_rcu_head, artificial_callback); radix_tree_init(); /* init some links before init_ISA_irqs() */ early_irq_init(); diff --git a/kernel/rcutree.c b/kernel/rcutree.c index ba06207..60ca927 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1514,6 +1514,11 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), head->func = func; head->next = NULL; + if ((system_state == SYSTEM_BOOTING) && (!rcu_scheduler_active)) + printk(KERN_ALERT "RCU scheduler is not active yet, " + "Calling _call_rcu() with this function %pf\n", + func); + smp_mb(); /* Ensure RCU update seen before callback registry. */ /*