From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753429AbZHFB0q (ORCPT ); Wed, 5 Aug 2009 21:26:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752796AbZHFB0p (ORCPT ); Wed, 5 Aug 2009 21:26:45 -0400 Received: from e7.ny.us.ibm.com ([32.97.182.137]:34625 "EHLO e7.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752740AbZHFB0o (ORCPT ); Wed, 5 Aug 2009 21:26:44 -0400 Date: Wed, 5 Aug 2009 18:26:45 -0700 From: "Paul E. McKenney" To: Ingo Molnar Cc: mingo@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org, tglx@linutronix.de, linux-tip-commits@vger.kernel.org, ego@in.ibm.com Subject: Re: [tip:core/rcu] rcu: Add diagnostic check for a possible CPU-hotplug race Message-ID: <20090806012645.GA24800@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20090802202720.GA32360@elte.hu> <20090802221324.GP6854@linux.vnet.ibm.com> <20090803070458.GA27581@elte.hu> <20090803125618.GV6854@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090803125618.GV6854@linux.vnet.ibm.com> User-Agent: Mutt/1.5.15+20070412 (2007-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 03, 2009 at 05:56:18AM -0700, Paul E. McKenney wrote: > On Mon, Aug 03, 2009 at 09:04:58AM +0200, Ingo Molnar wrote: > > > > i've attached the full serial bootlog with the warning in it. This > > should address your question about what the order of initialization > > is, right? > > It does, thank you! This problem really is happening during boot. > > > Let me know if you still would like me to run your diagnostic patch > > too. > > Now that you mention it, you should probably let me test it a bit first. And here is a tested and debugged version. Diagnostic only, not for inclusion, based on tip/core/rcu as of today (August 5th). Gautham, have you been able to reproduce on your machines? Still cannot here. Thanx, Paul ------------------------------------------------------------------------ Create an rcu_cpu_notified() API that checks to see whether RCU's CPU-hotplug notifier is registered. This is used in three WARN_ON_ONCE() calls, the first of which should trigger, and the second two of which should not -- but I suspect that the WARN_ON_ONCE() located in __rcu_process_callbacks() will in fact trigger on the machine suffering from this bug. ;-) Any code path that executes after rcu_init() should have RCU CPU-hotplug notifiers registered, so any triggering of the following WARN_ON_ONCE() after rcu_init() is a bug: WARN_ON_ONCE(!rcu_cpu_notified()); Signed-off-by: Paul E. McKenney --- include/linux/cpu.h | 3 +++ include/linux/rcupdate.h | 1 + kernel/cpu.c | 5 +++++ kernel/notifier.c | 23 +++++++++++++++++++++++ kernel/rcupdate.c | 9 ++++++++- kernel/rcutree.c | 1 + 6 files changed, 41 insertions(+), 1 deletion(-) diff --git a/include/linux/cpu.h b/include/linux/cpu.h index 4d668e0..d9b3c18 100644 --- a/include/linux/cpu.h +++ b/include/linux/cpu.h @@ -51,6 +51,9 @@ struct notifier_block; #ifdef CONFIG_HOTPLUG_CPU extern int register_cpu_notifier(struct notifier_block *nb); extern void unregister_cpu_notifier(struct notifier_block *nb); +extern int cpu_notified(int (*fn)(struct notifier_block *, unsigned long, void *)); +extern int raw_notifier_chain_is_registered(struct raw_notifier_head *nh, + int (*fn)(struct notifier_block *, unsigned long, void *)); #else #ifndef MODULE diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 3c89d6a..f790f3c 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -65,6 +65,7 @@ extern void rcu_init(void); extern void rcu_scheduler_starting(void); extern int rcu_needs_cpu(int cpu); extern int rcu_scheduler_active; +extern int rcu_cpu_notified(void); #if defined(CONFIG_TREE_RCU) #include diff --git a/kernel/cpu.c b/kernel/cpu.c index 8ce1004..5aa736a 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -133,6 +133,11 @@ int __ref register_cpu_notifier(struct notifier_block *nb) return ret; } +int cpu_notified(int (*fn)(struct notifier_block *, unsigned long, void *)) +{ + return raw_notifier_chain_is_registered(&cpu_chain, fn); +} + #ifdef CONFIG_HOTPLUG_CPU EXPORT_SYMBOL(register_cpu_notifier); diff --git a/kernel/notifier.c b/kernel/notifier.c index 61d5aa5..d72c0b8 100644 --- a/kernel/notifier.c +++ b/kernel/notifier.c @@ -59,6 +59,29 @@ static int notifier_chain_unregister(struct notifier_block **nl, return -ENOENT; } +static int notifier_chain_is_registered(struct notifier_block *nl, + int (*fn)(struct notifier_block *, unsigned long, void *)) +{ + rcu_read_lock(); + /* printk(KERN_ALERT "notifier_chain_is_registered looking for: %pS\n", fn); */ + while (nl != NULL) { + /* printk(KERN_ALERT "notifier_chain_is_registered: %pS\n", rcu_dereference(nl)->notifier_call); */ + if (rcu_dereference(nl)->notifier_call == fn) { + rcu_read_unlock(); + return 1; + } + nl = (rcu_dereference(nl)->next); + } + rcu_read_unlock(); + return 0; +} + +int raw_notifier_chain_is_registered(struct raw_notifier_head *nh, + int (*fn)(struct notifier_block *, unsigned long, void *)) +{ + return notifier_chain_is_registered(nh->head, fn); +} + /** * notifier_call_chain - Informs the registered notifiers about an event. * @nl: Pointer to head of the blocking notifier chain diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index 9f0584e..57a4626 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -220,7 +220,7 @@ static void rcu_migrate_callback(struct rcu_head *notused) extern int rcu_cpu_notify(struct notifier_block *self, unsigned long action, void *hcpu); -static int __cpuinit rcu_barrier_cpu_hotplug(struct notifier_block *self, +int __cpuinit rcu_barrier_cpu_hotplug(struct notifier_block *self, unsigned long action, void *hcpu) { rcu_cpu_notify(self, action, hcpu); @@ -246,12 +246,19 @@ static int __cpuinit rcu_barrier_cpu_hotplug(struct notifier_block *self, return NOTIFY_OK; } +int rcu_cpu_notified(void) +{ + return cpu_notified(rcu_barrier_cpu_hotplug); +} + void __init rcu_init(void) { int i; __rcu_init(); + WARN_ON_ONCE(!rcu_cpu_notified()); /* this one expected to trigger. */ hotcpu_notifier(rcu_barrier_cpu_hotplug, 0); + WARN_ON_ONCE(!rcu_cpu_notified()); /* * We don't need protection against CPU-hotplug here because diff --git a/kernel/rcutree.c b/kernel/rcutree.c index b9b1928..a0bfc93 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1133,6 +1133,7 @@ __rcu_process_callbacks(struct rcu_state *rsp, struct rcu_data *rdp) unsigned long flags; WARN_ON_ONCE(rdp->beenonline == 0); + WARN_ON_ONCE(!rcu_cpu_notified()); /* * If an RCU GP has gone long enough, go check for dyntick