Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751634AbdG0Jzj (ORCPT ); Thu, 27 Jul 2017 05:55:39 -0400 Received: from mail-pg0-f44.google.com ([74.125.83.44]:38904 "EHLO mail-pg0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751454AbdG0JzX (ORCPT ); Thu, 27 Jul 2017 05:55:23 -0400 Subject: Re: Regression with suspicious RCU usage splats with cpu_pm change From: Alex Shi To: "Rafael J. Wysocki" Cc: paulmck@linux.vnet.ibm.com, Tony Lindgren , Linux Kernel Mailing List , Linux PM , Linux OMAP Mailing List , Catalin Marinas , Will Deacon References: <20170713070749.GE16509@atomide.com> <20170713124318.GK2393@linux.vnet.ibm.com> Message-ID: <461af072-9b01-b08b-9ae6-09f14c9b187a@linaro.org> Date: Thu, 27 Jul 2017 17:55:19 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7718 Lines: 241 Hi Rafael, Guess you overlook my new patch in this thread. :) Do I need to recent this patch as new? or you could pick it up here? BTW, it's Tested-by: Tony Lindgren Thanks! Alex On 07/17/2017 07:24 AM, Alex Shi wrote: > > > On 07/13/2017 08:43 PM, Paul E. McKenney wrote: >> On Thu, Jul 13, 2017 at 01:50:26PM +0200, Rafael J. Wysocki wrote: >>> On Thu, Jul 13, 2017 at 11:43 AM, Alex Shi wrote: >>>> >>>> On 07/13/2017 03:07 PM, Tony Lindgren wrote: >>>>> Hi, >>>>> >>>>> Looks like next-20170713 gives me a bunch of "suspicious RCU usage" >>>>> splats with cpuidle_coupled on duovero, see below. I bisected it down >>>>> to commit 2f027e003d05 ("cpu_pm: replace raw_notifier with >>>>> atomic_notifier"). >>> >>> OK, so I'm dropping this commit. >> >> You can surround idle-loop RCU-reading code with RCU_NONIDLE(). >> This will tell RCU to pay attention even though the CPU is otherwise >> idle. >> >> Thanx, Paul >> > > > Thanks a lot, Paul! :) > I reused the rcu_irq_enter_irqson() from RCU_NONIDLE to avoid this issue. > It works fine. > > Tony, Could you like to give a tested-by if this patch works for you. > > Sebastian, > May I keep your acked-by with new fixed patch, since the main thing remained? :) > > > Thanks everyone! > > ====== > > From c8ec81808d46a78e58267f6a23f2b58b48ed5725 Mon Sep 17 00:00:00 2001 > From: Alex Shi > Date: Tue, 4 Jul 2017 21:49:23 +0800 > Subject: [PATCH] cpu_pm: replace raw_notifier to atomic_notifier > > This patch replace a rwlock and raw notifier by atomic notifier which > protected by spin_lock and rcu. > > The first to reason to have this replace is due to a 'scheduling while > atomic' bug of RT kernel on arm/arm64 platform. On arm/arm64, rwlock > cpu_pm_notifier_lock in cpu_pm cause a potential schedule after irq > disable in idle call chain: > > cpu_startup_entry > cpu_idle_loop > local_irq_disable() > cpuidle_idle_call > call_cpuidle > cpuidle_enter > cpuidle_enter_state > ->enter :arm_enter_idle_state > cpu_pm_enter/exit > CPU_PM_CPU_IDLE_ENTER > read_lock(&cpu_pm_notifier_lock); <-- sleep in idle > __rt_spin_lock(); > schedule(); > > The kernel panic is here: > [ 4.609601] BUG: scheduling while atomic: swapper/1/0/0x00000002 > [ 4.609608] [] arm_enter_idle_state+0x18/0x70 > [ 4.609614] Modules linked in: > [ 4.609615] [] cpuidle_enter_state+0xf0/0x218 > [ 4.609620] [] cpuidle_enter+0x18/0x20 > [ 4.609626] Preemption disabled at: > [ 4.609627] [] call_cpuidle+0x24/0x40 > [ 4.609635] [] schedule_preempt_disabled+0x1c/0x28 > [ 4.609639] [] cpu_startup_entry+0x154/0x1f8 > [ 4.609645] [] secondary_start_kernel+0x15c/0x1a0 > > Daniel Lezcano said this notification is needed on arm/arm64 platforms. > Sebastian suggested using atomic_notifier instead of rwlock, which is not > only removing the sleeping in idle, but also getting better latency > improvement. > > Tony Lezcano found a miss use that rcu_read_lock used after rcu_idle_enter > Paul E. McKenney suggested trying RCU_NONIDLE. > > Thanks everyone! :) > > This patch passed Fengguang's 0day testing. > > Signed-off-by: Alex Shi > To: linux-kernel@vger.kernel.org > Cc: Sebastian Andrzej Siewior > Cc: Thomas Gleixner > Cc: Anders Roxell > Cc: Daniel Lezcano > Cc: Rafael J. Wysocki > Cc: Tony Lindgren > Cc: linux-pm@vger.kernel.org > Cc: linux-rt-users > Acked-by: Sebastian Andrzej Siewior > --- > kernel/cpu_pm.c | 50 +++++++++++++------------------------------------- > 1 file changed, 13 insertions(+), 37 deletions(-) > > diff --git a/kernel/cpu_pm.c b/kernel/cpu_pm.c > index 009cc9a..67b02e1 100644 > --- a/kernel/cpu_pm.c > +++ b/kernel/cpu_pm.c > @@ -22,15 +22,21 @@ > #include > #include > > -static DEFINE_RWLOCK(cpu_pm_notifier_lock); > -static RAW_NOTIFIER_HEAD(cpu_pm_notifier_chain); > +static ATOMIC_NOTIFIER_HEAD(cpu_pm_notifier_chain); > > static int cpu_pm_notify(enum cpu_pm_event event, int nr_to_call, int *nr_calls) > { > int ret; > > - ret = __raw_notifier_call_chain(&cpu_pm_notifier_chain, event, NULL, > + /* > + * __atomic_notifier_call_chain has a RCU read critical section, which > + * could be disfunctional in cpu idle. Copy RCU_NONIDLE code to let > + * RCU know this. > + */ > + rcu_irq_enter_irqson(); > + ret = __atomic_notifier_call_chain(&cpu_pm_notifier_chain, event, NULL, > nr_to_call, nr_calls); > + rcu_irq_exit_irqson(); > > return notifier_to_errno(ret); > } > @@ -47,14 +53,7 @@ static int cpu_pm_notify(enum cpu_pm_event event, int nr_to_call, int *nr_calls) > */ > int cpu_pm_register_notifier(struct notifier_block *nb) > { > - unsigned long flags; > - int ret; > - > - write_lock_irqsave(&cpu_pm_notifier_lock, flags); > - ret = raw_notifier_chain_register(&cpu_pm_notifier_chain, nb); > - write_unlock_irqrestore(&cpu_pm_notifier_lock, flags); > - > - return ret; > + return atomic_notifier_chain_register(&cpu_pm_notifier_chain, nb); > } > EXPORT_SYMBOL_GPL(cpu_pm_register_notifier); > > @@ -69,14 +68,7 @@ EXPORT_SYMBOL_GPL(cpu_pm_register_notifier); > */ > int cpu_pm_unregister_notifier(struct notifier_block *nb) > { > - unsigned long flags; > - int ret; > - > - write_lock_irqsave(&cpu_pm_notifier_lock, flags); > - ret = raw_notifier_chain_unregister(&cpu_pm_notifier_chain, nb); > - write_unlock_irqrestore(&cpu_pm_notifier_lock, flags); > - > - return ret; > + return atomic_notifier_chain_unregister(&cpu_pm_notifier_chain, nb); > } > EXPORT_SYMBOL_GPL(cpu_pm_unregister_notifier); > > @@ -100,7 +92,6 @@ int cpu_pm_enter(void) > int nr_calls; > int ret = 0; > > - read_lock(&cpu_pm_notifier_lock); > ret = cpu_pm_notify(CPU_PM_ENTER, -1, &nr_calls); > if (ret) > /* > @@ -108,7 +99,6 @@ int cpu_pm_enter(void) > * PM entry who are notified earlier to prepare for it. > */ > cpu_pm_notify(CPU_PM_ENTER_FAILED, nr_calls - 1, NULL); > - read_unlock(&cpu_pm_notifier_lock); > > return ret; > } > @@ -128,13 +118,7 @@ EXPORT_SYMBOL_GPL(cpu_pm_enter); > */ > int cpu_pm_exit(void) > { > - int ret; > - > - read_lock(&cpu_pm_notifier_lock); > - ret = cpu_pm_notify(CPU_PM_EXIT, -1, NULL); > - read_unlock(&cpu_pm_notifier_lock); > - > - return ret; > + return cpu_pm_notify(CPU_PM_EXIT, -1, NULL); > } > EXPORT_SYMBOL_GPL(cpu_pm_exit); > > @@ -159,7 +143,6 @@ int cpu_cluster_pm_enter(void) > int nr_calls; > int ret = 0; > > - read_lock(&cpu_pm_notifier_lock); > ret = cpu_pm_notify(CPU_CLUSTER_PM_ENTER, -1, &nr_calls); > if (ret) > /* > @@ -167,7 +150,6 @@ int cpu_cluster_pm_enter(void) > * PM entry who are notified earlier to prepare for it. > */ > cpu_pm_notify(CPU_CLUSTER_PM_ENTER_FAILED, nr_calls - 1, NULL); > - read_unlock(&cpu_pm_notifier_lock); > > return ret; > } > @@ -190,13 +172,7 @@ EXPORT_SYMBOL_GPL(cpu_cluster_pm_enter); > */ > int cpu_cluster_pm_exit(void) > { > - int ret; > - > - read_lock(&cpu_pm_notifier_lock); > - ret = cpu_pm_notify(CPU_CLUSTER_PM_EXIT, -1, NULL); > - read_unlock(&cpu_pm_notifier_lock); > - > - return ret; > + return cpu_pm_notify(CPU_CLUSTER_PM_EXIT, -1, NULL); > } > EXPORT_SYMBOL_GPL(cpu_cluster_pm_exit); > >