From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933268AbdGKOmN (ORCPT ); Tue, 11 Jul 2017 10:42:13 -0400 Received: from mail-pf0-f182.google.com ([209.85.192.182]:32774 "EHLO mail-pf0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933172AbdGKOmK (ORCPT ); Tue, 11 Jul 2017 10:42:10 -0400 Subject: Re: [PATCH] cpu_pm: replace raw_notifier to atomic_notifier To: open list Cc: Sebastian Andrzej Siewior , Thomas Gleixner , Anders Roxell , Rik van Riel , Steven Rostedt , "Rafael J . Wysocki" , Daniel Lezcano , linux-rt-users References: <1499330866-19520-1-git-send-email-alex.shi@linaro.org> From: Alex Shi Message-ID: <6cbcde77-8911-8439-9603-b2c1ae1dc595@linaro.org> Date: Tue, 11 Jul 2017 22:42:04 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.1 MIME-Version: 1.0 In-Reply-To: <1499330866-19520-1-git-send-email-alex.shi@linaro.org> 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 It is a serious bug: add a waiting lock in idle and cause boot failure in arm/arm64 RT. Any more comments for this change? On 07/06/2017 04:47 PM, Alex Shi wrote: > 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. > > This patch passed Fengguang's 0day testing. > > Signed-off-by: Alex Shi > Cc: Sebastian Andrzej Siewior > Cc: Thomas Gleixner > Cc: Anders Roxell > Cc: Rik van Riel > Cc: Steven Rostedt > Cc: Rafael J. Wysocki > Cc: Daniel Lezcano > Cc: linux-rt-users > --- > kernel/cpu_pm.c | 43 ++++++------------------------------------- > 1 file changed, 6 insertions(+), 37 deletions(-) > > diff --git a/kernel/cpu_pm.c b/kernel/cpu_pm.c > index 009cc9a..10f4640 100644 > --- a/kernel/cpu_pm.c > +++ b/kernel/cpu_pm.c > @@ -22,14 +22,13 @@ > #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, > + ret = __atomic_notifier_call_chain(&cpu_pm_notifier_chain, event, NULL, > nr_to_call, nr_calls); > > return notifier_to_errno(ret); > @@ -47,14 +46,7 @@ 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 +61,7 @@ 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 +85,6 @@ 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 +92,6 @@ 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 +111,7 @@ 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 +136,6 @@ 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 +143,6 @@ 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 +165,7 @@ 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); > >