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Date: Fri, 16 Jun 2017 11:12:57 +0800
From: Alex Shi <alex.shi@...aro.org>
To: open list <linux-kernel@...r.kernel.org>,
linux-rt-users <linux-rt-users@...r.kernel.org>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Thomas Gleixner <tglx@...utronix.de>,
Anders Roxell <anders.roxell@...aro.org>,
Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [RFC PATCH] cpu_pm/rt: replace rt rwlock with raw spinlock
It's a serious bug which cause arm/arm64 rt boot failed.
Anyone like to give a glance?
Thanks
Alex
On 06/14/2017 09:22 PM, Alex Shi wrote:
> This is a quick fix for a bug as 'scheduling while atomic' or
> 'scheduling from the idle thread' on arm/arm64.
>
> 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] [<ffff0000086fae70>] arm_enter_idle_state+0x18/0x70
> [ 4.609614] Modules linked in:
> [ 4.609615] [<ffff0000086f9298>] cpuidle_enter_state+0xf0/0x218
> [ 4.609620] [<ffff0000086f93f8>] cpuidle_enter+0x18/0x20
> [ 4.609626] Preemption disabled at:
> [ 4.609627] [<ffff0000080fa234>] call_cpuidle+0x24/0x40
> [ 4.609635] [<ffff000008882fa4>] schedule_preempt_disabled+0x1c/0x28
> [ 4.609639] [<ffff0000080fa49c>] cpu_startup_entry+0x154/0x1f8
> [ 4.609645] [<ffff00000808e004>] secondary_start_kernel+0x15c/0x1a0
>
> Daniel Lezcano said this notification is needed on arm/arm64 platforms.
> I also tried use local_lock_irq to replace local_irq_disable, but my 2
> boards just die without any output. So maybe it's only quick way to
> make rt kernel work on arm/arm64.
>
> Since this is quick fix, instead of split out the raw rwlock, to use
> raw_spin_lock is simple and don't cost much.
>
> Signed-off-by: Alex Shi <alex.shi@...aro.org>
> Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Anders Roxell <anders.roxell@...aro.org>
> Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
> Cc: linux-rt-users <linux-rt-users@...r.kernel.org>
> ---
> kernel/cpu_pm.c | 26 +++++++++++++-------------
> 1 file changed, 13 insertions(+), 13 deletions(-)
>
> diff --git a/kernel/cpu_pm.c b/kernel/cpu_pm.c
> index 009cc9a..8ffa13e3 100644
> --- a/kernel/cpu_pm.c
> +++ b/kernel/cpu_pm.c
> @@ -22,7 +22,7 @@
> #include <linux/spinlock.h>
> #include <linux/syscore_ops.h>
>
> -static DEFINE_RWLOCK(cpu_pm_notifier_lock);
> +static DEFINE_RAW_SPINLOCK(cpu_pm_notifier_lock);
> static RAW_NOTIFIER_HEAD(cpu_pm_notifier_chain);
>
> static int cpu_pm_notify(enum cpu_pm_event event, int nr_to_call, int *nr_calls)
> @@ -50,9 +50,9 @@ int cpu_pm_register_notifier(struct notifier_block *nb)
> unsigned long flags;
> int ret;
>
> - write_lock_irqsave(&cpu_pm_notifier_lock, flags);
> + raw_spin_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);
> + raw_spin_unlock_irqrestore(&cpu_pm_notifier_lock, flags);
>
> return ret;
> }
> @@ -72,9 +72,9 @@ int cpu_pm_unregister_notifier(struct notifier_block *nb)
> unsigned long flags;
> int ret;
>
> - write_lock_irqsave(&cpu_pm_notifier_lock, flags);
> + raw_spin_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);
> + raw_spin_unlock_irqrestore(&cpu_pm_notifier_lock, flags);
>
> return ret;
> }
> @@ -100,7 +100,7 @@ int cpu_pm_enter(void)
> int nr_calls;
> int ret = 0;
>
> - read_lock(&cpu_pm_notifier_lock);
> + raw_spin_lock(&cpu_pm_notifier_lock);
> ret = cpu_pm_notify(CPU_PM_ENTER, -1, &nr_calls);
> if (ret)
> /*
> @@ -108,7 +108,7 @@ 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);
> + raw_spin_unlock(&cpu_pm_notifier_lock);
>
> return ret;
> }
> @@ -130,9 +130,9 @@ int cpu_pm_exit(void)
> {
> int ret;
>
> - read_lock(&cpu_pm_notifier_lock);
> + raw_spin_lock(&cpu_pm_notifier_lock);
> ret = cpu_pm_notify(CPU_PM_EXIT, -1, NULL);
> - read_unlock(&cpu_pm_notifier_lock);
> + raw_spin_unlock(&cpu_pm_notifier_lock);
>
> return ret;
> }
> @@ -159,7 +159,7 @@ int cpu_cluster_pm_enter(void)
> int nr_calls;
> int ret = 0;
>
> - read_lock(&cpu_pm_notifier_lock);
> + raw_spin_lock(&cpu_pm_notifier_lock);
> ret = cpu_pm_notify(CPU_CLUSTER_PM_ENTER, -1, &nr_calls);
> if (ret)
> /*
> @@ -167,7 +167,7 @@ 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);
> + raw_spin_unlock(&cpu_pm_notifier_lock);
>
> return ret;
> }
> @@ -192,9 +192,9 @@ int cpu_cluster_pm_exit(void)
> {
> int ret;
>
> - read_lock(&cpu_pm_notifier_lock);
> + raw_spin_lock(&cpu_pm_notifier_lock);
> ret = cpu_pm_notify(CPU_CLUSTER_PM_EXIT, -1, NULL);
> - read_unlock(&cpu_pm_notifier_lock);
> + raw_spin_unlock(&cpu_pm_notifier_lock);
>
> return ret;
> }
>
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