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PM / CPU: replace raw_notifier with atomic_notifier

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This patch replaces an rwlock and raw notifier by an atomic notifier
protected by a spin_lock and RCU.

The main reason for this change is due to a 'scheduling while atomic'
bug with RT kernels on ARM/ARM64. On ARM/ARM64, the rwlock
cpu_pm_notifier_lock in cpu_pm_enter/exit() causes a potential
schedule after IRQ disable in the 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.
Sebastian suggested using atomic_notifier instead of rwlock, which is not
only removing the sleeping in idle, but also improving latency.

Tony Lindgren found a miss use that rcu_read_lock used after rcu_idle_enter
Paul McKenney suggested trying RCU_NONIDLE.

Signed-off-by: Alex Shi <alex.shi@linaro.org>
Tested-by: Tony Lindgren <tony@atomide.com>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
[ rjw: Subject & changelog ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Alex Shi 2017-07-28 15:09:25 +08:00 committed by Rafael J. Wysocki
parent 16f73eb02d
commit 313c8c16ee
1 changed files with 13 additions and 37 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

50
kernel/cpu_pm.c
View file

@ -22,15 +22,21 @@
#include <linux/spinlock.h>
#include <linux/syscore_ops.h>
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);