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![Valentin Schneider](/assets/img/avatar_default.png)
Invoking atomic_notifier_chain_notify() requires acquiring a spinlock_t,
which can block under CONFIG_PREEMPT_RT. Notifications for members of the
cpu_pm notification chain will be issued by the idle task, which can never
block.
Making *all* atomic_notifiers use a raw_spinlock is too big of a hammer, as
only notifications issued by the idle task are problematic.
Special-case cpu_pm_notifier_chain by kludging a raw_notifier and
raw_spinlock_t together, matching the atomic_notifier behavior with a
raw_spinlock_t.
Fixes: 70d9329857
("notifier: Fix broken error handling pattern")
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
214 lines
6.1 KiB
C
214 lines
6.1 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Copyright (C) 2011 Google, Inc.
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*
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* Author:
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* Colin Cross <ccross@android.com>
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*/
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#include <linux/kernel.h>
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#include <linux/cpu_pm.h>
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#include <linux/module.h>
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#include <linux/notifier.h>
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#include <linux/spinlock.h>
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#include <linux/syscore_ops.h>
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/*
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* atomic_notifiers use a spinlock_t, which can block under PREEMPT_RT.
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* Notifications for cpu_pm will be issued by the idle task itself, which can
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* never block, IOW it requires using a raw_spinlock_t.
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*/
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static struct {
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struct raw_notifier_head chain;
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raw_spinlock_t lock;
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} cpu_pm_notifier = {
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.chain = RAW_NOTIFIER_INIT(cpu_pm_notifier.chain),
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.lock = __RAW_SPIN_LOCK_UNLOCKED(cpu_pm_notifier.lock),
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};
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static int cpu_pm_notify(enum cpu_pm_event event)
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{
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int ret;
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/*
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* This introduces a RCU read critical section, which could be
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* disfunctional in cpu idle. Copy RCU_NONIDLE code to let RCU know
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* this.
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*/
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rcu_irq_enter_irqson();
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rcu_read_lock();
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ret = raw_notifier_call_chain(&cpu_pm_notifier.chain, event, NULL);
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rcu_read_unlock();
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rcu_irq_exit_irqson();
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return notifier_to_errno(ret);
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}
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static int cpu_pm_notify_robust(enum cpu_pm_event event_up, enum cpu_pm_event event_down)
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{
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unsigned long flags;
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int ret;
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rcu_irq_enter_irqson();
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raw_spin_lock_irqsave(&cpu_pm_notifier.lock, flags);
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ret = raw_notifier_call_chain_robust(&cpu_pm_notifier.chain, event_up, event_down, NULL);
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raw_spin_unlock_irqrestore(&cpu_pm_notifier.lock, flags);
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rcu_irq_exit_irqson();
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return notifier_to_errno(ret);
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}
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/**
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* cpu_pm_register_notifier - register a driver with cpu_pm
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* @nb: notifier block to register
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*
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* Add a driver to a list of drivers that are notified about
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* CPU and CPU cluster low power entry and exit.
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*
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* This function has the same return conditions as raw_notifier_chain_register.
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*/
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int cpu_pm_register_notifier(struct notifier_block *nb)
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{
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unsigned long flags;
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int ret;
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raw_spin_lock_irqsave(&cpu_pm_notifier.lock, flags);
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ret = raw_notifier_chain_register(&cpu_pm_notifier.chain, nb);
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raw_spin_unlock_irqrestore(&cpu_pm_notifier.lock, flags);
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return ret;
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}
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EXPORT_SYMBOL_GPL(cpu_pm_register_notifier);
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/**
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* cpu_pm_unregister_notifier - unregister a driver with cpu_pm
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* @nb: notifier block to be unregistered
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*
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* Remove a driver from the CPU PM notifier list.
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*
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* This function has the same return conditions as raw_notifier_chain_unregister.
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*/
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int cpu_pm_unregister_notifier(struct notifier_block *nb)
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{
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unsigned long flags;
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int ret;
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raw_spin_lock_irqsave(&cpu_pm_notifier.lock, flags);
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ret = raw_notifier_chain_unregister(&cpu_pm_notifier.chain, nb);
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raw_spin_unlock_irqrestore(&cpu_pm_notifier.lock, flags);
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return ret;
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}
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EXPORT_SYMBOL_GPL(cpu_pm_unregister_notifier);
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/**
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* cpu_pm_enter - CPU low power entry notifier
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*
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* Notifies listeners that a single CPU is entering a low power state that may
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* cause some blocks in the same power domain as the cpu to reset.
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*
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* Must be called on the affected CPU with interrupts disabled. Platform is
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* responsible for ensuring that cpu_pm_enter is not called twice on the same
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* CPU before cpu_pm_exit is called. Notified drivers can include VFP
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* co-processor, interrupt controller and its PM extensions, local CPU
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* timers context save/restore which shouldn't be interrupted. Hence it
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* must be called with interrupts disabled.
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*
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* Return conditions are same as __raw_notifier_call_chain.
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*/
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int cpu_pm_enter(void)
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{
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return cpu_pm_notify_robust(CPU_PM_ENTER, CPU_PM_ENTER_FAILED);
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}
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EXPORT_SYMBOL_GPL(cpu_pm_enter);
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/**
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* cpu_pm_exit - CPU low power exit notifier
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*
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* Notifies listeners that a single CPU is exiting a low power state that may
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* have caused some blocks in the same power domain as the cpu to reset.
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*
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* Notified drivers can include VFP co-processor, interrupt controller
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* and its PM extensions, local CPU timers context save/restore which
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* shouldn't be interrupted. Hence it must be called with interrupts disabled.
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*
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* Return conditions are same as __raw_notifier_call_chain.
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*/
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int cpu_pm_exit(void)
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{
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return cpu_pm_notify(CPU_PM_EXIT);
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}
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EXPORT_SYMBOL_GPL(cpu_pm_exit);
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/**
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* cpu_cluster_pm_enter - CPU cluster low power entry notifier
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*
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* Notifies listeners that all cpus in a power domain are entering a low power
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* state that may cause some blocks in the same power domain to reset.
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*
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* Must be called after cpu_pm_enter has been called on all cpus in the power
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* domain, and before cpu_pm_exit has been called on any cpu in the power
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* domain. Notified drivers can include VFP co-processor, interrupt controller
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* and its PM extensions, local CPU timers context save/restore which
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* shouldn't be interrupted. Hence it must be called with interrupts disabled.
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*
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* Must be called with interrupts disabled.
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*
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* Return conditions are same as __raw_notifier_call_chain.
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*/
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int cpu_cluster_pm_enter(void)
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{
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return cpu_pm_notify_robust(CPU_CLUSTER_PM_ENTER, CPU_CLUSTER_PM_ENTER_FAILED);
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}
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EXPORT_SYMBOL_GPL(cpu_cluster_pm_enter);
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/**
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* cpu_cluster_pm_exit - CPU cluster low power exit notifier
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*
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* Notifies listeners that all cpus in a power domain are exiting form a
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* low power state that may have caused some blocks in the same power domain
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* to reset.
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*
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* Must be called after cpu_cluster_pm_enter has been called for the power
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* domain, and before cpu_pm_exit has been called on any cpu in the power
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* domain. Notified drivers can include VFP co-processor, interrupt controller
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* and its PM extensions, local CPU timers context save/restore which
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* shouldn't be interrupted. Hence it must be called with interrupts disabled.
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*
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* Return conditions are same as __raw_notifier_call_chain.
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*/
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int cpu_cluster_pm_exit(void)
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{
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return cpu_pm_notify(CPU_CLUSTER_PM_EXIT);
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}
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EXPORT_SYMBOL_GPL(cpu_cluster_pm_exit);
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#ifdef CONFIG_PM
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static int cpu_pm_suspend(void)
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{
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int ret;
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ret = cpu_pm_enter();
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if (ret)
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return ret;
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ret = cpu_cluster_pm_enter();
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return ret;
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}
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static void cpu_pm_resume(void)
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{
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cpu_cluster_pm_exit();
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cpu_pm_exit();
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}
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static struct syscore_ops cpu_pm_syscore_ops = {
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.suspend = cpu_pm_suspend,
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.resume = cpu_pm_resume,
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};
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static int cpu_pm_init(void)
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{
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register_syscore_ops(&cpu_pm_syscore_ops);
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return 0;
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}
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core_initcall(cpu_pm_init);
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#endif
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