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PM: cpu: Make notifier chain use a raw_spinlock_t

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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>
This commit is contained in:
Valentin Schneider 2021-08-11 21:14:31 +01:00 committed by Rafael J. Wysocki
parent 7c60610d47
commit b2f6662ac0
1 changed files with 38 additions and 12 deletions
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50
kernel/cpu_pm.c
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@ -13,19 +13,32 @@
#include <linux/spinlock.h>
#include <linux/syscore_ops.h>
static ATOMIC_NOTIFIER_HEAD(cpu_pm_notifier_chain);
/*
* atomic_notifiers use a spinlock_t, which can block under PREEMPT_RT.
* Notifications for cpu_pm will be issued by the idle task itself, which can
* never block, IOW it requires using a raw_spinlock_t.
*/
static struct {
struct raw_notifier_head chain;
raw_spinlock_t lock;
} cpu_pm_notifier = {
.chain = RAW_NOTIFIER_INIT(cpu_pm_notifier.chain),
.lock = __RAW_SPIN_LOCK_UNLOCKED(cpu_pm_notifier.lock),
};
static int cpu_pm_notify(enum cpu_pm_event event)
{
int ret;
/*
* 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.
* This introduces 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);
rcu_read_lock();
ret = raw_notifier_call_chain(&cpu_pm_notifier.chain, event, NULL);
rcu_read_unlock();
rcu_irq_exit_irqson();
return notifier_to_errno(ret);
@ -33,10 +46,13 @@ static int cpu_pm_notify(enum cpu_pm_event event)
static int cpu_pm_notify_robust(enum cpu_pm_event event_up, enum cpu_pm_event event_down)
{
unsigned long flags;
int ret;
rcu_irq_enter_irqson();
ret = atomic_notifier_call_chain_robust(&cpu_pm_notifier_chain, event_up, event_down, NULL);
raw_spin_lock_irqsave(&cpu_pm_notifier.lock, flags);
ret = raw_notifier_call_chain_robust(&cpu_pm_notifier.chain, event_up, event_down, NULL);
raw_spin_unlock_irqrestore(&cpu_pm_notifier.lock, flags);
rcu_irq_exit_irqson();
return notifier_to_errno(ret);
@ -49,12 +65,17 @@ static int cpu_pm_notify_robust(enum cpu_pm_event event_up, enum cpu_pm_event ev
* Add a driver to a list of drivers that are notified about
* CPU and CPU cluster low power entry and exit.
*
* This function may sleep, and has the same return conditions as
* raw_notifier_chain_register.
* This function has the same return conditions as raw_notifier_chain_register.
*/
int cpu_pm_register_notifier(struct notifier_block *nb)
{
return atomic_notifier_chain_register(&cpu_pm_notifier_chain, nb);
unsigned long flags;
int ret;
raw_spin_lock_irqsave(&cpu_pm_notifier.lock, flags);
ret = raw_notifier_chain_register(&cpu_pm_notifier.chain, nb);
raw_spin_unlock_irqrestore(&cpu_pm_notifier.lock, flags);
return ret;
}
EXPORT_SYMBOL_GPL(cpu_pm_register_notifier);
@ -64,12 +85,17 @@ EXPORT_SYMBOL_GPL(cpu_pm_register_notifier);
*
* Remove a driver from the CPU PM notifier list.
*
* This function may sleep, and has the same return conditions as
* raw_notifier_chain_unregister.
* This function has the same return conditions as raw_notifier_chain_unregister.
*/
int cpu_pm_unregister_notifier(struct notifier_block *nb)
{
return atomic_notifier_chain_unregister(&cpu_pm_notifier_chain, nb);
unsigned long flags;
int ret;
raw_spin_lock_irqsave(&cpu_pm_notifier.lock, flags);
ret = raw_notifier_chain_unregister(&cpu_pm_notifier.chain, nb);
raw_spin_unlock_irqrestore(&cpu_pm_notifier.lock, flags);
return ret;
}
EXPORT_SYMBOL_GPL(cpu_pm_unregister_notifier);