@@ -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);
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] [<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 getting better latency improvement. Tony Lezcano found a miss use that rcu_read_lock used after rcu_idle_enter Paul E. McKenney suggested trying RCU_NONIDLE. Thanks everyone! :) This patch passed Fengguang's 0day testing. Signed-off-by: Alex Shi <alex.shi@linaro.org> Tested-by: Tony Lindgren <tony@atomide.com> To: linux-kernel@vger.kernel.org Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Anders Roxell <anders.roxell@linaro.org> Cc: Daniel Lezcano <daniel.lezcano@linaro.org> Cc: Rafael J. Wysocki <rafael@kernel.org> Cc: Tony Lindgren <tony@atomide.com> Cc: linux-pm@vger.kernel.org Cc: linux-rt-users <linux-rt-users@vger.kernel.org> Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- kernel/cpu_pm.c | 50 +++++++++++++------------------------------------- 1 file changed, 13 insertions(+), 37 deletions(-)