From 313c8c16ee62b32b8b40c6b00637b401dc19050e Mon Sep 17 00:00:00 2001 From: Alex Shi Date: Fri, 28 Jul 2017 15:09:25 +0800 Subject: [PATCH] PM / CPU: replace raw_notifier with atomic_notifier 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] [] arm_enter_idle_state+0x18/0x70 [ 4.609614] Modules linked in: [ 4.609615] [] cpuidle_enter_state+0xf0/0x218 [ 4.609620] [] cpuidle_enter+0x18/0x20 [ 4.609626] Preemption disabled at: [ 4.609627] [] call_cpuidle+0x24/0x40 [ 4.609635] [] schedule_preempt_disabled+0x1c/0x28 [ 4.609639] [] cpu_startup_entry+0x154/0x1f8 [ 4.609645] [] 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 Tested-by: Tony Lindgren Acked-by: Sebastian Andrzej Siewior [ rjw: Subject & changelog ] Signed-off-by: Rafael J. Wysocki --- kernel/cpu_pm.c | 50 +++++++++++++------------------------------------ 1 file changed, 13 insertions(+), 37 deletions(-) diff --git a/kernel/cpu_pm.c b/kernel/cpu_pm.c index 009cc9a17d95..67b02e138a47 100644 --- a/kernel/cpu_pm.c +++ b/kernel/cpu_pm.c @@ -22,15 +22,21 @@ #include #include -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);