From 5b084b5f2db83094cb7e278b8b0e60f22a8539a4 Mon Sep 17 00:00:00 2001 From: Alex Shi Date: Thu, 6 Jul 2017 16:47:46 +0800 Subject: [PATCH 332/365] cpu_pm: replace raw_notifier to atomic_notifier 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] [] 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 getting better latency improvement. This patch passed Fengguang's 0day testing. Change-Id: I2904a22ddca1ede7d7aea1430db9c4d0c1a7a34d Signed-off-by: Alex Shi Cc: Sebastian Andrzej Siewior Cc: Thomas Gleixner Cc: Anders Roxell Cc: Rik van Riel Cc: Steven Rostedt Cc: Rafael J. Wysocki Cc: Daniel Lezcano Cc: linux-rt-users Signed-off-by: Sebastian Andrzej Siewior --- kernel/cpu_pm.c | 45 ++++++--------------------------------------- 1 file changed, 6 insertions(+), 39 deletions(-) diff --git a/kernel/cpu_pm.c b/kernel/cpu_pm.c index c431b5cdbc23..f6a81195f775 100644 --- a/kernel/cpu_pm.c +++ b/kernel/cpu_pm.c @@ -22,14 +22,13 @@ #include #include -static DEFINE_RAW_SPINLOCK(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, + ret = __atomic_notifier_call_chain(&cpu_pm_notifier_chain, event, NULL, nr_to_call, nr_calls); return notifier_to_errno(ret); @@ -47,14 +46,7 @@ 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; - - 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; + return atomic_notifier_chain_register(&cpu_pm_notifier_chain, nb); } EXPORT_SYMBOL_GPL(cpu_pm_register_notifier); @@ -69,14 +61,7 @@ EXPORT_SYMBOL_GPL(cpu_pm_register_notifier); */ int cpu_pm_unregister_notifier(struct notifier_block *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; + return atomic_notifier_chain_unregister(&cpu_pm_notifier_chain, nb); } EXPORT_SYMBOL_GPL(cpu_pm_unregister_notifier); @@ -101,7 +86,6 @@ int cpu_pm_enter(void) int ret = 0; unsigned long flags; - raw_spin_lock_irqsave(&cpu_pm_notifier_lock, flags); ret = cpu_pm_notify(CPU_PM_ENTER, -1, &nr_calls); if (ret) /* @@ -109,7 +93,6 @@ 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); - raw_spin_unlock_irqrestore(&cpu_pm_notifier_lock, flags); return ret; } @@ -129,14 +112,7 @@ EXPORT_SYMBOL_GPL(cpu_pm_enter); */ int cpu_pm_exit(void) { - int ret; - unsigned long flags; - - raw_spin_lock_irqsave(&cpu_pm_notifier_lock, flags); - ret = cpu_pm_notify(CPU_PM_EXIT, -1, NULL); - raw_spin_unlock_irqrestore(&cpu_pm_notifier_lock, flags); - - return ret; + return cpu_pm_notify(CPU_PM_EXIT, -1, NULL); } EXPORT_SYMBOL_GPL(cpu_pm_exit); @@ -162,7 +138,6 @@ int cpu_cluster_pm_enter(void) int ret = 0; unsigned long flags; - raw_spin_lock_irqsave(&cpu_pm_notifier_lock, flags); ret = cpu_pm_notify(CPU_CLUSTER_PM_ENTER, -1, &nr_calls); if (ret) /* @@ -170,7 +145,6 @@ 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); - raw_spin_unlock_irqrestore(&cpu_pm_notifier_lock, flags); return ret; } @@ -193,14 +167,7 @@ EXPORT_SYMBOL_GPL(cpu_cluster_pm_enter); */ int cpu_cluster_pm_exit(void) { - int ret; - unsigned long flags; - - raw_spin_lock_irqsave(&cpu_pm_notifier_lock, flags); - ret = cpu_pm_notify(CPU_CLUSTER_PM_EXIT, -1, NULL); - raw_spin_unlock_irqrestore(&cpu_pm_notifier_lock, flags); - - return ret; + return cpu_pm_notify(CPU_CLUSTER_PM_EXIT, -1, NULL); } EXPORT_SYMBOL_GPL(cpu_cluster_pm_exit); -- 2.28.0