| Message ID | 1499820498-7983-1-git-send-email-alex.shi@linaro.org (mailing list archive) |
|---|---|
| State | Mainlined |
| Delegated to: | Rafael Wysocki |
| Headers | show |
On Wednesday, July 12, 2017 08:48:18 AM Alex Shi wrote: > 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. > > This patch passed Fengguang's 0day testing. > > Signed-off-by: Alex Shi <alex.shi@linaro.org> > 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: linux-rt-users <linux-rt-users@vger.kernel.org> > Cc: linux-pm@vger.kernel.org > Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Applied (although you have forgotten to CC me actually). Thanks, Rafael
On 07/13/2017 05:30 AM, Rafael J. Wysocki wrote: >> >> This patch passed Fengguang's 0day testing. >> >> Signed-off-by: Alex Shi <alex.shi@linaro.org> >> 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: linux-rt-users <linux-rt-users@vger.kernel.org> >> Cc: linux-pm@vger.kernel.org >> Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> > Applied (although you have forgotten to CC me actually). Ops, My bad. I shouldn't resend email just few minutes before bed time. :( I will take this lesson. Regards Alex
diff --git a/kernel/cpu_pm.c b/kernel/cpu_pm.c index 009cc9a..10f4640 100644 --- a/kernel/cpu_pm.c +++ b/kernel/cpu_pm.c @@ -22,14 +22,13 @@ #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, + 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; - - 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 +61,7 @@ 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 +85,6 @@ 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 +92,6 @@ 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 +111,7 @@ 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 +136,6 @@ 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 +143,6 @@ 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 +165,7 @@ 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. This patch passed Fengguang's 0day testing. Signed-off-by: Alex Shi <alex.shi@linaro.org> 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: linux-rt-users <linux-rt-users@vger.kernel.org> Cc: linux-pm@vger.kernel.org Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- kernel/cpu_pm.c | 43 ++++++------------------------------------- 1 file changed, 6 insertions(+), 37 deletions(-)