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 Lindgren 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 <[email protected]>
Tested-by: Tony Lindgren <[email protected]>
To: [email protected]
Cc: Sebastian Andrzej Siewior <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Anders Roxell <[email protected]>
Cc: Daniel Lezcano <[email protected]>
Cc: Rafael J. Wysocki <[email protected]>
Cc: Tony Lindgren <[email protected]>
Cc: [email protected]
Cc: linux-rt-users <[email protected]>
Acked-by: Sebastian Andrzej Siewior <[email protected]>
---
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 009cc9a..67b02e1 100644
--- a/kernel/cpu_pm.c
+++ b/kernel/cpu_pm.c
@@ -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);
--
2.7.4
On Friday, July 28, 2017 03:09:25 PM 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.
>
> Tony Lindgren 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 <[email protected]>
> Tested-by: Tony Lindgren <[email protected]>
> To: [email protected]
> Cc: Sebastian Andrzej Siewior <[email protected]>
> Cc: Thomas Gleixner <[email protected]>
> Cc: Anders Roxell <[email protected]>
> Cc: Daniel Lezcano <[email protected]>
> Cc: Rafael J. Wysocki <[email protected]>
> Cc: Tony Lindgren <[email protected]>
> Cc: [email protected]
> Cc: linux-rt-users <[email protected]>
> Acked-by: Sebastian Andrzej Siewior <[email protected]>
Applied, thanks!