This is a quick fix for a bug as 'scheduling while atomic' or
'scheduling from the idle thread' on arm/arm64.
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.
I also tried use local_lock_irq to replace local_irq_disable, but my 2
boards just die without any output. So maybe it's only quick way to
make rt kernel work on arm/arm64.
Since this is quick fix, instead of split out the raw rwlock, to use
raw_spin_lock is simple and don't cost much.
Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxx>
Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Anders Roxell <anders.roxell@xxxxxxxxxx>
Cc: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
Cc: linux-rt-users <linux-rt-users@xxxxxxxxxxxxxxx>
---
kernel/cpu_pm.c | 26 +++++++++++++-------------
1 file changed, 13 insertions(+), 13 deletions(-)
diff --git a/kernel/cpu_pm.c b/kernel/cpu_pm.c
index 009cc9a..8ffa13e3 100644
--- a/kernel/cpu_pm.c
+++ b/kernel/cpu_pm.c
@@ -22,7 +22,7 @@
#include <linux/spinlock.h>
#include <linux/syscore_ops.h>
-static DEFINE_RWLOCK(cpu_pm_notifier_lock);
+static DEFINE_RAW_SPINLOCK(cpu_pm_notifier_lock);
static RAW_NOTIFIER_HEAD(cpu_pm_notifier_chain);
static int cpu_pm_notify(enum cpu_pm_event event, int nr_to_call, int *nr_calls)
@@ -50,9 +50,9 @@ int cpu_pm_register_notifier(struct notifier_block *nb)
unsigned long flags;
int ret;
- write_lock_irqsave(&cpu_pm_notifier_lock, flags);
+ raw_spin_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);
+ raw_spin_unlock_irqrestore(&cpu_pm_notifier_lock, flags);
return ret;
}
@@ -72,9 +72,9 @@ int cpu_pm_unregister_notifier(struct notifier_block *nb)
unsigned long flags;
int ret;
- write_lock_irqsave(&cpu_pm_notifier_lock, flags);
+ raw_spin_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);
+ raw_spin_unlock_irqrestore(&cpu_pm_notifier_lock, flags);
return ret;
}
@@ -100,7 +100,7 @@ int cpu_pm_enter(void)
int nr_calls;
int ret = 0;
- read_lock(&cpu_pm_notifier_lock);
+ raw_spin_lock(&cpu_pm_notifier_lock);
ret = cpu_pm_notify(CPU_PM_ENTER, -1, &nr_calls);
if (ret)
/*
@@ -108,7 +108,7 @@ 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);
+ raw_spin_unlock(&cpu_pm_notifier_lock);
return ret;
}
@@ -130,9 +130,9 @@ int cpu_pm_exit(void)
{
int ret;
- read_lock(&cpu_pm_notifier_lock);
+ raw_spin_lock(&cpu_pm_notifier_lock);
ret = cpu_pm_notify(CPU_PM_EXIT, -1, NULL);
- read_unlock(&cpu_pm_notifier_lock);
+ raw_spin_unlock(&cpu_pm_notifier_lock);
return ret;
}
@@ -159,7 +159,7 @@ int cpu_cluster_pm_enter(void)
int nr_calls;
int ret = 0;
- read_lock(&cpu_pm_notifier_lock);
+ raw_spin_lock(&cpu_pm_notifier_lock);
ret = cpu_pm_notify(CPU_CLUSTER_PM_ENTER, -1, &nr_calls);
if (ret)
/*
@@ -167,7 +167,7 @@ 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);
+ raw_spin_unlock(&cpu_pm_notifier_lock);
return ret;
}
@@ -192,9 +192,9 @@ int cpu_cluster_pm_exit(void)
{
int ret;
- read_lock(&cpu_pm_notifier_lock);
+ raw_spin_lock(&cpu_pm_notifier_lock);
ret = cpu_pm_notify(CPU_CLUSTER_PM_EXIT, -1, NULL);
- read_unlock(&cpu_pm_notifier_lock);
+ raw_spin_unlock(&cpu_pm_notifier_lock);
return ret;
}
--
1.9.1
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