On 2017-06-14 21:22:19 [+0800], Alex Shi wrote: > 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. I must have it disabled on my juno64 (and my 32bit boxes) since I haven't seen it. So we end up in IRQ off section and can't do anything about it. So DEFINE_RAW_SPINLOCK it is? Can we have this upstream, please? Or is that reader/writer part *so* important? If so would it work to move that part to atomic_notifier_*() and have rcu_read_lock() instead that read_lock()? Sebastian -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
