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@xxxxxxxxxx> > To: linux-kernel@xxxxxxxxxxxxxxx > 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> > Cc: linux-pm@xxxxxxxxxxxxxxx > Acked-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Applied (although you have forgotten to CC me actually). Thanks, Rafael -- 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
