1. 31 Jul, 2017 1 commit
    • Alex Shi's avatar
      PM / CPU: replace raw_notifier with atomic_notifier · 313c8c16
      Alex Shi authored
      This patch replaces an rwlock and raw notifier by an atomic notifier
      protected by a spin_lock and RCU.
      
      The main reason for this change is due to a 'scheduling while atomic'
      bug with RT kernels on ARM/ARM64. On ARM/ARM64, the rwlock
      cpu_pm_notifier_lock in cpu_pm_enter/exit() causes a potential
      schedule after IRQ disable in the 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 improving latency.
      
      Tony Lindgren found a miss use that rcu_read_lock used after rcu_idle_enter
      Paul McKenney suggested trying RCU_NONIDLE.
      Signed-off-by: default avatarAlex Shi <alex.shi@linaro.org>
      Tested-by: default avatarTony Lindgren <tony@atomide.com>
      Acked-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
      [ rjw: Subject & changelog ]
      Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
      313c8c16
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