linux-kernel - Re: [PATCH] sched, cpuidle: Do not access cpuidle_devices when !CONFIG_CPU

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Date:	Wed, 01 Jun 2016 22:20:03 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrey Ryabinin <aryabinin@...tuozzo.com>
Subject: Re: [PATCH] sched, cpuidle: Do not access cpuidle_devices when !CONFIG_CPU_IDLE

On Wednesday, June 01, 2016 06:52:16 PM Catalin Marinas wrote:
> The cpuidle_devices per-CPU variable is only defined when CPU_IDLE is
> enabled. Commit c8cc7d4de7a4 ("sched/idle: Reorganize the idle loop")
> removed the #ifdef CONFIG_CPU_IDLE around cpuidle_idle_call() with the
> compiler optimising away __this_cpu_read(cpuidle_devices). However, with
> CONFIG_UBSAN && !CONFIG_CPU_IDLE, this optimisation no longer happens
> and the kernel fails to link since cpuidle_devices is not defined.
> 
> This patch introduces an accessor function for the current CPU cpuidle
> device (returning NULL when !CONFIG_CPU_IDLE) and uses it in
> cpuidle_idle_call().
> 
> Cc: Rafael J. Wysocki <rjw@...ysocki.net>
> Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Andrey Ryabinin <aryabinin@...tuozzo.com>
> Signed-off-by: Catalin Marinas <catalin.marinas@....com>

OK

Is this needed in -stable?

> ---
> 
> This fixes a build failure on arm64 with UBSAN && !CPU_IDLE and gcc
> 5.3.1 (probably other compiler versions would behave in the same way).
> 
> I tried to keep close to the existing coding style in cpuidle.h.
> 
>  include/linux/cpuidle.h | 3 +++
>  kernel/sched/idle.c     | 2 +-
>  2 files changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
> index 786ad32631a6..07b83d32f66c 100644
> --- a/include/linux/cpuidle.h
> +++ b/include/linux/cpuidle.h
> @@ -152,6 +152,8 @@ extern void cpuidle_disable_device(struct cpuidle_device *dev);
>  extern int cpuidle_play_dead(void);
>  
>  extern struct cpuidle_driver *cpuidle_get_cpu_driver(struct cpuidle_device *dev);
> +static inline struct cpuidle_device *cpuidle_get_device(void)
> +{return __this_cpu_read(cpuidle_devices); }
>  #else
>  static inline void disable_cpuidle(void) { }
>  static inline bool cpuidle_not_available(struct cpuidle_driver *drv,
> @@ -187,6 +189,7 @@ static inline void cpuidle_disable_device(struct cpuidle_device *dev) { }
>  static inline int cpuidle_play_dead(void) {return -ENODEV; }
>  static inline struct cpuidle_driver *cpuidle_get_cpu_driver(
>  	struct cpuidle_device *dev) {return NULL; }
> +static inline struct cpuidle_device *cpuidle_get_device(void) {return NULL; }
>  #endif
>  
>  #if defined(CONFIG_CPU_IDLE) && defined(CONFIG_SUSPEND)
> diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
> index bd12c6c714ec..c5aeedf4e93a 100644
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -127,7 +127,7 @@ static int call_cpuidle(struct cpuidle_driver *drv, struct cpuidle_device *dev,
>   */
>  static void cpuidle_idle_call(void)
>  {
> -	struct cpuidle_device *dev = __this_cpu_read(cpuidle_devices);
> +	struct cpuidle_device *dev = cpuidle_get_device();
>  	struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
>  	int next_state, entered_state;
>