linux-kernel - Re: [PATCH] preempt: add in_serving_irq() and apply to rcutiny and vsprintf

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Date:   Tue, 17 Aug 2021 00:03:16 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     Changbin Du <changbin.du@...il.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        linux-kernel@...r.kernel.org, rcu@...r.kernel.org
Subject: Re: [PATCH] preempt: add in_serving_irq() and apply to rcutiny and
 vsprintf

On Sat, Aug 14, 2021 at 09:42:34AM +0800, Changbin Du wrote:
> At some places we need to determine whether we're in nmi, hardirq or
> softirq context. This adds a macro in_serving_irq() as a shortcut for
> that.
> 
> Meanwhile, apply this new macro to existing code in rcutiny and vsprintf.
> 
> Signed-off-by: Changbin Du <changbin.du@...il.com>
> ---
>  include/linux/preempt.h | 4 +++-
>  include/linux/rcutiny.h | 3 +--
>  lib/vsprintf.c          | 2 +-
>  3 files changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/preempt.h b/include/linux/preempt.h
> index 9881eac0698f..9a1c924e2c6c 100644
> --- a/include/linux/preempt.h
> +++ b/include/linux/preempt.h
> @@ -92,12 +92,14 @@
>   * in_nmi()		- We're in NMI context
>   * in_hardirq()		- We're in hard IRQ context
>   * in_serving_softirq()	- We're in softirq context
> + * in_serving_irq()	- We're in nmi, hardirq or softirq context
>   * in_task()		- We're in task context
>   */
>  #define in_nmi()		(nmi_count())
>  #define in_hardirq()		(hardirq_count())
>  #define in_serving_softirq()	(softirq_count() & SOFTIRQ_OFFSET)
> -#define in_task()		(!(in_nmi() | in_hardirq() | in_serving_softirq()))
> +#define in_serving_irq()	(in_nmi() | in_hardirq() | in_serving_softirq())
> +#define in_task()		(!in_serving_irq())
>  

So in_serving_irq() is !in_task(), right? If so, why not...

>  /*
>   * The following macros are deprecated and should not be used in new code:
> diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
> index 7fedbd33d5d2..812d42f22e9c 100644
> --- a/include/linux/rcutiny.h
> +++ b/include/linux/rcutiny.h
> @@ -87,8 +87,7 @@ static inline void rcu_irq_exit_irqson(void) { }
>  static inline void rcu_irq_enter_irqson(void) { }
>  static inline void rcu_irq_exit(void) { }
>  static inline void rcu_irq_exit_check_preempt(void) { }
> -#define rcu_is_idle_cpu(cpu) \
> -	(is_idle_task(current) && !in_nmi() && !in_hardirq() && !in_serving_softirq())
> +#define rcu_is_idle_cpu(cpu) (is_idle_task(current) && !in_serving_irq())

... use in_task() here, and ...

>  static inline void exit_rcu(void) { }
>  static inline bool rcu_preempt_need_deferred_qs(struct task_struct *t)
>  {
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 2c5b4351330c..9324439c8543 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -865,7 +865,7 @@ char *restricted_pointer(char *buf, char *end, const void *ptr,
>  		 * kptr_restrict==1 cannot be used in IRQ context
>  		 * because its test for CAP_SYSLOG would be meaningless.
>  		 */
> -		if (in_hardirq() || in_serving_softirq() || in_nmi()) {
> +		if (in_serving_irq()) {

... use !in_task() here?

And don't introduce the in_serving_irq() at all.

Regards,
Boqun

>  			if (spec.field_width == -1)
>  				spec.field_width = 2 * sizeof(ptr);
>  			return error_string(buf, end, "pK-error", spec);
> -- 
> 2.30.2
>