linux-kernel - Re: [PATCH v3 35/51] trace,hardirq: No moar

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Message-Id: <20230117132446.02ec12e4c10718de27790900@kernel.org>
Date:   Tue, 17 Jan 2023 13:24:46 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
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Subject: Re: [PATCH v3 35/51] trace,hardirq: No moar _rcuidle() tracing

Hi Peter,

On Thu, 12 Jan 2023 20:43:49 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> Robot reported that trace_hardirqs_{on,off}() tickle the forbidden
> _rcuidle() tracepoint through local_irq_{en,dis}able().
> 
> For 'sane' configs, these calls will only happen with RCU enabled and
> as such can use the regular tracepoint. This also means it's possible
> to trace them from NMI context again.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

The code looks good to me. I just have a question about comment.

> ---
>  kernel/trace/trace_preemptirq.c |   21 +++++++++++++--------
>  1 file changed, 13 insertions(+), 8 deletions(-)
> 
> --- a/kernel/trace/trace_preemptirq.c
> +++ b/kernel/trace/trace_preemptirq.c
> @@ -20,6 +20,15 @@
>  static DEFINE_PER_CPU(int, tracing_irq_cpu);
>  
>  /*
> + * ...

Is this intended? Wouldn't you leave any comment here?

Thank you,

> + */
> +#ifdef CONFIG_ARCH_WANTS_NO_INSTR
> +#define trace(point)	trace_##point
> +#else
> +#define trace(point)	if (!in_nmi()) trace_##point##_rcuidle
> +#endif
> +
> +/*
>   * Like trace_hardirqs_on() but without the lockdep invocation. This is
>   * used in the low level entry code where the ordering vs. RCU is important
>   * and lockdep uses a staged approach which splits the lockdep hardirq
> @@ -28,8 +37,7 @@ static DEFINE_PER_CPU(int, tracing_irq_c
>  void trace_hardirqs_on_prepare(void)
>  {
>  	if (this_cpu_read(tracing_irq_cpu)) {
> -		if (!in_nmi())
> -			trace_irq_enable(CALLER_ADDR0, CALLER_ADDR1);
> +		trace(irq_enable)(CALLER_ADDR0, CALLER_ADDR1);
>  		tracer_hardirqs_on(CALLER_ADDR0, CALLER_ADDR1);
>  		this_cpu_write(tracing_irq_cpu, 0);
>  	}
> @@ -40,8 +48,7 @@ NOKPROBE_SYMBOL(trace_hardirqs_on_prepar
>  void trace_hardirqs_on(void)
>  {
>  	if (this_cpu_read(tracing_irq_cpu)) {
> -		if (!in_nmi())
> -			trace_irq_enable_rcuidle(CALLER_ADDR0, CALLER_ADDR1);
> +		trace(irq_enable)(CALLER_ADDR0, CALLER_ADDR1);
>  		tracer_hardirqs_on(CALLER_ADDR0, CALLER_ADDR1);
>  		this_cpu_write(tracing_irq_cpu, 0);
>  	}
> @@ -63,8 +70,7 @@ void trace_hardirqs_off_finish(void)
>  	if (!this_cpu_read(tracing_irq_cpu)) {
>  		this_cpu_write(tracing_irq_cpu, 1);
>  		tracer_hardirqs_off(CALLER_ADDR0, CALLER_ADDR1);
> -		if (!in_nmi())
> -			trace_irq_disable(CALLER_ADDR0, CALLER_ADDR1);
> +		trace(irq_disable)(CALLER_ADDR0, CALLER_ADDR1);
>  	}
>  
>  }
> @@ -78,8 +84,7 @@ void trace_hardirqs_off(void)
>  	if (!this_cpu_read(tracing_irq_cpu)) {
>  		this_cpu_write(tracing_irq_cpu, 1);
>  		tracer_hardirqs_off(CALLER_ADDR0, CALLER_ADDR1);
> -		if (!in_nmi())
> -			trace_irq_disable_rcuidle(CALLER_ADDR0, CALLER_ADDR1);
> +		trace(irq_disable)(CALLER_ADDR0, CALLER_ADDR1);
>  	}
>  }
>  EXPORT_SYMBOL(trace_hardirqs_off);
> 
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>