Re: [PATCH v2] tracing: Remove definition of trace_*_rcuidle()

[Madhavan Srinivasan <maddy@linux.ibm.com>]

On 12/4/24 8:31 AM, Steven Rostedt wrote:
> On Tue, 3 Dec 2024 17:48:33 -0800
> Guenter Roeck <linux@roeck-us.net> wrote:
> 
>> Hmm. If you say so. Note that powerpc has the same or a similar problem.
>>
>> [    0.142039][    T0] RCU not watching for tracepoint
>> [    0.142488][    T0]
>> [    0.142659][    T0] =============================
>> [    0.142755][    T0] WARNING: suspicious RCU usage
>> [    0.142914][    T0] 6.13.0-rc1-00058-ge75ce84aa5d3 #1 Not tainted
>> [    0.143082][    T0] -----------------------------
>> [    0.143178][    T0] kernel/notifier.c:586 notify_die called but RCU thinks we're quiescent!
>>
>>
>> [    0.152733][    T0] RCU not watching for tracepoint
>> [    0.152770][    T0]
>> [    0.152995][    T0] =============================
>> [    0.153092][    T0] WARNING: suspicious RCU usage
>> [    0.153187][    T0] 6.13.0-rc1-00058-ge75ce84aa5d3 #1 Not tainted
>> [    0.153301][    T0] -----------------------------
>> [    0.153394][    T0] include/linux/rcupdate.h:850 rcu_read_lock() used illegally while idle!
>>
>> [    0.165396][    T0] RCU not watching for tracepoint
>> [    0.165540][    T0]
>> [    0.165712][    T0] =============================
>> [    0.165811][    T0] WARNING: suspicious RCU usage
>> [    0.165909][    T0] 6.13.0-rc1-00058-ge75ce84aa5d3 #1 Not tainted
>> [    0.166026][    T0] -----------------------------
>> [    0.166122][    T0] include/linux/rcupdate.h:878 rcu_read_unlock() used illegally while idle!
>>
>> and many more.
> 
> Grumble. It's just that one file. I wonder if we could just do a hack like
> this?
> 

Below patch fixes the issue in powerpc
Tested-by: Madhavan Srinivasan <maddy@linux.ibm.com>

Thanks
maddy

> Paul?
> 
> diff --git a/kernel/trace/trace_preemptirq.c b/kernel/trace/trace_preemptirq.c
> index 5c03633316a6..58098873efa9 100644
> --- a/kernel/trace/trace_preemptirq.c
> +++ b/kernel/trace/trace_preemptirq.c
> @@ -10,11 +10,42 @@
>  #include <linux/module.h>
>  #include <linux/ftrace.h>
>  #include <linux/kprobes.h>
> +#include <linux/hardirq.h>
>  #include "trace.h"
>  
>  #define CREATE_TRACE_POINTS
>  #include <trace/events/preemptirq.h>
>  
> +/*
> + * Use regular trace points on architectures that implement noinstr
> + * tooling: these calls will only happen with RCU enabled, which can
> + * use a regular tracepoint.
> + *
> + * On older architectures, RCU may not be watching in idle. In that
> + * case, wake up RCU to watch while calling the tracepoint. These
> + * aren't NMI-safe - so exclude NMI contexts:
> + */
> +#ifdef CONFIG_ARCH_WANTS_NO_INSTR
> +#define trace(point, args)	trace_##point(args)
> +#else
> +#define trace(point, args)					\
> +	do {							\
> +		if (trace_##point##_enabled()) {		\
> +			bool exit_rcu = false;			\
> +			if (in_nmi())				\
> +				break;				\
> +			if (!IS_ENABLED(CONFIG_TINY_RCU) &&	\
> +			    is_idle_task(current)) {		\
> +				ct_irq_enter();			\
> +				exit_rcu = true;		\
> +			}					\
> +			trace_##point(args);			\
> +			if (exit_rcu)				\
> +				ct_irq_exit();			\
> +		}						\
> +	} while (0)
> +#endif
> +
>  #ifdef CONFIG_TRACE_IRQFLAGS
>  /* Per-cpu variable to prevent redundant calls when IRQs already off */
>  static DEFINE_PER_CPU(int, tracing_irq_cpu);
> @@ -28,7 +59,7 @@ static DEFINE_PER_CPU(int, tracing_irq_cpu);
>  void trace_hardirqs_on_prepare(void)
>  {
>  	if (this_cpu_read(tracing_irq_cpu)) {
> -		trace_irq_enable(CALLER_ADDR0, CALLER_ADDR1);
> +		trace(irq_enable, TP_ARGS(CALLER_ADDR0, CALLER_ADDR1));
>  		tracer_hardirqs_on(CALLER_ADDR0, CALLER_ADDR1);
>  		this_cpu_write(tracing_irq_cpu, 0);
>  	}
> @@ -39,7 +70,7 @@ NOKPROBE_SYMBOL(trace_hardirqs_on_prepare);
>  void trace_hardirqs_on(void)
>  {
>  	if (this_cpu_read(tracing_irq_cpu)) {
> -		trace_irq_enable(CALLER_ADDR0, CALLER_ADDR1);
> +		trace(irq_enable, TP_ARGS(CALLER_ADDR0, CALLER_ADDR1));
>  		tracer_hardirqs_on(CALLER_ADDR0, CALLER_ADDR1);
>  		this_cpu_write(tracing_irq_cpu, 0);
>  	}
> @@ -61,7 +92,7 @@ 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);
> -		trace_irq_disable(CALLER_ADDR0, CALLER_ADDR1);
> +		trace(irq_disable, TP_ARGS(CALLER_ADDR0, CALLER_ADDR1));
>  	}
>  
>  }
> @@ -75,7 +106,7 @@ 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);
> -		trace_irq_disable(CALLER_ADDR0, CALLER_ADDR1);
> +		trace(irq_disable, TP_ARGS(CALLER_ADDR0, CALLER_ADDR1));
>  	}
>  }
>  EXPORT_SYMBOL(trace_hardirqs_off);
> @@ -86,13 +117,13 @@ NOKPROBE_SYMBOL(trace_hardirqs_off);
>  
>  void trace_preempt_on(unsigned long a0, unsigned long a1)
>  {
> -	trace_preempt_enable(a0, a1);
> +	trace(preempt_enable, TP_ARGS(a0, a1));
>  	tracer_preempt_on(a0, a1);
>  }
>  
>  void trace_preempt_off(unsigned long a0, unsigned long a1)
>  {
> -	trace_preempt_disable(a0, a1);
> +	trace(preempt_disable, TP_ARGS(a0, a1));
>  	tracer_preempt_off(a0, a1);
>  }
>  #endif
> 
> 
> I tested this by forcing x86 to use this code, and it appeared to work.
> 
> -- Steve
> 
>