[RFC patch powerpc,trace] Avoid suspicious RCU usage reporting for some tracepoints

[Benjamin Herrenschmidt]

On Mon, 2012-09-10 at 12:58 +0800, Li Zhong wrote:
> There are a few tracepoints in the interrupt code path, which is before
> irq_enter(), or after irq_exit(), like
> trace_irq_entry()/trace_irq_exit() in do_IRQ(),
> trace_timer_interrupt_entry()/trace_timer_interrupt_exit() in
> timer_interrupt(). 
> 
> If the interrupt is from idle(), and because tracepoint contains RCU
> read-side critical section, we could see following suspicious RCU usage
> reported:

 .../...

> This is because the RCU usage in interrupt context should be used in
> area marked by rcu_irq_enter()/rcu_irq_exit(), called in
> irq_enter()/irq_exit() respectively. 
> 
> Could we add a new tracepoint trace_***_rcuirq, like trace_***_rcuidle
> to avoid the report? like the code attached below.
> 
> Or could we just move these tracepoints inside the
> irq_enter()/irq_exit() area? (Seems not good for the timer_interrupt
> case). 

I'd say just move them in. Anton, any objection ?

> Thanks, Zhong
> 
> Signed-off-by: Li Zhong <zhong at linux.vnet.ibm.com>
> ---
>  arch/powerpc/kernel/irq.c  |    4 ++--
>  arch/powerpc/kernel/time.c |    4 ++--
>  include/linux/tracepoint.h |   10 ++++++++++
>  3 files changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
> index 1f017bb..f0ac4e7 100644
> --- a/arch/powerpc/kernel/irq.c
> +++ b/arch/powerpc/kernel/irq.c
> @@ -489,7 +489,7 @@ void do_IRQ(struct pt_regs *regs)
>  	struct pt_regs *old_regs = set_irq_regs(regs);
>  	unsigned int irq;
>  
> -	trace_irq_entry(regs);
> +	trace_irq_entry_rcuirq(regs);
>  
>  	irq_enter();
>  
> @@ -514,7 +514,7 @@ void do_IRQ(struct pt_regs *regs)
>  	irq_exit();
>  	set_irq_regs(old_regs);
>  
> -	trace_irq_exit(regs);
> +	trace_irq_exit_rcuirq(regs);
>  }
>  
>  void __init init_IRQ(void)
> diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
> index e49e931..cbd6607 100644
> --- a/arch/powerpc/kernel/time.c
> +++ b/arch/powerpc/kernel/time.c
> @@ -493,7 +493,7 @@ void timer_interrupt(struct pt_regs * regs)
>  	 */
>  	may_hard_irq_enable();
>  
> -	trace_timer_interrupt_entry(regs);
> +	trace_timer_interrupt_entry_rcuirq(regs);
>  
>  	__get_cpu_var(irq_stat).timer_irqs++;
>  
> @@ -532,7 +532,7 @@ void timer_interrupt(struct pt_regs * regs)
>  	irq_exit();
>  	set_irq_regs(old_regs);
>  
> -	trace_timer_interrupt_exit(regs);
> +	trace_timer_interrupt_exit_rcuirq(regs);
>  }
>  
>  /*
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index 802de56..f7672d5 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -161,6 +161,16 @@ static inline void tracepoint_synchronize_unregister(void)
>  				rcu_idle_exit(),			\
>  				rcu_idle_enter());			\
>  	}								\
> +	static inline void trace_##name##_rcuirq(proto)			\
> +	{								\
> +		if (static_key_false(&__tracepoint_##name.key))		\
> +			__DO_TRACE(&__tracepoint_##name,		\
> +				TP_PROTO(data_proto),			\
> +				TP_ARGS(data_args),			\
> +				TP_CONDITION(cond),			\
> +				rcu_irq_enter(),			\
> +				rcu_irq_exit());			\
> +	}								\
>  	static inline int						\
>  	register_trace_##name(void (*probe)(data_proto), void *data)	\
>  	{								\