Subject: Re: [PATCH] tracing: Have all levels of checks prevent recursion

From: Peter Zijlstra <[email-masked]>
Date: Fri, 15 Oct 2021 20:24:59 +0200

On Fri, Oct 15, 2021 at 02:20:33PM -0400, Steven Rostedt wrote:
> On Fri, 15 Oct 2021 20:04:29 +0200
> Peter Zijlstra <[email-masked]> wrote:
> 
> > On Fri, Oct 15, 2021 at 01:58:06PM -0400, Steven Rostedt wrote:
> > > Something like this:  
> > 
> > I think having one copy of that in a header is better than having 3
> > copies. But yes, something along them lines.
> 
> I was just about to ask you about this patch ;-)

Much better :-)

> diff --git a/kernel/events/internal.h b/kernel/events/internal.h
> index 228801e20788..c91711f20cf8 100644
> --- a/kernel/events/internal.h
> +++ b/kernel/events/internal.h
> @@ -206,11 +206,7 @@ DEFINE_OUTPUT_COPY(__output_copy_user, arch_perf_out_copy_user)
>  static inline int get_recursion_context(int *recursion)
>  {
>  	unsigned int pc = preempt_count();

Although I think we can do without that ^ line as well :-)

> -	unsigned char rctx = 0;
> -
> -	rctx += !!(pc & (NMI_MASK));
> -	rctx += !!(pc & (NMI_MASK | HARDIRQ_MASK));
> -	rctx += !!(pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET));
> +	unsigned char rctx = interrupt_context_level();
>  
>  	if (recursion[rctx])
>  		return -1;