linux-kernel - Re: [PATCH] tracing: Have all levels of checks prevent recursion

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Date:   Fri, 15 Oct 2021 20:24:59 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
        Helge Deller <deller@....de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Colin Ian King <colin.king@...onical.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Jisheng Zhang <jszhang@...nel.org>, linux-csky@...r.kernel.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-riscv@...ts.infradead.org, live-patching@...r.kernel.org,
        王贇 <yun.wang@...ux.alibaba.com>,
        Guo Ren <guoren@...nel.org>
Subject: Re: [PATCH] tracing: Have all levels of checks prevent recursion

On Fri, Oct 15, 2021 at 02:20:33PM -0400, Steven Rostedt wrote:
> On Fri, 15 Oct 2021 20:04:29 +0200
> Peter Zijlstra <peterz@...radead.org> 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;