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

From: Peter Zijlstra <peterz@infradead.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	"Ingo Molnar" <mingo@redhat.com>,
	"James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>,
	"Helge Deller" <deller@gmx.de>,
	"Michael Ellerman" <mpe@ellerman.id.au>,
	"Benjamin Herrenschmidt" <benh@kernel.crashing.org>,
	"Paul Mackerras" <paulus@samba.org>,
	"Paul Walmsley" <paul.walmsley@sifive.com>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Albert Ou" <aou@eecs.berkeley.edu>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Borislav Petkov" <bp@alien8.de>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	"Josh Poimboeuf" <jpoimboe@redhat.com>,
	"Jiri Kosina" <jikos@kernel.org>,
	"Miroslav Benes" <mbenes@suse.cz>,
	"Petr Mladek" <pmladek@suse.com>,
	"Joe Lawrence" <joe.lawrence@redhat.com>,
	"Colin Ian King" <colin.king@canonical.com>,
	"Masami Hiramatsu" <mhiramat@kernel.org>,
	"Nicholas Piggin" <npiggin@gmail.com>,
	"Jisheng Zhang" <jszhang@kernel.org>,
	linux-csky@vger.kernel.org, linux-parisc@vger.kernel.org,
	linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org,
	live-patching@vger.kernel.org, 王贇 <yun.wang@linux.alibaba.com>,
	"Guo Ren" <guoren@kernel.org>
Subject: Re: [PATCH] tracing: Have all levels of checks prevent recursion
Date: Fri, 15 Oct 2021 20:24:59 +0200	[thread overview]
Message-ID: <20211015182459.GL174703@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20211015142033.72605b47@gandalf.local.home>

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@infradead.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;