linux-kernel - Re: [PATCH/RFC v2] perf core: Allow setting up max frame stack depth via sysctl

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Message-ID: <20160426000724.GA28705@ast-mbp.thefacebook.com>
Date:	Mon, 25 Apr 2016 17:07:26 -0700
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:	David Ahern <dsahern@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Brendan Gregg <brendan.d.gregg@...il.com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Alexei Starovoitov <ast@...nel.org>,
	He Kuang <hekuang@...wei.com>, Jiri Olsa <jolsa@...hat.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Milian Wolff <milian.wolff@...b.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Stephane Eranian <eranian@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vince Weaver <vincent.weaver@...ne.edu>,
	Wang Nan <wangnan0@...wei.com>, Zefan Li <lizefan@...wei.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH/RFC v2] perf core: Allow setting up max frame stack depth
 via sysctl

On Mon, Apr 25, 2016 at 08:41:39PM -0300, Arnaldo Carvalho de Melo wrote:
>  
> +int sysctl_perf_event_max_stack __read_mostly = PERF_MAX_STACK_DEPTH;
> +
> +static inline size_t perf_callchain_entry__sizeof(void)
> +{
> +	return (sizeof(struct perf_callchain_entry) +
> +		sizeof(__u64) * sysctl_perf_event_max_stack);
> +}
> @@ -1144,6 +1144,14 @@ static struct ctl_table kern_table[] = {
>  		.extra1		= &zero,
>  		.extra2		= &one_hundred,
>  	},
> +	{
> +		.procname	= "perf_event_max_stack",
> +		.data		= NULL, /* filled in by handler */
> +		.maxlen		= sizeof(sysctl_perf_event_max_stack),
> +		.mode		= 0644,
> +		.proc_handler	= perf_event_max_stack_handler,
> +		.extra1		= &zero,
> +	},

you need to define a max value otherwise perf_callchain_entry__sizeof
will overflow. Sure it's root only facility, but still not nice.
1M? Anything above 1M stack frames would be insane anyway.
The rest looks good. Thanks!