Date: Mon, 25 Apr 2016 17:07:26 -0700
From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
Cc: David Ahern <dsahern@gmail.com>, Peter Zijlstra <peterz@infradead.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Ingo Molnar <mingo@kernel.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Brendan Gregg <brendan.d.gregg@gmail.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Alexei Starovoitov <ast@kernel.org>, He Kuang <hekuang@huawei.com>,
        Jiri Olsa <jolsa@redhat.com>, Masami Hiramatsu <mhiramat@kernel.org>,
        Milian Wolff <milian.wolff@kdab.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Stephane Eranian <eranian@google.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vince Weaver <vincent.weaver@maine.edu>,
        Wang Nan <wangnan0@huawei.com>, Zefan Li <lizefan@huawei.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH/RFC v2] perf core: Allow setting up max frame stack depth
 via sysctl
Message-ID: <20160426000724.GA28705@ast-mbp.thefacebook.com>
References: <20160422205232.GB7004@kernel.org>
 <571AA02B.90107@gmail.com>
 <20160422221806.GA62857@ast-mbp.thefacebook.com>
 <20160425161425.GA25218@kernel.org>
 <20160425162706.GB25218@kernel.org>
 <20160425192229.GC25218@kernel.org>
 <20160425200646.GA23875@ast-mbp.thefacebook.com>
 <20160425201750.GD25218@kernel.org>
 <20160425215947.GA25915@ast-mbp.thefacebook.com>
 <20160425234138.GA16708@kernel.org>
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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!