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

[Alexei Starovoitov]

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!