Re: [PATCH/RFC v3] perf core: Allow setting up max frame stack depth via sysctl

[Arnaldo Carvalho de Melo]

Em Mon, Apr 25, 2016 at 05:44:00PM -0700, Alexei Starovoitov escreveu:
> On Mon, Apr 25, 2016 at 09:29:28PM -0300, Arnaldo Carvalho de Melo wrote:
> > Em Mon, Apr 25, 2016 at 05:07:26PM -0700, Alexei Starovoitov escreveu:
> > > > +	{
> > > > +		.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!
> > 
> > Something else? ;-)
> 
> all looks good to me. Thanks a bunch!

Thanks for checking!
 
> >     Because we only allocate the callchain percpu data structures when there
> >     is a user, which allows for changing the max easily, its just a matter
> >     of having no callchain users at that point.
> >     
> >     Reported-and-Tested-by: Brendan Gregg <brendan.d.gregg@xxxxxxxxx>
> >     Acked-by: Alexei Starovoitov <ast@xxxxxxxxxx>
> 
> yep :)
> hopefully Brendan can give it another spin.

Agreed, and I'm calling it a day anyway, Brendan, please consider
retesting, thanks,

- Arnaldo