Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753105AbcDVWFg (ORCPT ); Fri, 22 Apr 2016 18:05:36 -0400 Received: from mail-io0-f178.google.com ([209.85.223.178]:36271 "EHLO mail-io0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751719AbcDVWFe (ORCPT ); Fri, 22 Apr 2016 18:05:34 -0400 Subject: Re: [PATCH/RFC v2] perf core: Allow setting up max frame stack depth via sysctl To: Arnaldo Carvalho de Melo , Alexei Starovoitov References: <20160420224730.GX3677@kernel.org> <20160420230410.GA41736@ast-mbp.thefacebook.com> <20160422205232.GB7004@kernel.org> Cc: Peter Zijlstra , Frederic Weisbecker , Ingo Molnar , Adrian Hunter , Brendan Gregg , Alexander Shishkin , Alexei Starovoitov , He Kuang , Jiri Olsa , Masami Hiramatsu , Milian Wolff , Namhyung Kim , Stephane Eranian , Thomas Gleixner , Vince Weaver , Wang Nan , Zefan Li , Linux Kernel Mailing List From: David Ahern Message-ID: <571AA02B.90107@gmail.com> Date: Fri, 22 Apr 2016 16:05:31 -0600 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:38.0) Gecko/20100101 Thunderbird/38.7.2 MIME-Version: 1.0 In-Reply-To: <20160422205232.GB7004@kernel.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2490 Lines: 70 On 4/22/16 2:52 PM, Arnaldo Carvalho de Melo wrote: > Em Wed, Apr 20, 2016 at 04:04:12PM -0700, Alexei Starovoitov escreveu: >> On Wed, Apr 20, 2016 at 07:47:30PM -0300, Arnaldo Carvalho de Melo wrote: > >> Nice. I like it. That's a great approach to hard problem. >> Java guys will be happy too. >> Please also adjust two places in kernel/bpf/stackmap.c > >>> + { >>> + .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, > >> zero seems to be the wrong minimum. I think it should be at least 2 to >> to fit user/kernel tags ? Probably needs to define max as well. > > So, if someone asks for zero, it will not copy anything, but then, this > would be what the user had asked for :-) > > Ditto for the max, if someone asks for too big a callchain, then when > allocating it it will fail and no callchain will be produced, that or it > will be able to allocate but will take too long copying that many > addresses, and we would be prevented from doing so by some other > protection, iirc there is perf_cpu_time_max_percent, and then buffer > space will run out. > > So I think that leaving it as is is enough, no? > > Can I keep your Acked-by? David, can I keep yours? Yes > diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c > index 343c22f5e867..6fe77349fa9d 100644 > --- a/kernel/events/callchain.c > +++ b/kernel/events/callchain.c > @@ -18,6 +18,14 @@ struct callchain_cpus_entries { > struct perf_callchain_entry *cpu_entries[0]; > }; > > +int sysctl_perf_event_max_stack __read_mostly = PERF_MAX_STACK_DEPTH; > + > +static size_t perf_callchain_entry__sizeof(void) > +{ > + return sizeof(struct perf_callchain_entry) + > + sizeof(__u64) * sysctl_perf_event_max_stack; > +} > + To Alexei's comment, a max_stack of 0 still has a non-zero alloc size so that should be ok. > static DEFINE_PER_CPU(int, callchain_recursion[PERF_NR_CONTEXTS]); > static atomic_t nr_callchain_events; > static DEFINE_MUTEX(callchain_mutex); > @@ -73,7 +81,7 @@ static int alloc_callchain_buffers(void) > if (!entries) > return -ENOMEM; > > - size = sizeof(struct perf_callchain_entry) * PERF_NR_CONTEXTS; > + size = perf_callchain_entry__sizeof() * PERF_NR_CONTEXTS; > > for_each_possible_cpu(cpu) { > entries->cpu_entries[cpu] = kmalloc_node(size, GFP_KERNEL,