From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754270AbaFTAN0 (ORCPT ); Thu, 19 Jun 2014 20:13:26 -0400 Received: from mail-yk0-f177.google.com ([209.85.160.177]:48710 "EHLO mail-yk0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751125AbaFTANZ (ORCPT ); Thu, 19 Jun 2014 20:13:25 -0400 Message-ID: <53A37CA2.9030200@gmail.com> Date: Thu, 19 Jun 2014 20:13:22 -0400 From: Pranith Kumar User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 MIME-Version: 1.0 To: paulmck@linux.vnet.ibm.com CC: Joe Perches , LKML , romanov.arya@gmail.com, Josh Triplett Subject: Re: [RFC PATCH] use snprintf instead of sprintf in rcu_torture_printk References: <1402419340.30479.18.camel@joe-AO725> <20140611074704.GS5015@mwanda> <1402502500.6169.5.camel@joe-AO725> <20140618193345.GR4669@linux.vnet.ibm.com> <1403120982.3839.25.camel@joe-AO725> <20140619210031.GN4904@linux.vnet.ibm.com> <53A37140.3020003@gmail.com> <20140619234922.GY4904@linux.vnet.ibm.com> In-Reply-To: <20140619234922.GY4904@linux.vnet.ibm.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/19/2014 07:49 PM, Paul E. McKenney wrote: > On Thu, Jun 19, 2014 at 07:24:48PM -0400, Pranith Kumar wrote: >> (dropping some CCs) >> >> On 06/19/2014 05:00 PM, Paul E. McKenney wrote: >>> On Wed, Jun 18, 2014 at 12:49:42PM -0700, Joe Perches wrote: >>>> >>>> I believe the function doesn't work well. >>>> >>>> static void >>>> rcu_torture_stats_print(void) >>>> { >>>> int size = nr_cpu_ids * 200 + 8192; >>>> char *buf; >>>> >>>> buf = kmalloc(size, GFP_KERNEL); >>>> if (!buf) { >>>> pr_err("rcu-torture: Out of memory, need: %d\n", size); >>>> return; >>>> } >>>> rcu_torture_printk(buf); >>>> pr_alert("%s", buf); >>>> kfree(buf); >>>> } >>>> >>>> rcu_torture_printk simply fills buf >>>> >>>> btw: I believe the arguments should pass size and >>>> rcu_torture_printk should use snprintf/size >>>> >>>> but all printks are limited to a maximum of 1024 >>>> bytes so the large allocation is senseless and >>>> would even if it worked, would likely need to be >>>> vmalloc/vfree >>> >>> Fair point! >>> >>> Pranith, Romanov, if you would like part of RCU that is less touchy >>> about random hacking, this would be a good place to start. Scripts in >>> tools/testing/selftests/rcutorture/bin do care about some of the format, >>> but the variable-length portion generated by cur_ops->stats() is as far >>> as I know only parsed by human eyes. >>> >> >> Here is a first run of the change. Please let me know if I am totally off. RFC. :) > > Thank you for taking this on! You are most welcome :) > >> Three things on Todo list: >> >> * We need to check that we are using less than the allocated size of the buffer (used > size). (we are allocating a big buffer, so not sure if necessary) >> * Need to check with the scripts if they are working. >> * I used a loop for pr_alert(). I am not sure this is right, there should be a better way for printing large buffers >> >> If the overall structure is ok I will go ahead and check how the scripts are handling these changes. > > One other thing... Convince this function (and a few others that it > calls) that the system really has 4096 CPUs, run this code, and see what > actually happens both before and after. Just to get a bit of practice > mixed in with the theory. ;-) > OK. I think to do this I need to use 4096 instead of nr_cpu_ids. I will try this and see how it goes :) -- Pranith