From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752590AbeBWUvE (ORCPT ); Fri, 23 Feb 2018 15:51:04 -0500 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:59702 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752447AbeBWSbE (ORCPT ); Fri, 23 Feb 2018 13:31:04 -0500 Date: Fri, 23 Feb 2018 18:30:58 +0000 From: Lorenzo Pieralisi To: Rolf Evers-Fischer Cc: Kishon Vijay Abraham I , bhelgaas@google.com, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, Rolf Evers-Fischer Subject: Re: [PATCH 1/2] pci: endpoint: Free func_name after last usage Message-ID: <20180223183058.GA11698@e107981-ln.cambridge.arm.com> References: <20180221124707.26308-1-embedded24@evers-fischer.de> <20180221124707.26308-2-embedded24@evers-fischer.de> <20180222181901.GA13694@e107981-ln.cambridge.arm.com> <9cdc8c1c-b448-b00b-d5b8-b664bd96f856@ti.com> <20180223093611.GA25086@e107981-ln.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 23, 2018 at 06:38:42PM +0100, Rolf Evers-Fischer wrote: > Hi Kishon, > > On Fri, 23 Feb 2018, Kishon Vijay Abraham I wrote: > > On Friday 23 February 2018 03:06 PM, Lorenzo Pieralisi wrote: > > > On Fri, Feb 23, 2018 at 11:40:49AM +0530, Kishon Vijay Abraham I wrote: > > >> Hi Lorenzo, > > >> > > >> On Thursday 22 February 2018 11:49 PM, Lorenzo Pieralisi wrote: > > >>> On Wed, Feb 21, 2018 at 01:47:06PM +0100, Rolf Evers-Fischer wrote: > > >>>> From: Rolf Evers-Fischer > > >>>> > > >>>> This commit decreases the number of jump labels and ensures > > >>>> that the next commit doesn't increase the number of occurrences > > >>>> of 'kfree(func_name)'. > > >>>> > > >>>> Change-Id: I0d1b6fd652395b85f82b11c43bf9b7db512854d1 > > >>>> Signed-off-by: Rolf Evers-Fischer > > >>>> Signed-off-by: Rolf Evers-Fischer > > >>>> --- > > >>>> drivers/pci/endpoint/pci-epf-core.c | 7 ++----- > > >>>> 1 file changed, 2 insertions(+), 5 deletions(-) > > >>>> > > >>>> diff --git a/drivers/pci/endpoint/pci-epf-core.c b/drivers/pci/endpoint/pci-epf-core.c > > >>>> index 766ce1dca2ec..23d0e128d1a5 100644 > > >>>> --- a/drivers/pci/endpoint/pci-epf-core.c > > >>>> +++ b/drivers/pci/endpoint/pci-epf-core.c > > >>>> @@ -220,9 +220,10 @@ struct pci_epf *pci_epf_create(const char *name) > > >>>> *buf = '\0'; > > >>>> > > >>>> epf->name = kstrdup(func_name, GFP_KERNEL); > > >>>> + kfree(func_name); > > >>> > > >>> I am certainly missing something but what if we reworked the code > > >>> and just: > > >>> > > >>> kstrdup(name, GFP_KERNEL); > > >>> > > >>> once instead of allocating another local copy (that we then have to > > >>> free) ? > > >> > > >> name will be something like pci_epf_test.0 and in epf->name we want to just > > >> have pci_epf_test. > > >>> > > >>> Reworded: why > > >>> > > >>> epf->name = func_name; > > >> > > >> memory should be allocated for epf->name before it can be initialized. IMO > > >> without kstrdup, there will be a null pointer exception. > > > > > > I understand that but the point is that func_name *was* allocated with > > > kstrdup() already I would like to understand why we need to do it twice > > > (and kfree the first allocation). > > > > func_name would be allocated for a size greater than what will be in epf->name. > > It won't be significant though. > > > > Thanks > > Kishon > > > I have just an idea, how to use only one copy, but with the shorter > length. What about changing the code like this? > int len = strchrnul(name, '.') - name; > epf->name = kstrndup(name, len, GFP_KERNEL); > > In this case we are only allocating the smaller amount of memory and we > don't need the 'buf' and 'func_name' pointers anymore. They will be > replaced with 'len' and some pointer arithmetic. Yes, something along those lines, I do not see the point of having to allocate two buffers (and actually this simplifies the error path too). Thanks, Lorenzo