linux-kernel - RE: [PATCH] soc: fsl: guts: us devm_kstrdup

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Message-ID: <AM6PR04MB5863821216050C13EBED68AA8F850@AM6PR04MB5863.eurprd04.prod.outlook.com>
Date:   Fri, 11 Jan 2019 21:32:53 +0000
From:   Leo Li <leoyang.li@....com>
To:     Nicholas Mc Guire <der.herr@...r.at>
CC:     Scott Wood <oss@...error.net>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        Nicholas Mc Guire <hofrat@...dl.org>
Subject: RE: [PATCH] soc: fsl: guts: us devm_kstrdup_const() for RO data



> -----Original Message-----
> From: Nicholas Mc Guire <der.herr@...r.at>
> Sent: Thursday, January 10, 2019 8:44 PM
> To: Leo Li <leoyang.li@....com>
> Cc: Scott Wood <oss@...error.net>; linuxppc-dev <linuxppc-
> dev@...ts.ozlabs.org>; lkml <linux-kernel@...r.kernel.org>; moderated
> list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE <linux-arm-
> kernel@...ts.infradead.org>; Nicholas Mc Guire <hofrat@...dl.org>
> Subject: Re: [PATCH] soc: fsl: guts: us devm_kstrdup_const() for RO data
> 
> On Thu, Jan 10, 2019 at 01:43:01PM -0600, Li Yang wrote:
> > On Sat, Dec 22, 2018 at 2:02 AM Nicholas Mc Guire <der.herr@...r.at>
> wrote:
> > >
> > > On Fri, Dec 21, 2018 at 08:29:56PM -0600, Scott Wood wrote:
> > > > On Fri, 2018-12-07 at 09:22 +0100, Nicholas Mc Guire wrote:
> > > > > devm_kstrdup() may return NULL if internal allocation failed,
> > > > > but as  machine  is from the device tree, and thus RO,
> > > > > devm_kstrdup_const() can be used here, which will only copy the
> reference.
> > > >
> > > > Is it really going to only copy the reference?  That would require
> > > > that
> > > > is_kernel_rodata(machine) be true, which it shouldn't be since
> > > > it's not part of the kernel image.
> > > >
> > > I had tried to figure out what is RO and what not but was not able
> > > to determine that - from the discussion it seemed that the
> > > assumption of RO is correct though I did not ask if it would satisfy
> > > is_kernel_rodata() so that explains the incorrect assertion.
> > > see
> > >
> https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fl
> > >
> kml.org%2Flkml%2F2018%2F12%2F6%2F42&amp;data=02%7C01%7Cleoyang.l
> i%40
> > >
> nxp.com%7Cf72d70a65d1b47f6883808d6776e9d58%7C686ea1d3bc2b4c6fa92c
> d99
> > >
> c5c301635%7C0%7C1%7C636827714307963102&amp;sdata=xnaO0Y7q%2Byad
> Yv8sF
> > > VPFtkfllgnwpEIkkTIgw0K%2Fovg%3D&amp;reserved=0
> > > So then the only option is to check the return and cleanup on
> > > allocation failure as the orriginal patch proposed.
> >
> > Thanks for the good discussion. I will drop the previous patch. But
> > would it also be good to just have "soc_dev_attr.machine = machine"
> > directly?
> >
> I think that the intent is to switch to managed devm API so that the cleanup is
> handled properly currently you would get "machine" from
> of_property_read_string_index
>   -> of_property_read_string_helper
>    -> of_find_property
> which does not do any allocation - so there would actually not be anything to
> cleanup here - don´t see why your solution would not be suitable given the
> current API. the only advantage of the devm_kstrdup() is that underlying
> APIs internal changes would have no effect.

Thanks.  I will sent out a new version.

Regards,
Leo