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

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Message-ID: <20190111024334.GA12140@osadl.at>
Date:   Fri, 11 Jan 2019 03:43:34 +0100
From:   Nicholas Mc Guire <der.herr@...r.at>
To:     Li Yang <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://lkml.org/lkml/2018/12/6/42
> > 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.

thx!
hofrat