linux-kernel - Re: [PATCH] i2c: mux: demux-pinctrl: handle failure case of devm

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Message-ID: <20181204121318.GB28201@osadl.at>
Date:   Tue, 4 Dec 2018 13:13:18 +0100
From:   Nicholas Mc Guire <der.herr@...r.at>
To:     Peter Rosin <peda@...ntia.se>
Cc:     Nicholas Mc Guire <hofrat@...dl.org>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] i2c: mux: demux-pinctrl: handle failure case of
 devm_kstrdup()

On Tue, Dec 04, 2018 at 11:16:59AM +0000, Peter Rosin wrote:
> Hi!
> 
> This patch looks like a good idea. However, a nitpick below.
> 
> On 2018-12-01 11:01, Nicholas Mc Guire wrote:
> > devm_kstrdup() may return NULL if internal allocation failed.
> > Thus using  name, value  is unsafe without being checked. As
> > i2c_demux_pinctrl_probe() can return -ENOMEM in other cases
> > a dev_err() message is included to make the failure location
> > clear.
> > 
> > Signed-off-by: Nicholas Mc Guire <hofrat@...dl.org>
> > Fixes: e35478eac030 ("i2c: mux: demux-pinctrl: run properly with multiple instances")
> > ---
> > 
> > Problem located with experimental coccinelle script
> > 
> > Q: The use of devm_kstrdup() seems a bit odd while technically not wrong,
> >    personally I think devm_kasprintf() would be more suitable here.
> > 
> > Patch was compile tested with: multi_v7_defconfig 
> > (implies I2C_DEMUX_PINCTRL=y)
> > 
> > Patch is against 4.20-rc4 (localversion-next is next-20181130)
> > 
> >  drivers/i2c/muxes/i2c-demux-pinctrl.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/drivers/i2c/muxes/i2c-demux-pinctrl.c b/drivers/i2c/muxes/i2c-demux-pinctrl.c
> > index 035032e..c466999 100644
> > --- a/drivers/i2c/muxes/i2c-demux-pinctrl.c
> > +++ b/drivers/i2c/muxes/i2c-demux-pinctrl.c
> > @@ -244,6 +244,12 @@ static int i2c_demux_pinctrl_probe(struct platform_device *pdev)
> >  
> >  		props[i].name = devm_kstrdup(&pdev->dev, "status", GFP_KERNEL);
> >  		props[i].value = devm_kstrdup(&pdev->dev, "ok", GFP_KERNEL);
> > +		if (!props[i].name || !props[i].value) {
> > +			dev_err(&pdev->dev,
> > +				"chan %d name, value allocation failed\n", i);
> 
> Please drop this memory allocation failure message. You should get such a
> message from devm_kstrdup.
>

hm...tried to figure out where that message would be comming
from - but I could not find any point in the call tree that
would issue such a message ?

 devm_kstrdup() 
   -> devm_kmalloc()
        -> alloc_dr()
             --> kmalloc_track_caller() (non-NUMA)
             |     -> __kmalloc_node()
             |        -> __do_kmalloc_node()
             `-> __kmalloc_node_track_caller() (NUMA)
                   -> __do_kmalloc_node()

 __do_kmalloc_node() seems like it simply returns NULL but
 issues no failure message.
 Am I overlooking something ? 

thx!
hofrat 
 
> Cheers,
> Peter
> 
> > +			err = -ENOMEM;
> > +			goto err_rollback;
> > +		}
> >  		props[i].length = 3;
> >  
> >  		of_changeset_init(&priv->chan[i].chgset);
> > 
>