linux-kernel - Re: [PATCH] counter: Set counter device name

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Date:   Fri, 4 Feb 2022 15:41:33 +0900
From:   William Breathitt Gray <vilhelm.gray@...il.com>
To:     Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Cc:     jic23@...nel.org, linux-iio@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] counter: Set counter device name

On Thu, Feb 03, 2022 at 10:00:53AM +0100, Uwe Kleine-König wrote:
> On Thu, Feb 03, 2022 at 04:34:59PM +0900, William Breathitt Gray wrote:
> > Naming the counter device provides a convenient way to identify it in
> > devres_log events and similar situations. This patch names the counter
> > device by combining the prefix "counter" with the counter device's
> > unique ID.
> > 
> > Cc: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> > Signed-off-by: William Breathitt Gray <vilhelm.gray@...il.com>
> > ---
> >  drivers/counter/counter-core.c | 12 +++++++++++-
> >  1 file changed, 11 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/counter/counter-core.c b/drivers/counter/counter-core.c
> > index 7e0957eea094..2ebd9adf0bd2 100644
> > --- a/drivers/counter/counter-core.c
> > +++ b/drivers/counter/counter-core.c
> > @@ -22,6 +22,8 @@
> >  #include "counter-chrdev.h"
> >  #include "counter-sysfs.h"
> >  
> > +#define COUNTER_NAME	"counter"
> > +
> >  /* Provides a unique ID for each counter device */
> >  static DEFINE_IDA(counter_ida);
> >  
> > @@ -104,6 +106,10 @@ struct counter_device *counter_alloc(size_t sizeof_priv)
> >  		goto err_ida_alloc;
> >  	dev->id = err;
> >  
> > +	err = dev_set_name(dev, COUNTER_NAME "%d", dev->id);
> > +	if (err)
> > +		goto err_dev_set_name;
> > +
> >  	mutex_init(&counter->ops_exist_lock);
> >  	dev->type = &counter_device_type;
> >  	dev->bus = &counter_bus_type;
> > @@ -119,6 +125,9 @@ struct counter_device *counter_alloc(size_t sizeof_priv)
> >  
> >  err_chrdev_add:
> >  
> > +	kfree(dev_name(dev));
> > +err_dev_set_name:
> > +
> 
> I think this is wrong as kobject_cleanup frees the name.
> 
> Best regards
> Uwe

This is true once the device is initialized by device_initialize() but
that won't happen until after counter_chrdev_add() is called; if
counter_chrdev_add() fails, we need to free this memory lest it leak
when we return the error code.

I did notice kobject_cleanup() calls kfree_const() on the name rather
than kfree(). Would it make sense to change this patch to call
kfree_const() instead?

William Breathitt Gray

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