linux-kernel - Re: [PATCH]s390/char/vmur.c: memory leak Fix in the driver

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Message-ID: <20120319120808.7e34d652@de.ibm.com>
Date:	Mon, 19 Mar 2012 12:08:08 +0100
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	"Chen, Dennis (SRDC SW)" <Dennis1.Chen@....com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"beattiem@...ibm.com" <beattiem@...ibm.com>,
	"holzheu@...ibm.com" <holzheu@...ibm.com>,
	"munzert@...ibm.com" <munzert@...ibm.com>,
	"linux390@...ibm.com" <linux390@...ibm.com>,
	"linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
	"heiko.carstens@...ibm.com" <heiko.carstens@...ibm.com>
Subject: Re: [PATCH]s390/char/vmur.c: memory leak Fix in the driver

On Mon, 19 Mar 2012 11:37:44 +0100
Martin Schwidefsky <schwidefsky@...ibm.com> wrote:

> On Mon, 19 Mar 2012 01:55:40 +0000
> "Chen, Dennis (SRDC SW)" <Dennis1.Chen@....com> wrote:
> 
> > CC'ing maintainer: Martin Schwidefsky &  Heiko Carstens...
> > 
> > -----Original Message-----
> > From: Chen, Dennis (SRDC SW) 
> > Sent: Sunday, March 18, 2012 3:41 AM
> > To: linux-kernel@...r.kernel.org
> > Cc: beattiem@...ibm.com; holzheu@...ibm.com; munzert@...ibm.com; linux390@...ibm.com; linux-s390@...r.kernel.org; Chen, Dennis (SRDC SW)
> > Subject: [PATCH]s390/char/vmur.c: memory leak Fix in the driver
> > 
> > This patch is used to fix a memory leak issue in s390/char/vmur.c: a character device instance is 
> > allocated by cdev_alloc, the cdev_del will not free that space if cdev_init is applied before. 
> > 
> > Signed-off-by: dennis1.chen@....com
> > --- a/s390/char/vmur.c  2012-03-18 02:50:47.950963949 +0800
> > +++ b/s390/char/vmur.c  2012-03-18 03:12:04.790936740 +0800
> > @@ -903,7 +903,7 @@ static int ur_set_online(struct ccw_devi
> >                 goto fail_urdev_put;
> >         }
> > 
> > -       cdev_init(urd->char_device, &ur_fops);
> > +       urd->char_device->ops = &ur_fops;
> >         urd->char_device->dev = MKDEV(major, minor);
> >         urd->char_device->owner = ur_fops.owner;
> > 
> 
> How does that fix anything? My copy of cdev_init looks like this:
> 
> void cdev_init(struct cdev *cdev, const struct file_operations *fops)
> {
>         memset(cdev, 0, sizeof *cdev);
>         INIT_LIST_HEAD(&cdev->list);
>         kobject_init(&cdev->kobj, &ktype_cdev_default);
>         cdev->ops = fops;
> }
> 
> It does not allocate anything but it initializes some more fields.
> The new code would only initialize the ops field. In addition
> cdev_del does a kobject_put and the release function of the object
> will call cdev_dynamic_release as far as I can tell. That code
> should be fine as it is.

Hmm, forget that. cdev_init has a second kobject_init that replaces
ktype_cdev_dynamic with ktype_cdev_default. cdev_alloc already does
the initialization and your fix is just fine. 
Seems like cdev_init is only there for static cdev structures.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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