should failed calls to device_register() always call put_device()?

From: marek.belisko@gmail.com (Belisko Marek)
To: kernelnewbies@lists.kernelnewbies.org
Subject: should failed calls to device_register() always call put_device()?
Date: Sat, 28 May 2011 18:00:10 +0200	[thread overview]
Message-ID: <BANLkTimSfBQ1JO9+TbdApgFXfqTM=a55nQ@mail.gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.00.1105281106220.5308@localhost6.localdomain6>

Hi Robert,

On Sat, May 28, 2011 at 5:15 PM, Robert P. J. Day <rpjday@crashcourse.ca> wrote:
>
> ?from drivers/base/core.c, we have the fairly unambiguous advice:
>
> * NOTE: _Never_ directly free @dev after calling this function, even
> * if it returned an error! Always use put_device() to give up the
> * reference initialized in this function instead.
> */
> int device_register(struct device *dev)
> {
> ? ? ? ?device_initialize(dev);
> ? ? ? ?return device_add(dev);
> }
>
> ?and yet, there appears to be driver code that does exactly that,
> such as this snippet from drivers/w1/w1_int.c (line 86):
>
> ? ? ? ?... snip ...
> ? ? ? ?err = device_register(&dev->dev);
> ? ? ? ?if (err) {
> ? ? ? ? ? ? ? ?printk(KERN_ERR "Failed to register master device. err=%d\n", err);
> ? ? ? ? ? ? ? ?memset(dev, 0, sizeof(struct w1_master));
> ? ? ? ? ? ? ? ?kfree(dev);
> ? ? ? ? ? ? ? ?dev = NULL;
> ? ? ? ?}
Free is for allocated dev not for struct device so it is OK. IMO thi
snippet should look like:
err = device_register(&dev->dev);
if (err) {
    printk(KERN_ERR "Failed to register master device. err=%d\n", err);
    put_device(&dev->dev);
    memset(dev, 0, sizeof(struct w1_master));
    kfree(dev);
    dev = NULL;
}

>
> ? ? ? ?return dev;
>
> ?isn't the above doing just that -- directly freeing the dev
> structure without first calling put_device()? ?or am i misreading
> something?
>
> rday
>
> --
>
> ========================================================================
> Robert P. J. Day ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? Ottawa, Ontario, CANADA
> ? ? ? ? ? ? ? ? ? ? ? ?http://crashcourse.ca
>
> Twitter: ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? http://twitter.com/rpjday
> LinkedIn: ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? http://ca.linkedin.com/in/rpjday
> ========================================================================
>
>
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>
regards,

marek

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