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

[Robert P. J. Day]

On Sat, 28 May 2011, Belisko Marek wrote:

> Hi Robert,
>
> On Sat, May 28, 2011 at 5:15 PM, Robert P. J. Day <rpjday at 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;
> }

  i agree that there should be a "put_device(&dev->dev);" statement as
you show above.  however, i still don't see how this can be just a
stylistic improvement as you seem to suggest.  based on the warning
from the kernel source file, it would seem that you *must* do a
put_device() in that situation -- it's not optional.

rday

p.s.  i would also never do a memset() to zero, followed by a kfree(),
when a kzfree() is so much more concise.

-- 

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Robert P. J. Day                                 Ottawa, Ontario, CANADA
                        http://crashcourse.ca

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