Re: [PATCH] kobject: make sure kobj->ktype is set before kobject_init

Alan Stern
2007-11-29T18:05:16Z

On Thu, 29 Nov 2007, Kay Sievers wrote:

> > > Sounds fine, maybe we should also pass the name along, so it will be
> > > obvious what happens here:
> > > int kobject_init(struct kobject *kobj, struct kobj_type *type, const char *fmt, ...)
> >
> > I don't know... Normally *_init() routines can't fail, but this could.
> > Then things like device_register() would run into trouble: The caller
> > wouldn't know whether a failure occurred before or after the
> > kobject_init() call, so it wouldn't know what sort of cleanup action
> > was needed: kfree() or device_put().
>
> But wouldn't device_register() do the kobject cleanup for you when it
> fails? Why would a caller of device_register() care about the state of
> the kobject?

Let's say device_register() calls device_init(), which calls
kobject_init(), which fails. Then there's no cleanup to do --
device_register() returns -ENOMEM or some such code and the caller has
to do the kfree().

Now let's say device_register() calls device_init(), which succeeds,
and then calls device_add(), which fails. To recover properly,
somebody then has to call device_put(). That "somebody" can't be the
original caller -- according to the previous paragraph the original
caller won't do anything but kfree(). So the "somebody" has to be
device_register() itself.

But the device_put() will call kobject_put(), which will invoke the
device's cleanup routine, which will deallocate the structure. Now the
original caller gets an error code (perhaps -ENOMEM again) but must
_not_ call kfree().

So what should the original caller do when an error occurs?

Alan Stern