linux-kernel - Re: kobject must be initialized before calling kobject

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Message-ID: <20080209051539.GA28565@kroah.com>
Date:	Fri, 8 Feb 2008 21:15:39 -0800
From:	Greg KH <greg@...ah.com>
To:	Roland Dreier <rdreier@...co.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: kobject must be initialized before calling kobject_init()?!

On Fri, Feb 08, 2008 at 08:24:25PM -0800, Roland Dreier wrote:
> So I was perusing the code in lib/kobject.c, and I saw this:
> 
> 	void kobject_init(struct kobject *kobj, struct kobj_type *ktype)
> 	{
> 		// [a couple of of parameter checks...]
> 		if (kobj->state_initialized) {
> 			/* do not error out as sometimes we can recover */
> 			printk(KERN_ERR "kobject (%p): tried to init an initialized "
> 			       "object, something is seriously wrong.\n", kobj);
> 			dump_stack();
> 		}
> 
> in other words the first thing you do is check a member of the
> structure you're supposed to be initializing -- if someone just
> kmalloc()s a struct kobject and passes it into this function, there's
> a good chance that state_initialized won't be zero.  In fact, with
> slab debugging on, it's guaranteed to be poisoned with a non-zero
> value.
> 
> So are users supposed to be zeroing out struct kobjects before
> initializing them?

Yes.  See also the check about the non-zero reference count when
initializing the kref, that too will trip.

> If so, this should probably be documented.

You're right.  Patches gladly accepted :)

thanks,

greg k-h
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