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

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Date:	Wed, 28 Nov 2007 14:38:40 -0800
From:	Greg KH <greg@...ah.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Kay Sievers <kay.sievers@...y.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Jonathan Corbet <corbet@....net>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Cornelia Huck <cornelia.huck@...ibm.com>
Subject: Re: [PATCH] kobject: make sure kobj->ktype is set before
	kobject_init

On Wed, Nov 28, 2007 at 05:00:57PM -0500, Alan Stern wrote:
> On Wed, 28 Nov 2007, Greg KH wrote:
> 
> > On Wed, Nov 28, 2007 at 03:42:00PM -0500, Alan Stern wrote:
> > > This patch (as1020) adds a check to kobject_init() to insure that the
> > > ktype field is not NULL.  This is just for safety's sake; as far as I
> > > know there are no remaining places where the field is left unset.  But
> > > ironically, kset_init() did fail to set it!  The patch fixes that and
> > > removes some redundant initialization in kset_createa().
> > > 
> > > The patch also fixes up elevator_init(), where ktype was set after
> > > calling kobject_init() instead of before.
> > 
> > No, it's safe to set ktype after kobject_init, it was just not safe to
> > set the kset.  As Kay pointed out, I just added a patch to my tree to
> > resolve this issue, and I'll go back and update the documentation now.
> > 
> > I do like the "check for a ktype" warning, I'll go add that to my local
> > tree and see what breaks.  Odds are, all the static kobjects will :(
> 
> You have to be careful.  The ktype check I wrote lives in
> kobject_init() -- that's why I had to make elevator_init() assign the
> ktype before calling kobject_init().  If you put the check into
> kobject_add() instead then you won't end up checking objects that get
> initialized but not added.
> 
> Yes, nobody would deliberately use a kobject without adding it, but it 
> could happen as the result of an failure between the _init and _add 
> calls.

No, people do deliberately do this.  Right now, after a few cleanup
patches in my tree, there are only two users who create kobjects but do
not register them, struct cdev and the kobj_map stuff.

The cdev code I'll work on cleaning up, there's just some historical
usages there that I've never felt all that comfortable with, and the
kobj_map code I'd like to convert to just use a list and a kref and not
a kobject at all so that I stop getting emails about it over time :)

thanks,

greg k-h
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