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

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Date:	Wed, 28 Nov 2007 17:00:57 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Greg KH <greg@...ah.com>
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, 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.

In any case, the change to kset_init() in my patch fixes a real bug.  
It never did set the ktype at all.

Alan Stern

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