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Message-ID: <20071128223840.GA28007@kroah.com>
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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