linux-kernel - Re: get_device

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Date:	Mon, 5 Oct 2009 20:05:13 -0700
From:	Greg KH <greg@...ah.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Colin Guthrie <cguthrie@...driva.org>,
	Kay Sievers <kay.sievers@...y.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: get_device_parent() race bug

On Tue, Oct 06, 2009 at 10:15:12AM +0900, Tejun Heo wrote:
> Greg KH wrote:
> >>>  BUG: unable to handle kernel NULL pointer dereference at 0000000000000038
> >> Ping.  This one needs to be fixed in -stable.  It can be triggered by
> >> other char devices too.
> >
> > Sorry, been slowly catching up...
> > 
> > This can be triggered by char devices?  Huh?  How?  I don't see the
> > failure path that is happening here.
> 
> Oooh, s/char/virtual/.  The bug is in the path which creates a
> directory under the phony parent.
> 
> > And char devices shouldn't really be using the kobject at all, except
> > for a very basic reference count.
> > 
> > I keep threatening to rip kobject out of a char device and just use a
> > kref, as that is all that is really needed.  Well, that and the kmap
> > stuff, but again, it's not a "real" kobject being used there...
> > 
> > Perhaps now is the time to do this.
> 
> Yay!

Ugh, I tried to do this today but it looks like the gendisk structure
got all tied up with the kobj_map logic.  Which doesn't look all too
correct to me but I'm not sure.

Kay, you did the gendisk kobject conversion, right?  Any reason you tied
it into the kobj_map stuff?  Or was that the way the code always was?

thanks,

greg k-h
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