linux-kernel - Re: get_device

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Message-ID: <20091005142201.GA21891@kroah.com>
Date:	Mon, 5 Oct 2009 07:22:01 -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 Sun, Oct 04, 2009 at 09:35:35AM +0900, Tejun Heo wrote:
> Tejun Heo wrote:
> > Hello, Greg, Kay, Guthrie.
> > 
> > This problem was reported in bko#14023.  (aiee.. again, sorry about
> > the delay)
> > 
> >   http://bugzilla.kernel.org/show_bug.cgi?id=14023
> > 
> > sysfs is creating several devices in cuse class concurrently and with
> > CONFIG_SYSFS_DEPRECATED turned off, it triggers the following oops.
> > 
> >  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.

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.

thanks,

greg k-h
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