linux-kernel - Re: rmmod uhci_hcd -> BUG: atomic counter underflow

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Date:	Mon, 12 Mar 2007 14:41:49 -0700
From:	Greg KH <greg@...ah.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Jiri Slaby <jirislaby@...il.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>,
	USB development list <linux-usb-devel@...ts.sourceforge.net>
Subject: Re: rmmod uhci_hcd -> BUG: atomic counter underflow

On Mon, Mar 12, 2007 at 05:25:09PM -0400, Alan Stern wrote:
> On Mon, 12 Mar 2007, Jiri Slaby wrote:
> 
> > Jiri Slaby napsal(a):
> > > Alan Stern napsal(a):
> > >> On Mon, 12 Mar 2007, Jiri Slaby wrote:
> > >>> After rmmoding of uhci_hcd on fresh booted 2.6.21-rc3-mm2 I got this:
> > >>>
> > >>> BUG: atomic counter underflow at:
> > > [...]
> > >>>   [<c01db754>] kobject_put+0x14/0x16
> > >>>   [<c01db8a3>] kobject_unregister+0x22/0x25
> > >>>   [<c024c987>] bus_remove_driver+0x75/0x82
> > >>>   [<c024d3b8>] driver_unregister+0xb/0x18
> > >>>   [<c01e7020>] pci_unregister_driver+0x13/0x73
> > >>>   [<f88dbbd9>] uhci_hcd_cleanup+0xd/0x2d [uhci_hcd]
> > > [...]
> > >> Would it be possible for you to add the atomic counter underflow check 
> > >> to 2.6.21-rc3 and see if the problem still occurs?  If it doesn't, 
> > >> that's a good indication the USB stack isn't guilty -- the bus 
> > >> registration code hasn't changed for several kernel releases.
> > > 
> > > Yes.
> > 
> > I can confirm, that this issue went upstream and is currently present there.
> 
> I found the problem, but I don't know how to fix it.  Hopefully Greg or 
> Rusty will know.
> 
> There are two bugs in kernel/module.c:module_remove_driver(), right at the 
> end of the routine:
> 
> 	/*
> 	 * Undo the additional reference we added in module_add_driver()
> 	 * via kset_find_obj()
> 	 */
> 	if (drv->mod_name)
> 		kobject_put(&drv->kobj);
> 

This code is reverted in 2.6.21-rc3-git7 as it was incorrect as you have
properly determined.

So, can people please test with a kernel newer than that?

thanks,

greg k-h
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