linux-kernel - Re: [PATCH] p54usb: fix usb_kill_urb hang with slub

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Message-ID: <4939B6AF.2060901@lwfinger.net>
Date:	Fri, 05 Dec 2008 17:18:07 -0600
From:	Larry Finger <Larry.Finger@...inger.net>
To:	Greg KH <gregkh@...e.de>
CC:	Christian Lamparter <chunkeey@....de>,
	linux-wireless@...r.kernel.org,
	Johannes Berg <johannes@...solutions.net>,
	John W Linville <linville@...driver.com>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] p54usb: fix usb_kill_urb hang with slub_debug=P

Greg KH wrote:
> On Fri, Dec 05, 2008 at 03:47:45PM +0100, Christian Lamparter wrote:
>> This patch fixes a problem identified by Johannes Berg.
> 
> No, it only papers over the real problem here, let's work on a correct
> patch please.

I can contribute a little info. If SLUB debugging is enabled, and the boot
command includes 'slub_debug=P', I get a GPF in kref_get(), which is called from
kobject_get() with the following code:

        if (kobj)
                kref_get(&kobj->kref);

>From the dump, &kobj->kref is 0x6b6b6b6b6b6b6dbb, a poisoned value.

Somewhere, the "struct urb" has been freed, but kobj has not been set to NULL.

As everything I've found is a symptom, I'm still looking for the real cause.

Larry



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