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From: Ondrej Zary <linux@rainbow-software.org>
To: Oliver Neukum <oliver@neukum.org>
Subject: Re: debugging oops after disconnecting Nexio USB touchscreen
Date: Thu, 3 Dec 2009 10:30:21 +0100
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Cc: Alan Stern <stern@rowland.harvard.edu>, linux-usb@vger.kernel.org,
       linux-kernel@vger.kernel.org
References: <Pine.LNX.4.44L0.0912011005140.2983-100000@iolanthe.rowland.org> <200912020952.09354.linux@rainbow-software.org> <200912021042.04557.oliver@neukum.org>
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On Wednesday 02 December 2009, Oliver Neukum wrote:
> Am Mittwoch, 2. Dezember 2009 09:52:08 schrieb Ondrej Zary:
> > It shows "prev is NULL, qh=f6581080, ehci->async=f6581000".
> >
> > The problem is that activating usbmon causes the problem to disappear. No
> >  errors in maybe 15 attempts. It appeared on 2nd attempt after unloading
> >  usbmon.
>
> That suggests a use after free bug, which usbmon prevents holding
> an additional reference.
> Are you using SLAB_DEBUG?

Just tried 2.6.32-rc8-next-20091202 with SLAB_DEBUG enabled and got this:

BUG: unable to handle kernel paging request at 6b6b6b6b
IP: [<f7c649a3>] qh_completions+0x6c/0x400

Call Trace:
lapic_next_event
ehci_work
tick_dev_program_event
tick_program_event
hrtimer_interrupt
ehci_watchdog+0x0/0x37
ehci_watchdog+0x2b/0x37
run_timer_softirq
__do_softirq
irq_exit
do_IRQ
common_interrupt
acpi_idle_enter_bm
cpuidle_idle_call
cpu_idle
start_kernel

Code: 00 00 00 00 3c 03 88 44 24 1f 0f 94 c0 81 ea ec 00 00 00 0f b6 c0 89 44 
24 14 89 14 24 8b 46 0c 31 db bd 8d ff ff ff c6 46 28 00 <8b> 08 89 4c 24 10 
e9 ec 02 00 00 83 e8 38 85 db 89 44 24 24 8b


-- 
Ondrej Zary
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