Bug#498293: linux-image-2.6.26-1-686: mos7840 USB serial driver fails to work and causes kernel OOPS with 2.6.26-4
On Mon, Sep 08, 2008 at 08:38:20PM +0100, Nick Leverton wrote:
> Package: linux-image-2.6.26-1-686
> Version: 2.6.26-4
> Severity: serious
> Justification: lenny/rc-policy
>
> I have a USB "Express" twin port serial adaptor, which identifies itself
> as USB ID 9710:7840 MosChip Semiconductor. This uses the mos7840 Moschip
> 7840/7820 USB Serial Driver.
>
> On linux-image-2.6.26-1-686 version 2.6.26-3 this adaptor worked fine
> and neither of the following problems occurred.
>
> On linux-image-2.6.26-1-686 version 2.6.26-4 there are serious problems.
>
> First, the usb-serial ports do not work correctly. Whatever character
> I send to the tty, it emits the letter 'O' from the serial port.
> See the two strace attachments, which are from kernels 2.6.26-3 and
> 2.6.26-4 respectively. They were generated using minicom talking to a
> serial device which just echoes the input and sends the prompt "Ready"
> when it receives a carriage return.
>
> Unfortunately I didn't type the same characters in each test, but
> if you diff the straces you can see that the tiocmget behaviour is
> substantially changed in what it returns, in addition to the incorrect
> character being sent.
>
> Secondly, on unplugging the adaptor, a kernel OOPS is caused due to a
> null pointer dereference. See dmesg extract also attached.
>
> Following this OOPS, lsusb just hangs and is not interruptible with
> control-C, and on attempting to shut down the machine the shutdown process
> hangs when closing down Bluetooth (the built-in Bluetooth adaptor also
> presents a USB interface). Magic sysrq key still works fortunately !
>
> A different usb-serial device using the ftdi-sio driver still works
> without error.
>
> I see the following in the package changelog and wonder if this change
> is related to the destabilisation ?
>
> linux-2.6 (2.6.26-4) unstable; urgency=low
> * Add stable release 2.6.26.3:
> - usb-serial: don't release unregistered minors
The commit in question is
http://git.kernel.org/?p=linux/kernel/git/stable/linux-2.6.26.y.git;a=commit;h=bb457a9869e945299445f13bf618975d1562ab83
Please try to a kernel build with that fix reverted. If it fixes
the problem for you, please pass your debug data to Greg Kroah-Hartman
<gregkh@suse.de>, who's both one of the maintainers of the 2.6.26.x stable
releases and the Linux USB maintainer.
Cheers,
Moritz
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