linux-kernel - Re: crash by cdc_acm driver in kernels 4.8-rc1/5

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Date:   Wed, 28 Sep 2016 16:46:57 +0200
From:   Wim Osterholt <wim@....tudelft.nl>
To:     Oliver Neukum <oneukum@...e.com>
Cc:     linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        Wim Osterholt <wim@....tudelft.nl>
Subject: Re: crash by cdc_acm driver in kernels 4.8-rc1/5

On Wed, Sep 28, 2016 at 11:16:04AM +0200, Oliver Neukum wrote:
> 
> Very good. This is a valid oops. We can do two things. When I
> decode it, seems to crash in acm_alloc_minor() which does not make
> sense. It is likely that our kernels or compilers are a bit different.
> Could you please call gdb on your kernel module cdc-acm.ko
> and do:
> 
> list *(acm_probe+0x4ee)
> 
> this should show you where it crashes.

Currently gcc-4.9.3-rc3.
This is from vanilla kernel 4.8-rc8

# gdb ./cdc-acm.ko
GNU gdb (Gentoo 7.10.1 vanilla) 7.10.1
Copyright (C) 2015 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "i686-pc-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see: <https://bugs.gentoo.org/>.
Find the GDB manual and other documentation resources online at: <http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./cdc-acm.ko...done.
(gdb) list *(acm_probe+0x4ee)
0x1c9b is in acm_probe (drivers/usb/class/cdc-acm.c:1346).
1341            acm->control = control_interface;
1342            acm->data = data_interface;
1343            acm->minor = minor;
1344            acm->dev = usb_dev;
1345            if (h.usb_cdc_acm_descriptor)
1346                    acm->ctrl_caps = h.usb_cdc_acm_descriptor->bmCapabilities;
1347            if (quirks & NO_CAP_LINE)
1348                    acm->ctrl_caps &= ~USB_CDC_CAP_LINE;
1349            acm->ctrlsize = ctrlsize;
1350            acm->readsize = readsize;
(gdb) quit

A new kernel is compiling now.

Regards, Wim.