How to debug DEBUG_TEST_DRIVER_REMOVE hang during loading of kernel?

[Maarten Maathuis]

Hi,

I recently had trouble with loading a 4.9rcX kernel, which was hanging
after loading the initial kernel ramdisk. After some painful bisecting
I found this:

bea5b158ff0da9c7246ff391f754f5f38e34577a is the first bad commit
commit bea5b158ff0da9c7246ff391f754f5f38e34577a
Author: Rob Herring <robh@xxxxxxxxxx>
Date:   Thu Aug 11 10:20:58 2016 -0500

    driver core: add test of driver remove calls during probe

    In recent discussions on ksummit-discuss[1], it was suggested to do a
    sequence of probe, remove, probe for testing driver remove paths. This
    adds a kconfig option for said test.

    [1] https://lists.linuxfoundation.org/pipermail/ksummit-discuss/2016-August/003459.html

    Suggested-by: Arnd Bergmann <arnd@xxxxxxxx>
    Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Rob Herring <robh@xxxxxxxxxx>
    Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

It turns out that the package i was using to build the kernel had
DEBUG_TEST_DRIVER_REMOVE enabled.

How do I actually figure out why this test causes a hang. I don't have
a COM port available to use as serial console, and i don't know if it
would even help.

Please CC me as i'm not a member of this mailinglist.

Maarten.

-- 
Far away from the primal instinct, the song seems to fade away, the
river get wider between your thoughts and the things we do and say.