[issue174] Unloading md module causes a panic

[Nicolas Thery]

2009/1/22 Antonio Huete Jimenez (via DragonFly issue tracker)
<sinknull at crater.dragonflybsd.org>:
>
> Antonio Huete Jimenez <tuxillo at quantumachine.net> added the comment:
>
> Still happening on 2.0.1
> See attached image.

I can reproduce it if and only if md is already compiled in the kernel.

What happens is that when kldloading md, the kernel tries to register
the debug.mddebug sysctl a second time (as md is already in the
kernel).  It complains (the "can't re-use a leaf" msg) and stops the
registration but carries on loading the module.

When kldunloading, the kernel tries to unregister the module instance
of debug.mddebug and panics because it was not registered in the first
place.

Is there a way to detect during kldload that the module is already
part of the kernel?

I propose to close this bug as it is caused by incorrect user manipulation.