The kernel lock is held too long while the graphics card is configured. I have seen that with some Nvidia cards, where I just have not been able to boot LOCKDEBUG kernels (example in PR 55185).
You can patch out the kernel lock spinout code (so the kernel does not limit the KERNEL_LOCK() spin time and you then can investigate other locking issues). Maybe we should offer an official option to do that? Martin P.S.: only guessing it is the graphics card, something(tm) is taking very long while holding the kernel lock, anything called during autoconfiguration could do that - but also a few other things.
