Hi.

The history is that -mm kernels do not work for me
for a few months already. The things started from
crashing somewhere after starting init, and for the
last month - no boot at all, just
"Uncompressing... OK, booting kernel", and silence.
Early console didn't work too.
With the latest releases this degraded into an infinite
stream of the "Unknown interrupt or fault" messages.
So today my patience ran out and I started to think how
can I collect at least some info for the bug-report.
Attached is the patch that allows to gather some valueable
debug info on the problem by making an early console more
useable. I can't properly test the patch, as the kernel
still doesn't boot, so I'll explain it in details in a
hope someone else can justify the intrusive changes.


arch_hooks.h: added prototypes for setup_early_printk()
and early_printk().

head.S: added "hlt" to the dummy fault handler. This is
necessary because otherwise the fault retriggers infinitely,
causing the infinite stream of an "Unknown interrupt or fault"
messages, which scrolls away the usefull info. I don't know
if this is a safe change.

setup.c: killed wrong setup_early_printk() prototype.
Moved setup_early_printk() a bit earlier, as it was not
"early enough" to cover the bug I was fighting with.

early_printk.c: made it to start printing from the bottom
of the screen, otherwise the messages interfere with the
ones of the boot-loader, so you can't read them.

main.c: moved smp_prepare_boot_cpu() call earlier. This
was necessary because otherwise printk() can't print
It checks cpu_online(), which returns false. This change
is consistent with the UP case, where's the boot CPU is
"online" from the very beginning, AFAICS. But again, I am
not entirely sure whether this is safe.


OK, so with that patch I was hoping to collect some debug
info. It turned out though, that the main.c change also
fixes the problem itself. The lockup was happening in an
__alloc_bootmem_core(): the "if (!size)" check was succeeding,
and the BUG() was triggering. After my main.c change this no
longer happens, but I don't know where the problem was.

I still can't boot the kernel because of this
http://www.uwsg.iu.edu/hypermail/linux/kernel/0602.2/1244.html
but at least I know that with the attached patch, the boot
process goes much further.

Just in case the patch is going to be applied:
Signed-off-by: Stas Sergeev <stsp@aknet.ru>