Commit 78eef01b0fae087c5fadbd85dd4fe2918c3a015f (on_each_cpu(): disable local interrupts) Breaks SGI IP32

[Kumba <kumba@gentoo.org>]

Finally managed to track down the git commit causing SGI IP32 (O2) systems to 
lock up really early in the boot cycle, but I'm at a loss to understand why.

Effect:
It appears the system silently hangs somewhere in the void between function 
calls when trying to invoke the memset() call in __alloc_bootmem_core() in 
mm/bootmem.c.  This puts the machine hardware in a state such that a simple soft 
reset doesn't clear it -- the machine has to be cold booted to get it to boot a 
working kernel again.

Determined Cause:
It seems this commit:
78eef01b0fae087c5fadbd85dd4fe2918c3a015f
	[PATCH] on_each_cpu(): disable local interrupts

Is the cause.  I've verified this by reversing this one change on a 2.6.17-rc4 
tree, and it'll boot to a mini-userland (initramfs-based) and appears to 
function normally.


But this is as far as I can trace this.  I'm not sure what this change is doing 
internally that's triggering this lockup on O2 systems.  It doesn't appear to 
affect Octane (IP30) systems or Origin (IP27).  I haven't test-ran it on 
IP22/IP28 hardware yet, so only IP32 is known to be affected.  Unsure about 
non-SGI MIPS hardware.

Thoughts?


--Kumba

-- 
Gentoo/MIPS Team Lead
Gentoo Foundation Board of Trustees

"Such is oft the course of deeds that move the wheels of the world: small hands 
do them because they must, while the eyes of the great are elsewhere."  --Elrond