David C. Hansen wrote:
> Adam J. Richter wrote:
>> The was a small change to to kernel/exit.c
>> in 2.5.8-pre1 which deleted a kernel_lock() call.  Restoring that line
>> resulted in a kernel that booted fine.
>>
> I take it you don't have a copy of the BUG().   I was going to ask if 
> preemption was enabled, but I see that it was from another message.  I 
> was guessing that preemption contributed to this, but now I know.  The 
> lock_kernel() has 2 different effects here.  It locks the kernel_flag, 
> AND it disables preemption.  The correct fix here will probably be to 
> disable preemption, rather than readd the lock_kernel(). 

I've replicated the problem too.
I've diabled preemption in the area where it used to be disabled because 
of the old lock_kernel().  I'm sending this message from a machine with 
that patch applied, so the patch does fix it.  As the comment says, this 
is something that the preempt experts need to take a look at.
Linus, this is a hack, and there is probably still a window where 
preemption can happen.  But, it is a band-aid until we find the real 
problem.


-- 
Dave Hansen
haveblue@us.ibm.com