Re: start_kernel(): bug: interrupts were enabled early

H. Peter Anvin
2010-03-31T21:10:10Z

On 03/31/2010 02:01 PM, Matthew Wilcox wrote:
> On Wed, Mar 31, 2010 at 01:47:23PM -0700, Yinghai Lu wrote:
>>>>> This appears to be caused by:
>>>>>
>>>>> start_kernel -> radix_tree_init -> kmem_cache_create (slub) ->
>>>>> down_write -> __down_write (lib/rwsem-spinlock.c) -> spin_unlock_irq
>>>>>
>>> That's going to be hard to fix.
>>>
>> spin_unlock_irq from arm is different from other archs?
>
> Not all arches use lib/rwsem-spinlock.c. In particular, x86 doesn't
> when X86_XADD is set.
>

What I note is that lib/rwsem-spinlock.c seems to be rather inconsistent
in its use of spin_lock_irqsave/spin_lock_irqrestore versus
spin_lock_irq/spin_unlock_irq... in fact, __down_read is the *only*
place where we use the latter as opposed to the former.

Is that a bug? If so, it would certainly explain this behavior.

-hpa