linux-kernel - Re: start_kernel(): bug: interrupts were enabled early

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Message-ID: <4BB3B8FC.1020608@zytor.com>
Date:	Wed, 31 Mar 2010 14:05:00 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Matthew Wilcox <matthew@....cx>
CC:	Yinghai Lu <yinghai@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rabin Vincent <rabin@....in>,
	lkml <linux-kernel@...r.kernel.org>, penberg@...helsinki.fi,
	cl@...ux-foundation.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linux-arch@...r.kernel.org
Subject: Re: start_kernel(): bug: interrupts were enabled early

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
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