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Date: Wed, 31 Mar 2010 16:42:25 -0500 (CDT)
From: Christoph Lameter <cl@linux-foundation.org>
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To: Matthew Wilcox <matthew@wil.cx>
cc: "H. Peter Anvin" <hpa@zytor.com>, Yinghai Lu <yinghai@kernel.org>,
       Andrew Morton <akpm@linux-foundation.org>, Rabin Vincent <rabin@rab.in>,
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       Benjamin Herrenschmidt <benh@kernel.crashing.org>,
       linux-arch@vger.kernel.org
Subject: Re: start_kernel(): bug: interrupts were enabled early
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On Wed, 31 Mar 2010, Matthew Wilcox wrote:

> On Wed, Mar 31, 2010 at 02:05:00PM -0700, H. Peter Anvin wrote:
> > 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.
>
> It's based on down_read() and down_write() not being callable from
> interrupt context, or with interrupts disabled (since they can sleep).
> up_read(), up_write(), down_read_trylock(), down_write_trylock(),
> downgrade_write() can all be called from interrupt context since they
> cannot sleep.

Do not run the checks while we are in a single threaded context?

I thought we had some dynamic code patching thingamy that could change
those when we go to smp mode?