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

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Message-ID: <alpine.DEB.2.00.1003311640410.30456@router.home>
Date:	Wed, 31 Mar 2010 16:42:25 -0500 (CDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Matthew Wilcox <matthew@....cx>
cc:	"H. Peter Anvin" <hpa@...or.com>, Yinghai Lu <yinghai@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rabin Vincent <rabin@....in>,
	lkml <linux-kernel@...r.kernel.org>, penberg@...helsinki.fi,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linux-arch@...r.kernel.org
Subject: Re: start_kernel(): bug: interrupts were enabled early

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?

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