Subject: Re: [BUG] 2.6.25-rc3-mm1 kernel panic while bootup on powerpc ()
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reply-To: benh@kernel.crashing.org
To: Andrew Morton <akpm@linux-foundation.org>
Cc: mikey@neuling.org, kamalesh@linux.vnet.ibm.com, linuxppc-dev@ozlabs.org,
       linux-kernel@vger.kernel.org, willy@debian.org
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Date: Thu, 06 Mar 2008 11:52:42 +1100
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On Wed, 2008-03-05 at 16:44 -0800, Andrew Morton wrote:
> On Thu, 06 Mar 2008 11:03:31 +1100
> Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:
> 
> > 
> > > Yes, we are - it's the semaphore rewrite which is doing this in
> > > start_kernel().  It's being discussed.
> > > 
> > > Enabling interrupts too early on powerpc was discovered to be fatal on
> > > powerpc years ago.  It looks like that remains the case.
> > 
> > Regarding these issues. I could make it non fatal and just WARN_ON,
> > provided that I have a way to differentiate legal vs. illegal calls
> > to local_irq_enable().
> 
> And local_irq_restore() and various other things.

Yes, on powerpc 64 bits, they all go down to one C function that does
the lazy enable/disable, so it would be easy to deal with. 32 bits
doesn't have it that simple tho.

> I'd have thought that the way to do this would be to add it to lockdep -
> lockdep already has all the infrastructure and code sites to do this.
> 
> Set some special flag saying its-ok-to-enable-interrupts-now and test that
> in lockdep.

Ok.

> akpm:/usr/src/25> grep LOCKDEP arch/powerpc/Kconfig 
> akpm:/usr/src/25> 
> 
> losers ;)

I have lockdep patches for powerpc 32 and 64 bits. They aren't upstream
yet as they need a bit more beating up and there's at least one machine
that doesn't seem to like them, so I'm working on just that. That's a
good idea to add the test to lockdep tho, I'll see what I can do.

> Still, doing it for
> 
> akpm:/usr/src/25> grep -l LOCKDEP arch/*/Kconfig 
> arch/arm/Kconfig
> arch/avr32/Kconfig
> arch/mips/Kconfig
> arch/s390/Kconfig
> arch/sh/Kconfig
> arch/sparc64/Kconfig
> arch/um/Kconfig
> arch/x86/Kconfig
> 
> should give pretty good coverage.

Ben.


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