linux-kernel - Re: [PATCH] lockdep: annotate i386 apm

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Date:	Thu, 12 Oct 2006 10:02:12 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...l.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel <linux-kernel@...r.kernel.org>, sfr@...b.auug.org.au
Subject: Re: [PATCH] lockdep: annotate i386 apm


* Andrew Morton <akpm@...l.org> wrote:

> > So, say interrupts were enabled when entering apm_bios_call*(); you now
> > save that in flags, disable interrupts, and enable them again.
> > Upon reaching local_irq_restore(), we'll hit the else branch with irq's
> > enabled and call trace_hardirqs_on(), which goes EEEK!
> 
> I'd assumed lockdep was less stupid than that ;) This?  Seems a bit 
> overdone..

the problem is not lockdep but that the BIOS enables IRQs behind the 
back of the kernel. Lockdep needs to be taught about that - if this 
happens unconditionally then i'd suggest to insert an unconditional 
trace_hardirqs_on() call to after the local_irq_save() that we do prior 
calling the BIOS. (that will be a NOP if lockdep is not enabled)

	Ingo
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