Date: Wed, 31 May 2006 08:31:03 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Andrew Morton <akpm@osdl.org>
Cc: Steven Rostedt <rostedt@goodmis.org>, linux-kernel@vger.kernel.org
Subject: Re: 2.6.17-rc5-mm1
Message-ID: <20060531063103.GC21779@elte.hu>
References: <20060530022925.8a67b613.akpm@osdl.org> <1149045448.28264.4.camel@localhost.localdomain> <20060530211442.a260a32e.akpm@osdl.org>
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* Andrew Morton <akpm@osdl.org> wrote:

> Without having looked at it very hard, I'd venture that this is a 
> false positive - that driver uses disable_irq() to prevent reentry 
> onto that lock.

correct.

> It does that because it knows it's about to spend a long time talking 
> with the mii registers and it doesn't want to do that with interrupts 
> disabled.

i still consider it a 'quirky' locking construct, because disabling 
interrupts for a long time also disables all other devices sharing the 
same IRQ line - not nice.

Also, this is a really hard case for lockdep to detect automatically. 
(fortunately it's also relatively rare)

OTOH, the straightforward lockdep workaround would be to take the 
spinlock and thus disable all local interrupts - not too nice either. 

Albeit in some ways it's still a bit nicer conceptually than disabling 
the irq line, because other CPUs are still operational, and under 
certain locking designs [preempt-rt] spin_lock_irq() does not disable 
local interrupts.
 
Steve, can you think of any better solution? I dont have this card.

	Ingo
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