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From: "Michael S. Zick" <lkml@morethan.org>
Reply-To: lkml@morethan.org
To: Roland Dreier <rdreier@cisco.com>
Subject: Re: [BUG FIX] Make x86_32 uni-processor Atomic ops, Atomic
Date: Wed, 27 May 2009 17:33:37 -0500
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Cc: peterz@infradead.org, "H. Peter Anvin" <hpa@zytor.com>,
       Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
       linux-kernel@vger.kernel.org
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On Wed May 27 2009, Roland Dreier wrote:
> 
>  > The only objective information is posted here:
>  > http://lkml.org/lkml/2009/5/20/342
> 
> Not sure if you've looked at this, but it's a lockdep trace that looks
> to be a valid lockdep report due to non-annotated code (I don't *think*
> it's a bug).  To summarize, there is the code path in
> kernel/irq/spurious.c that does:
>

I haven't looked at it - beyond my skill level.

Still trying to deal with a machine where the only symptom is a deadlock.
So I post these for someone else's eyes until I figure out the deadlock.

Mike
 
>     poll_spurious_irq_timer ->
>       poll_spurious_irqs()     [from timer, with hard IRQs on] ->
>       poll_all_shared_irqs()   [if we think an IRQ got stuck] ->
>       try_one_irq() ->
>       spin_lock(&desc->lock)   [as above -- hard IRQs on]
> 
> while kernel/irq/chip.c has:
> 
>     handle_level_irq()         [called with hard IRQs off] ->
>       spin_lock(&desc->lock)   [as above -- hard IRQs off]
> 
> and lockdep can't tell that the interrupt corresponding to desc has been
> disabled if we ever actually reach try_one_irq(), so there's no risk of
> the interrupt coming in and deadlocking while the try_one_irq() code
> holds desc->lock.
> 
> Unfortunately I don't know how to annotate this...
> 
>