linux-kernel - Re: [BUG FIX] Make x86_32 uni-processor Atomic ops, Atomic

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Message-Id: <200905271733.42266.lkml@morethan.org>
Date:	Wed, 27 May 2009 17:33:37 -0500
From:	"Michael S. Zick" <lkml@...ethan.org>
To:	Roland Dreier <rdreier@...co.com>
Cc:	peterz@...radead.org, "H. Peter Anvin" <hpa@...or.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [BUG FIX] Make x86_32 uni-processor Atomic ops, Atomic

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...
> 
> 


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