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

From: Michael S. Zick
Date: Wed May 27 2009 - 18:33:53 EST

On Wed May 27 2009, Roland Dreier wrote:
> > The only objective information is posted here:
> >
> 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.


> 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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