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

From: Roland Dreier
Date: Wed May 27 2009 - 18:13:29 EST

> 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:

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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