[PATCH] Fix misrouted interrupts deadlocks
While testing kernel on machine with "irqpoll" option I've caught such a lockup: __do_IRQ() spin_lock(&desc->lock); desc->chip->ack(); /* IRQ is ACKed */ note_interrupt() misrouted_irq() handle_IRQ_event() if (...) local_irq_enable_in_hardirq(); /* interrupts are enabled from now */ ... __do_IRQ() /* same IRQ we've started from */ spin_lock(&desc->lock); /* LOCKUP */ Looking at misrouted_irq() code I've found that a potential deadlock like this can also take place: 1CPU: __do_IRQ() spin_lock(&desc->lock); /* irq = A */ misrouted_irq() for (i = 1; i < NR_IRQS; i++) { spin_lock(&desc->lock); /* irq = B */ if (desc->status & IRQ_INPROGRESS) { 2CPU: __do_IRQ() spin_lock(&desc->lock); /* irq = B */ misrouted_irq() for (i = 1; i < NR_IRQS; i++) { spin_lock(&desc->lock); /* irq = A */ if (desc->status & IRQ_INPROGRESS) { As the second lock on both CPUs is taken before checking that this irq is being handled in another processor this may cause a deadlock. This issue is only theoretical. I propose the attached patch to fix booth problems: when trying to handle misrouted IRQ active desc->lock may be unlocked. Acked-by: Ingo Molnar <mingo@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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@ -147,7 +147,11 @@ void note_interrupt(unsigned int irq, struct irq_desc *desc,
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if (unlikely(irqfixup)) {
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/* Don't punish working computers */
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if ((irqfixup == 2 && irq == 0) || action_ret == IRQ_NONE) {
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int ok = misrouted_irq(irq);
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int ok;
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spin_unlock(&desc->lock);
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ok = misrouted_irq(irq);
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spin_lock(&desc->lock);
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if (action_ret == IRQ_NONE)
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desc->irqs_unhandled -= ok;
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}
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