From: Pavel Emelianov Date: Fri, 10 Nov 2006 20:27:56 +0000 (-0800) Subject: [PATCH] Fix misrouted interrupts deadlocks X-Git-Tag: v2.6.19-rc6~35 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f72fa707604c015a6625e80f269506032d5430dc;p=linux-2.6 [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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/kernel/irq/spurious.c b/kernel/irq/spurious.c index 543ea2e5ad..9c7e2e4c1f 100644 --- a/kernel/irq/spurious.c +++ b/kernel/irq/spurious.c @@ -147,7 +147,11 @@ void note_interrupt(unsigned int irq, struct irq_desc *desc, if (unlikely(irqfixup)) { /* Don't punish working computers */ if ((irqfixup == 2 && irq == 0) || action_ret == IRQ_NONE) { - int ok = misrouted_irq(irq); + int ok; + + spin_unlock(&desc->lock); + ok = misrouted_irq(irq); + spin_lock(&desc->lock); if (action_ret == IRQ_NONE) desc->irqs_unhandled -= ok; }