[PATCH] Fix misrouted interrupts deadlocks
authorPavel Emelianov <xemul@openvz.org>
Fri, 10 Nov 2006 20:27:56 +0000 (12:27 -0800)
committerLinus Torvalds <torvalds@g5.osdl.org>
Mon, 13 Nov 2006 15:40:43 +0000 (07:40 -0800)
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>
kernel/irq/spurious.c

index 543ea2e5ad9301944ab520303bd7fe84e4e92f88..9c7e2e4c1fe717ef0f309eed0163a2d28a6cd5a7 100644 (file)
@@ -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;
                }