[PATCH 2/2] Debug handling of early spurious interrupts

[Fernando Luis Vázquez Cao]

With the advent of kdump it is possible that device drivers receive
interrupts generated in the context of a previous kernel. Ideally
quiescing the underlying devices should suffice but not all drivers do
this, either because it is not possible or because they did not
contemplate this case. Thus drivers ought to be able to handle
interrupts coming in as soon as the interrupt handler is registered.

Signed-off-by: Fernando Luis Vazquez Cao <fernando at oss.ntt.co.jp>
---

diff -urNp linux-2.6.22-orig/kernel/irq/manage.c linux-2.6.22-pendirq/kernel/irq/manage.c
--- linux-2.6.22-orig/kernel/irq/manage.c	2007-07-19 18:18:53.000000000 +0900
+++ linux-2.6.22-pendirq/kernel/irq/manage.c	2007-07-19 19:43:41.000000000 +0900
@@ -533,21 +533,32 @@ int request_irq(unsigned int irq, irq_ha
 
 	select_smp_affinity(irq);
 
-	if (irqflags & IRQF_SHARED) {
-		/*
-		 * It's a shared IRQ -- the driver ought to be prepared for it
-		 * to happen immediately, so let's make sure....
-		 * We do this before actually registering it, to make sure that
-		 * a 'real' IRQ doesn't run in parallel with our fake
-		 */
-		if (irqflags & IRQF_DISABLED) {
-			unsigned long flags;
+	/*
+	 * With the advent of kdump it possible that device drivers receive
+	 * interrupts generated in the context of a previous kernel. Ideally
+	 * quiescing the underlying devices should suffice but not all drivers
+	 * do this, either because it is not possible or because they did not
+	 * contemplate this case. Thus drivers ought to be able to handle
+	 * interrupts coming in as soon as the interrupt handler is registered.
+	 *
+	 * Besides, if it is a shared IRQ the driver ought to be prepared for
+	 * it to happen immediately too.
+	 *
+	 * We do this before actually registering it, to make sure that
+	 * a 'real' IRQ doesn't run in parallel with our fake.
+	 */
+	if (irqflags & IRQF_DISABLED) {
+		unsigned long flags;
 
-			local_irq_save(flags);
-			handler(irq, dev_id);
-			local_irq_restore(flags);
-		} else
-			handler(irq, dev_id);
+		local_irq_save(flags);
+		retval = handler(irq, dev_id);
+		local_irq_restore(flags);
+	} else
+		retval = handler(irq, dev_id);
+	if (retval == IRQ_HANDLED) {
+		printk(KERN_WARNING
+		       "%s (IRQ %d) handled a spurious interrupt\n",
+		       devname, irq);
 	}
 
 	retval = setup_irq(irq, action);