[PATCH] genirq: do not mask interrupts by default

Never mask interrupts immediately upon request.  Disabling interrupts in
high-performance codepaths is rare, and on the other hand this change could
recover lost edges (or even other types of lost interrupts) by conservatively
only masking interrupts after they happen.  (NOTE: with this change the
highlevel irq-disable code still soft-disables this IRQ line - and if such an
interrupt happens then the IRQ flow handler keeps the IRQ masked.)

Mark i8529A controllers as 'never loses an edge'.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/i386/kernel/i8259.c

@@ -41,6 +41,7 @@ static void mask_and_ack_8259A(unsigned int);
 static struct irq_chip i8259A_chip = {
 	.name		= "XT-PIC",
 	.mask		= disable_8259A_irq,
+	.disable	= disable_8259A_irq,
 	.unmask		= enable_8259A_irq,
 	.mask_ack	= mask_and_ack_8259A,
 };

arch/x86_64/kernel/i8259.c

@@ -103,6 +103,7 @@ static void mask_and_ack_8259A(unsigned int);
 static struct irq_chip i8259A_chip = {
 	.name		= "XT-PIC",
 	.mask		= disable_8259A_irq,
+	.disable	= disable_8259A_irq,
 	.unmask		= enable_8259A_irq,
 	.mask_ack	= mask_and_ack_8259A,
 };

kernel/irq/chip.c

@@ -230,10 +230,6 @@ static void default_enable(unsigned int irq)
  */
 static void default_disable(unsigned int irq)
 {
-	struct irq_desc *desc = irq_desc + irq;
-
-	if (!(desc->status & IRQ_DELAYED_DISABLE))
-		desc->chip->mask(irq);
 }
 
 /*
@@ -298,13 +294,18 @@ handle_simple_irq(unsigned int irq, struct irq_desc *desc)
 
 	if (unlikely(desc->status & IRQ_INPROGRESS))
 		goto out_unlock;
-	desc->status &= ~(IRQ_REPLAY | IRQ_WAITING);
 	kstat_cpu(cpu).irqs[irq]++;
 
 	action = desc->action;
-	if (unlikely(!action || (desc->status & IRQ_DISABLED)))
+	if (unlikely(!action || (desc->status & IRQ_DISABLED))) {
+		if (desc->chip->mask)
+			desc->chip->mask(irq);
+		desc->status &= ~(IRQ_REPLAY | IRQ_WAITING);
+		desc->status |= IRQ_PENDING;
 		goto out_unlock;
+	}
 
+	desc->status &= ~(IRQ_REPLAY | IRQ_WAITING | IRQ_PENDING);
 	desc->status |= IRQ_INPROGRESS;
 	spin_unlock(&desc->lock);
 
@@ -396,11 +397,13 @@ handle_fasteoi_irq(unsigned int irq, struct irq_desc *desc)
 
 	/*
 	 * If its disabled or no action available
-	 * keep it masked and get out of here
+	 * then mask it and get out of here:
 	 */
 	action = desc->action;
 	if (unlikely(!action || (desc->status & IRQ_DISABLED))) {
 		desc->status |= IRQ_PENDING;
+		if (desc->chip->mask)
+			desc->chip->mask(irq);
 		goto out;
 	}