powerpc/irq: Fix bug with new lazy IRQ handling code

We had a case where we could turn on hard interrupts while
leaving the PACA_IRQ_HARD_DIS bit set in the PACA. This can
in turn cause a BUG_ON() to hit in __check_irq_replay() due
to interrupt state getting out of sync.

The assembly code was also way too convoluted. Instead, we
now leave it to the C code to do the right thing which ends
up being smaller and more readable.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index 43eb74f..c6c6f3b 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -260,11 +260,17 @@
  * if they are currently disabled. This is typically called before
  * schedule() or do_signal() when returning to userspace. We do it
  * in C to avoid the burden of dealing with lockdep etc...
+ *
+ * NOTE: This is called with interrupts hard disabled but not marked
+ * as such in paca->irq_happened, so we need to resync this.
  */
 void restore_interrupts(void)
 {
-	if (irqs_disabled())
+	if (irqs_disabled()) {
+		local_paca->irq_happened |= PACA_IRQ_HARD_DIS;
 		local_irq_enable();
+	} else
+		__hard_irq_enable();
 }
 
 #endif /* CONFIG_PPC64 */