powerpc/64: fix irq replay missing preempt

Prior to commit 3282a3da25 ("powerpc/64: Implement soft interrupt
replay in C"), replayed interrupts returned by the regular interrupt
exit code, which performs preemption in case an interrupt had set
need_resched.

This logic was missed by the conversion. Adding preempt_disable/enable
around the interrupt replay and final irq enable will reschedule if
needed.

Fixes: 3282a3da25 ("powerpc/64: Implement soft interrupt replay in C")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200915114650.3980244-1-npiggin@gmail.com

arch/powerpc/kernel/irq.c

@@ -368,6 +368,12 @@ notrace void arch_local_irq_restore(unsigned long mask)
 		}
 	}
 
+	/*
+	 * Disable preempt here, so that the below preempt_enable will
+	 * perform resched if required (a replayed interrupt may set
+	 * need_resched).
+	 */
+	preempt_disable();
 	irq_soft_mask_set(IRQS_ALL_DISABLED);
 	trace_hardirqs_off();
 
@@ -377,6 +383,7 @@ notrace void arch_local_irq_restore(unsigned long mask)
 	trace_hardirqs_on();
 	irq_soft_mask_set(IRQS_ENABLED);
 	__hard_irq_enable();
+	preempt_enable();
 }
 EXPORT_SYMBOL(arch_local_irq_restore);