powerpc: powernv: Annotate data races in opal events

The kopald thread handles opal events as they appear, but by polling a
static bit-vector in last_outstanding_events. Annotate these data races
accordingly. We are not at risk of missing events, but use of READ_ONCE,
WRITE_ONCE will assist readers in seeing that kopald only consumes the
events it is aware of when it is scheduled. Also removes extraneous
KCSAN warnings.

Signed-off-by: Rohan McLure <[email protected]>
Reviewed-by: Nicholas Piggin <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
Link: https://msgid.link/[email protected]

Author: rohanmclure

arch/powerpc/platforms/powernv/opal-irqchip.c

@@ -59,7 +59,7 @@ void opal_handle_events(void)
 
 		cond_resched();
 	}
-	last_outstanding_events = 0;
+	WRITE_ONCE(last_outstanding_events, 0);
 	if (opal_poll_events(&events) != OPAL_SUCCESS)
 		return;
 	e = be64_to_cpu(events) & opal_event_irqchip.mask;
@@ -69,7 +69,7 @@ void opal_handle_events(void)
 
 bool opal_have_pending_events(void)
 {
-	if (last_outstanding_events & opal_event_irqchip.mask)
+	if (READ_ONCE(last_outstanding_events) & opal_event_irqchip.mask)
 		return true;
 	return false;
 }
@@ -124,7 +124,7 @@ static irqreturn_t opal_interrupt(int irq, void *data)
 	__be64 events;
 
 	opal_handle_interrupt(virq_to_hw(irq), &events);
-	last_outstanding_events = be64_to_cpu(events);
+	WRITE_ONCE(last_outstanding_events, be64_to_cpu(events));
 	if (opal_have_pending_events())
 		opal_wake_poller();