[PATCH v2] clockevents/drivers/cs5535: improve resilience to spurious interrupts

[David Kozub <zub@linux.fjfi.cvut.cz>]

The interrupt handler mfgpt_tick() is not robust versus spurious
interrupts which happen before the clock event device is registered and
fully initialized.

The reason is that the safe guard against spurious interrupts solely
checks for the clockevents shutdown state, but lacks a check for
detached state. If the interrupt hits while the device is in detached
state it passes the safe guard and dereferences the event handler call
back which is NULL.

Add the missing state check.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: David Kozub <zub@linux.fjfi.cvut.cz>
---
Changes in v2:
  - Use commit message suggested by Thomas Gleixner
  - Fix formatting of multi-line if condition

 drivers/clocksource/cs5535-clockevt.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/clocksource/cs5535-clockevt.c b/drivers/clocksource/cs5535-clockevt.c
index a1df588343f2..1de8cac99a0e 100644
--- a/drivers/clocksource/cs5535-clockevt.c
+++ b/drivers/clocksource/cs5535-clockevt.c
@@ -117,7 +117,8 @@ static irqreturn_t mfgpt_tick(int irq, void *dev_id)
 	/* Turn off the clock (and clear the event) */
 	disable_timer(cs5535_event_clock);
 
-	if (clockevent_state_shutdown(&cs5535_clockevent))
+	if (clockevent_state_detached(&cs5535_clockevent) ||
+	    clockevent_state_shutdown(&cs5535_clockevent))
 		return IRQ_HANDLED;
 
 	/* Clear the counter */
-- 
2.14.2