clockevents/drivers/cs5535: Improve resilience to spurious interrupts

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.

Fixes: 8f9327cbb6e8 ("clockevents/drivers/cs5535: Migrate to new 'set-state' interface")
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: David Kozub <zub@linux.fjfi.cvut.cz>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20171020093103.3317F6004D@linux.fjfi.cvut.cz

diff --git a/drivers/clocksource/cs5535-clockevt.c b/drivers/clocksource/cs5535-clockevt.c
index a1df588343f2dac1fb1c6acb8f579f3688ad6938..1de8cac99a0e93b21d38f5c23f29739ec06caab7 100644 (file)
--- 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 */