RTC: Fix early irqs caused by calling rtc_set_alarm too early

When we register an rtc device at boot, we read the alarm value
in hardware and set the rtc device's aie_timer to that value.

The initial method to do this was to simply call rtc_set_alarm()
with the value read from hardware. However, this may cause problems
as rtc_set_alarm may enable interupts, and the RTC alarm might fire,
which can cause invalid pointer dereferencing since the RTC registration
is not complete.

This patch solves the issue by initializing the rtc_device.aie_timer
y hand via rtc_initialize_alarm(). This avoids any calls to the RTC
hardware which might enable interrupts too early.

CC: Thomas Gleixner <tglx@linutronix.de>
CC: Alessandro Zummo <a.zummo@towertech.it>
Reported-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>

drivers/rtc/class.c

@@ -171,7 +171,7 @@ struct rtc_device *rtc_device_register(const char *name, struct device *dev,
 	err = __rtc_read_alarm(rtc, &alrm);
 
 	if (!err && !rtc_valid_tm(&alrm.time))
-		rtc_set_alarm(rtc, &alrm);
+		rtc_initialize_alarm(rtc, &alrm);
 
 	strlcpy(rtc->name, name, RTC_DEVICE_NAME_SIZE);
 	dev_set_name(&rtc->dev, "rtc%d", id);

drivers/rtc/interface.c

@@ -375,6 +375,32 @@ int rtc_set_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm)
 }
 EXPORT_SYMBOL_GPL(rtc_set_alarm);
 
+/* Called once per device from rtc_device_register */
+int rtc_initialize_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm)
+{
+	int err;
+
+	err = rtc_valid_tm(&alarm->time);
+	if (err != 0)
+		return err;
+
+	err = mutex_lock_interruptible(&rtc->ops_lock);
+	if (err)
+		return err;
+
+	rtc->aie_timer.node.expires = rtc_tm_to_ktime(alarm->time);
+	rtc->aie_timer.period = ktime_set(0, 0);
+	if (alarm->enabled) {
+		rtc->aie_timer.enabled = 1;
+		timerqueue_add(&rtc->timerqueue, &rtc->aie_timer.node);
+	}
+	mutex_unlock(&rtc->ops_lock);
+	return err;
+}
+EXPORT_SYMBOL_GPL(rtc_initialize_alarm);
+
+
+
 int rtc_alarm_irq_enable(struct rtc_device *rtc, unsigned int enabled)
 {
 	int err = mutex_lock_interruptible(&rtc->ops_lock);

include/linux/rtc.h

@@ -228,6 +228,8 @@ extern int rtc_read_alarm(struct rtc_device *rtc,
 			struct rtc_wkalrm *alrm);
 extern int rtc_set_alarm(struct rtc_device *rtc,
 				struct rtc_wkalrm *alrm);
+extern int rtc_initialize_alarm(struct rtc_device *rtc,
+				struct rtc_wkalrm *alrm);
 extern void rtc_update_irq(struct rtc_device *rtc,
 			unsigned long num, unsigned long events);