[PATCH v1] iio: trigger: warn about non-registered iio trigger getting attempt

[Dmitry Rokosov <DDRokosov@sberdevices.ru>]

As a part of patch series about wrong trigger register() and get()
calls order in the some IIO drivers trigger initialization path:

https://lore.kernel.org/all/20220524181150.9240-1-ddrokosov@sberdevices.ru/

runtime WARN() is added to alarm IIO driver authors who make such
a mistake.

When IIO driver allocates a new IIO trigger, it should register it before
calling get() operation. Otherwise, the next iio_trigger_put() will upset
refcnt balance.

Signed-off-by: Dmitry Rokosov <ddrokosov@sberdevices.ru>
---
 include/linux/iio/trigger.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/include/linux/iio/trigger.h b/include/linux/iio/trigger.h
index 4c69b144677b..4a008b952710 100644
--- a/include/linux/iio/trigger.h
+++ b/include/linux/iio/trigger.h
@@ -93,6 +93,15 @@ static inline void iio_trigger_put(struct iio_trigger *trig)
 static inline struct iio_trigger *iio_trigger_get(struct iio_trigger *trig)
 {
 	get_device(&trig->dev);
+
+	/*
+	 * If driver hasn't called iio_trigger_register() before and trig->owner
+	 * wasn't initialized properly, trigger will have wrong number of users
+	 */
+	WARN(!trig->owner,
+	     "Ignore module getting for non-registered iio trigger %s\n",
+	     trig->name);
+
 	__module_get(trig->owner);
 
 	return trig;
-- 
2.36.0