[PATCH] iio: trigger: Avoid data race

[Gyeyoung Baek <gye976@gmail.com>]

A data race could occur between `atomic_read()` and `atomic_set()`
Use `atomic_cmpxchg_relaxed()` to group them atomically.

Previously the main logic was executed when `use_count` is 0.
Now it returns early when `use_count` is not 0.

Signed-off-by: Gyeyoung Baek <gye976@gmail.com>
---
 drivers/iio/industrialio-trigger.c | 38 +++++++++++++-----------------
 1 file changed, 17 insertions(+), 21 deletions(-)

diff --git a/drivers/iio/industrialio-trigger.c b/drivers/iio/industrialio-trigger.c
index 54416a384232..33a565037e0d 100644
--- a/drivers/iio/industrialio-trigger.c
+++ b/drivers/iio/industrialio-trigger.c
@@ -194,17 +194,15 @@ static void iio_trigger_notify_done_atomic(struct iio_trigger *trig)
  */
 void iio_trigger_poll(struct iio_trigger *trig)
 {
-	int i;
-
-	if (!atomic_read(&trig->use_count)) {
-		atomic_set(&trig->use_count, CONFIG_IIO_CONSUMERS_PER_TRIGGER);
-
-		for (i = 0; i < CONFIG_IIO_CONSUMERS_PER_TRIGGER; i++) {
-			if (trig->subirqs[i].enabled)
-				generic_handle_irq(trig->subirq_base + i);
-			else
-				iio_trigger_notify_done_atomic(trig);
-		}
+	if (atomic_cmpxchg_relaxed(&trig->use_count, 0,
+				   CONFIG_IIO_CONSUMERS_PER_TRIGGER))
+		return;
+
+	for (int i = 0; i < CONFIG_IIO_CONSUMERS_PER_TRIGGER; i++) {
+		if (trig->subirqs[i].enabled)
+			generic_handle_irq(trig->subirq_base + i);
+		else
+			iio_trigger_notify_done_atomic(trig);
 	}
 }
 EXPORT_SYMBOL(iio_trigger_poll);
@@ -225,17 +223,15 @@ EXPORT_SYMBOL(iio_trigger_generic_data_rdy_poll);
  */
 void iio_trigger_poll_nested(struct iio_trigger *trig)
 {
-	int i;
-
-	if (!atomic_read(&trig->use_count)) {
-		atomic_set(&trig->use_count, CONFIG_IIO_CONSUMERS_PER_TRIGGER);
+	if (atomic_cmpxchg_relaxed(&trig->use_count, 0,
+				   CONFIG_IIO_CONSUMERS_PER_TRIGGER))
+		return;
 
-		for (i = 0; i < CONFIG_IIO_CONSUMERS_PER_TRIGGER; i++) {
-			if (trig->subirqs[i].enabled)
-				handle_nested_irq(trig->subirq_base + i);
-			else
-				iio_trigger_notify_done(trig);
-		}
+	for (int i = 0; i < CONFIG_IIO_CONSUMERS_PER_TRIGGER; i++) {
+		if (trig->subirqs[i].enabled)
+			handle_nested_irq(trig->subirq_base + i);
+		else
+			iio_trigger_notify_done(trig);
 	}
 }
 EXPORT_SYMBOL(iio_trigger_poll_nested);
-- 
2.43.0