[PATCH v4 2/3] iio: accel: bmc150: take the lock before checking ev_enable_state

[Gabriel Rondon <grondon@gmail.com>]

bmc150_accel_write_event_config() compared the requested state against
data->ev_enable_state before acquiring data->mutex. Two threads racing
to enable and disable the same event can both pass the check and then
both call bmc150_accel_set_interrupt(), which tracks enables with an
atomic users count. The inc/dec can become unbalanced, leaving the
interrupt enabled or disabled against the callers' intent.

Move the check inside the locked region so the test of ev_enable_state
and its update are atomic with respect to the interrupt accounting.

Fixes: 14ee64f438b8 ("iio: bmc150: exit early if event / trigger state is not changed")
Cc: stable@vger.kernel.org
Signed-off-by: Gabriel Rondon <grondon@gmail.com>
---
 drivers/iio/accel/bmc150-accel-core.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/accel/bmc150-accel-core.c b/drivers/iio/accel/bmc150-accel-core.c
index d067da9b5ce4..bcbb9f0c830a 100644
--- a/drivers/iio/accel/bmc150-accel-core.c
+++ b/drivers/iio/accel/bmc150-accel-core.c
@@ -805,11 +805,13 @@ static int bmc150_accel_write_event_config(struct iio_dev *indio_dev,
 	struct bmc150_accel_data *data = iio_priv(indio_dev);
 	int ret;
 
-	if (state == data->ev_enable_state)
-		return 0;
-
 	mutex_lock(&data->mutex);
 
+	if (state == data->ev_enable_state) {
+		mutex_unlock(&data->mutex);
+		return 0;
+	}
+
 	ret = bmc150_accel_set_interrupt(data, BMC150_ACCEL_INT_ANY_MOTION,
 					 state);
 	if (ret < 0) {
-- 
2.50.1 (Apple Git-155)