[PATCH 4.4 66/79] iio: light: opt3001: fix mutex unlock race

[Greg Kroah-Hartman]

From: David Frey <dpfrey@xxxxxxxxx>

commit 82f3015635249a8c8c45bac303fd84905066f04f upstream.

When an end-of-conversion interrupt is received after performing a
single-shot reading of the light sensor, the driver was waking up the
result ready queue before checking opt->ok_to_ignore_lock to determine
if it should unlock the mutex. The problem occurred in the case where
the other thread woke up and changed the value of opt->ok_to_ignore_lock
to false prior to the interrupt thread performing its read of the
variable. In this case, the mutex would be unlocked twice.

Signed-off-by: David Frey <dpfrey@xxxxxxxxx>
Reviewed-by: Andreas Dannenberg <dannenberg@xxxxxx>
Fixes: 94a9b7b1809f ("iio: light: add support for TI's opt3001 light sensor")
Cc: <Stable@xxxxxxxxxxxxxxx>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/iio/light/opt3001.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/drivers/iio/light/opt3001.c
+++ b/drivers/iio/light/opt3001.c
@@ -646,6 +646,7 @@ static irqreturn_t opt3001_irq(int irq,
 	struct iio_dev *iio = _iio;
 	struct opt3001 *opt = iio_priv(iio);
 	int ret;
+	bool wake_result_ready_queue = false;
 
 	if (!opt->ok_to_ignore_lock)
 		mutex_lock(&opt->lock);
@@ -680,13 +681,16 @@ static irqreturn_t opt3001_irq(int irq,
 		}
 		opt->result = ret;
 		opt->result_ready = true;
-		wake_up(&opt->result_ready_queue);
+		wake_result_ready_queue = true;
 	}
 
 out:
 	if (!opt->ok_to_ignore_lock)
 		mutex_unlock(&opt->lock);
 
+	if (wake_result_ready_queue)
+		wake_up(&opt->result_ready_queue);
+
 	return IRQ_HANDLED;
 }