ath9k: avoid potential freezing during random generator read

In the worst case, ath9k_rng_stop() may take 10s to stop rng kthread.
The time is too long for users, use wait_event_interruptible_timeout()
instead of msleep_interruptible(), wakup immediately once
kthread_should_stop() is true.
Signed-off-by: Miaoqing Pan <miaoqing@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

drivers/net/wireless/ath/ath9k/rng.c

@@ -24,6 +24,8 @@
 #define ATH9K_RNG_BUF_SIZE	320
 #define ATH9K_RNG_ENTROPY(x)	(((x) * 8 * 10) >> 5) /* quality: 10/32 */
 
+static DECLARE_WAIT_QUEUE_HEAD(rng_queue);
+
 static int ath9k_rng_data_read(struct ath_softc *sc, u32 *buf, u32 buf_size)
 {
 	int i, j;
@@ -85,7 +87,9 @@ static int ath9k_rng_kthread(void *data)
 						 ATH9K_RNG_BUF_SIZE);
 		if (unlikely(!bytes_read)) {
 			delay = ath9k_rng_delay_get(++fail_stats);
-			msleep_interruptible(delay);
+			wait_event_interruptible_timeout(rng_queue,
+							 kthread_should_stop(),
+							 msecs_to_jiffies(delay));
 			continue;
 		}