drivers: modem: Fix possible race condition, reset sem before data send

Fix possible race condition, reset the response semaphore before we send
any data. In case we don't get scheduled back before the response is
processed.

Signed-off-by: Joakim Andersson <[email protected]>

Author: joerchan

drivers/modem/ublox-sara-r4.c

@@ -486,11 +486,16 @@ static ssize_t send_cert(struct modem_socket *sock,
 		goto exit;
 	}
 
+	/* Reset response semaphore before sending data
+	 * So that we are sure that we won't use a previously pending one
+	 * And we won't miss the one that is going to be freed
+	 */
+	k_sem_reset(&mdata.sem_response);
+
 	/* slight pause per spec so that @ prompt is received */
 	k_sleep(MDM_PROMPT_CMD_DELAY);
 	mctx.iface.write(&mctx.iface, cert_data, cert_len);
 
-	k_sem_reset(&mdata.sem_response);
 	ret = k_sem_take(&mdata.sem_response, K_MSEC(1000));
 
 	if (ret == 0) {