[media] exynos4-is: Add locking at fimc(-lite) subdev unregistered handler

Protect the fimc/fimc-lite video nodes unregistration with their video
lock. This prevents a kernel crash when e.g. udev opens a video node
right after the driver registers it and then the driver tries to
unregister it and defers its probing. Using video_is_unregistered()
together with the video mutex allows safe unregistration of the video
nodes at any time.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/platform/exynos4-is/fimc-capture.c

@@ -1855,6 +1855,8 @@ static void fimc_capture_subdev_unregistered(struct v4l2_subdev *sd)
 	if (fimc == NULL)
 		return;
 
+	mutex_lock(&fimc->lock);
+
 	fimc_unregister_m2m_device(fimc);
 	vdev = &fimc->vid_cap.ve.vdev;
 
@@ -1866,6 +1868,8 @@ static void fimc_capture_subdev_unregistered(struct v4l2_subdev *sd)
 	}
 	kfree(fimc->vid_cap.ctx);
 	fimc->vid_cap.ctx = NULL;
+
+	mutex_unlock(&fimc->lock);
 }
 
 static const struct v4l2_subdev_internal_ops fimc_capture_sd_internal_ops = {

drivers/media/platform/exynos4-is/fimc-lite.c

@@ -1300,11 +1300,15 @@ static void fimc_lite_subdev_unregistered(struct v4l2_subdev *sd)
 	if (fimc == NULL)
 		return;
 
+	mutex_lock(&fimc->lock);
+
 	if (video_is_registered(&fimc->ve.vdev)) {
 		video_unregister_device(&fimc->ve.vdev);
 		media_entity_cleanup(&fimc->ve.vdev.entity);
 		fimc->ve.pipe = NULL;
 	}
+
+	mutex_unlock(&fimc->lock);
 }
 
 static const struct v4l2_subdev_internal_ops fimc_lite_subdev_internal_ops = {