[PATCHv4 1/6] media: core: v4l2-async.c: unreg subdev if asc_list is, empty

[Hans Verkuil <hverkuil+cisco@kernel.org>]

When my em28xx USB device that uses the i2c tvp5150 driver is
disconnected, it crashes.

The cause is that the tvp5150 i2c module uses v4l2_async, but
the em28xx driver does not since it predates v4l2_async.

In that corner case sd->asc_list is empty, so
v4l2_async_unregister_subdev() never calls v4l2_device_unregister_subdev().

Modify the code so that, if sd->asc_list is empty,
v4l2_device_unregister_subdev() is still called.

Fixes: 28a1295795d8 ("media: v4l: async: Allow multiple connections between entities")
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>
---
Changes since v3:
- updated commit message
- added comment to the code

Note: I did not post the other patches in this series, those are unchanged.
---
 drivers/media/v4l2-core/v4l2-async.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-async.c b/drivers/media/v4l2-core/v4l2-async.c
index 888a2e213b08..f36d60e6ff41 100644
--- a/drivers/media/v4l2-core/v4l2-async.c
+++ b/drivers/media/v4l2-core/v4l2-async.c
@@ -898,9 +898,18 @@ void v4l2_async_unregister_subdev(struct v4l2_subdev *sd)
 	sd->subdev_notifier = NULL;

 	if (sd->asc_list.next) {
-		list_for_each_entry_safe(asc, asc_tmp, &sd->asc_list,
-					 asc_subdev_entry) {
-			v4l2_async_unbind_subdev_one(asc->notifier, asc);
+		if (list_empty(&sd->asc_list)) {
+			/*
+			 * If the sub-device was registered through other means
+			 * than v4l2-async, there are no async connections but
+			 * the sub-device may still well be registered.
+			 * Unregister it now.
+			 */
+			v4l2_device_unregister_subdev(sd);
+		} else {
+			list_for_each_entry_safe(asc, asc_tmp, &sd->asc_list,
+						 asc_subdev_entry)
+				v4l2_async_unbind_subdev_one(asc->notifier, asc);
 		}
 	}

-- 
2.53.0