[PATCH v16 05/32] v4l: async: Correctly serialise async sub-device unregistration

[Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>]

The check whether an async sub-device is bound to a notifier was performed
without list_lock held, making it possible for another process to
unbind the async sub-device before the sub-device unregistration function
proceeds to take the lock.

Fix this by first acquiring the lock and then proceeding with the check.

Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
Reviewed-by: Sebastian Reichel <sebastian.reichel@xxxxxxxxxxxxxxx>
Acked-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
---
 drivers/media/v4l2-core/v4l2-async.c | 18 +++++++-----------
 1 file changed, 7 insertions(+), 11 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-async.c b/drivers/media/v4l2-core/v4l2-async.c
index 4924481451ca..cde2cf2ab4b0 100644
--- a/drivers/media/v4l2-core/v4l2-async.c
+++ b/drivers/media/v4l2-core/v4l2-async.c
@@ -298,20 +298,16 @@ EXPORT_SYMBOL(v4l2_async_register_subdev);
 
 void v4l2_async_unregister_subdev(struct v4l2_subdev *sd)
 {
-	struct v4l2_async_notifier *notifier = sd->notifier;
-
-	if (!sd->asd) {
-		if (!list_empty(&sd->async_list))
-			v4l2_async_cleanup(sd);
-		return;
-	}
-
 	mutex_lock(&list_lock);
 
-	list_add(&sd->asd->list, &notifier->waiting);
+	if (sd->asd) {
+		struct v4l2_async_notifier *notifier = sd->notifier;
 
-	if (notifier->unbind)
-		notifier->unbind(notifier, sd, sd->asd);
+		list_add(&sd->asd->list, &notifier->waiting);
+
+		if (notifier->unbind)
+			notifier->unbind(notifier, sd, sd->asd);
+	}
 
 	v4l2_async_cleanup(sd);
 
-- 
2.11.0