[PATCH] staging: most: video: replace BUG_ON with WARN_ON_ONCE and add recovery

[Matan Cohen <matan@matanco.space>]

BUG_ON() halts the kernel unconditionally. The check after
most_deregister_component() guards against a bug in mostcore: it
currently does not call disconnect_channel() for linked channels on
deregistration, so if that ever changes unexpectedly, video_devices
could be non-empty.

Replace BUG_ON with WARN_ON_ONCE so the kernel stays up, and add a
recovery path that drains and frees any remaining devices to avoid
memory leaks in that error case.

Also document what the spinlock and mutex in struct most_video_dev
each protect.
---
 drivers/staging/most/video/video.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/most/video/video.c b/drivers/staging/most/video/video.c
index 04351f8ccccf1..4ade49569bd63 100644
--- a/drivers/staging/most/video/video.c
+++ b/drivers/staging/most/video/video.c
@@ -33,14 +33,14 @@ struct most_video_dev {
 	bool mute;
 
 	struct list_head pending_mbos;
-	spinlock_t list_lock;
+	spinlock_t list_lock; /* protects pending_mbos and mute */
 
 	struct v4l2_device v4l2_dev;
 	atomic_t access_ref;
 	struct video_device *vdev;
 	unsigned int ctrl_input;
 
-	struct mutex lock;
+	struct mutex lock; /* v4l2 device lock */
 
 	wait_queue_head_t wait_data;
 };
@@ -577,7 +577,20 @@ static void __exit comp_exit(void)
 
 	most_deregister_configfs_subsys(&comp);
 	most_deregister_component(&comp);
-	BUG_ON(!list_empty(&video_devices));
+
+	if (WARN_ON_ONCE(!list_empty(&video_devices))) {
+		/* clean up any devices unexpectedly added during deregister phase */
+		spin_lock_irq(&list_lock);
+		list_replace_init(&video_devices, &free_list);
+		spin_unlock_irq(&list_lock);
+
+		list_for_each_entry_safe(mdev, tmp, &free_list, list) {
+			list_del_init(&mdev->list);
+			comp_unregister_videodev(mdev);
+			v4l2_device_disconnect(&mdev->v4l2_dev);
+			v4l2_device_put(&mdev->v4l2_dev);
+		}
+	}
 }
 
 module_init(comp_init);
-- 
2.43.0