media: vb2: vb2_core_queue_init(): sanity check lock and wait_prepare/finish

Add two new checks:

1) wait_prepare and wait_finish callbacks are either both present or
   both unset, you can't mix.
2) if lock == NULL, then wait_prepare (and due to check 1 also
   wait_finish) must be present.

These checks should prevent the case where lock == NULL, but there
is no way to release/reacquire whatever lock is used when waiting
for a buffer to arrive in VIDIOC_DQBUF.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Author: Hans Verkuil

drivers/media/common/videobuf2/videobuf2-core.c

@@ -2644,6 +2644,14 @@ int vb2_core_queue_init(struct vb2_queue *q)
 	if (WARN_ON(q->min_reqbufs_allocation > q->max_num_buffers))
 		return -EINVAL;
 
+	/* Either both or none are set */
+	if (WARN_ON(!q->ops->wait_prepare ^ !q->ops->wait_finish))
+		return -EINVAL;
+
+	/* Warn if q->lock is NULL and no custom wait_prepare is provided */
+	if (WARN_ON(!q->lock && !q->ops->wait_prepare))
+		return -EINVAL;
+
 	INIT_LIST_HEAD(&q->queued_list);
 	INIT_LIST_HEAD(&q->done_list);
 	spin_lock_init(&q->done_lock);