[PATCH 4.9 03/30] media: videobuf2-core: dequeue if start_streaming fails

Greg Kroah-Hartman
2021-08-13T15:10:20Z

From: Hans Verkuil <hverkuil-cisco@xs4all.nl>

[ Upstream commit c592b46907adbeb81243f7eb7a468c36692658b8 ]

If a vb2_queue sets q->min_buffers_needed then when the number of
queued buffers reaches q->min_buffers_needed, vb2_core_qbuf() will call
the start_streaming() callback. If start_streaming() returns an error,
then that error was just returned by vb2_core_qbuf(), but the buffer
was still queued. However, userspace expects that if VIDIOC_QBUF fails,
the buffer is returned dequeued.

So if start_streaming() fails, then remove the buffer from the queue,
thus avoiding this unwanted side-effect.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Fixes: b3379c6201bb ("[media] vb2: only call start_streaming if sufficient buffers are queued")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/media/v4l2-core/videobuf2-core.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
index b1a4d4e2341b..3ac9f7260e72 100644
--- a/drivers/media/v4l2-core/videobuf2-core.c
+++ b/drivers/media/v4l2-core/videobuf2-core.c
@@ -1370,6 +1370,7 @@ static int vb2_start_streaming(struct vb2_queue *q)
int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb)
{
struct vb2_buffer *vb;
+ enum vb2_buffer_state orig_state;
int ret;

if (q->error) {
@@ -1399,6 +1400,7 @@ int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb)
* Add to the queued buffers list, a buffer will stay on it until
* dequeued in dqbuf.
*/
+ orig_state = vb->state;
list_add_tail(&vb->queued_entry, &q->queued_list);
q->queued_count++;
q->waiting_for_buffers = false;
@@ -1429,8 +1431,17 @@ int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb)
if (q->streaming && !q->start_streaming_called &&
q->queued_count >= q->min_buffers_needed) {
ret = vb2_start_streaming(q);
- if (ret)
+ if (ret) {
+ /*
+ * Since vb2_core_qbuf will return with an error,
+ * we should return it to state DEQUEUED since
+ * the error indicates that the buffer wasn't queued.
+ */
+ list_del(&vb->queued_entry);
+ q->queued_count--;
+ vb->state = orig_state;
return ret;
+ }
}

dprintk(1, "qbuf of buffer %d succeeded\n", vb->index);
--
2.30.2