linux-kernel - [PATCH 4.9 03/30] media: videobuf2-core: dequeue if start

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Message-Id: <20210813150522.556786043@linuxfoundation.org>
Date:   Fri, 13 Aug 2021 17:06:31 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Hans Verkuil <hverkuil-cisco@...all.nl>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Kieran Bingham <kieran.bingham@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.9 03/30] media: videobuf2-core: dequeue if start_streaming fails

From: Hans Verkuil <hverkuil-cisco@...all.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@...all.nl>
Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Tested-by: Kieran Bingham <kieran.bingham@...asonboard.com>
Fixes: b3379c6201bb ("[media] vb2: only call start_streaming if sufficient buffers are queued")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.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