[PATCH v7 07/19] media: meson: vdec: Refactor esparser work queue and fix teardown race

[Anand Moon <linux.amoon@gmail.com>]

Rework the esparser work queue logic to prevent concurrent queue mutations
and fix a race condition during streaming teardown.

The previous implementation relied on v4l2_m2m_for_each_src_buf_safe(),
which held the session mutex across the entire queue traversal. This
blocked concurrent operations, caused inaccurate buffer mapping, and
triggered 100+ second watchdog freezes due to an unyielding polling loop.
Additionally, the low-level parser handled buffer ownership adjustments
and completion callbacks directly, leading to inconsistent error paths and
races between streamon and streamoff.

Fix this by utilizing the modern scoped_guard(mutex) mechanism inside the
main worker loop. This allows the session lock to be automatically
dropped on any conditional breakout path, preventing voluntary scheduling
bugs while invoking cond_resched(). De-couple buffer lifecycles from the
hardware parser routine by leveraging safe, linear fetches via
v4l2_m2m_next_src_buf() and v4l2_m2m_src_buf_remove(), ensuring orderly
frame transactions. Refactor esparser_queue() to return explicit error
codes (such as -EBADMSG, -EIO, and -EAGAIN) to safely handle buffer states.

Clean up teardown paths: Execute cancel_work_sync() inside
vdec_stop_streaming() and vdec_close() immediately after
synchronize_irq(). This ensures any pending scheduled queue work is fully
flushed and canceled before the driver destroys hardware instances.

Cc: Nicolas Dufresne <nicolas@ndufresne.ca>
Signed-off-by: Anand Moon <linux.amoon@gmail.com>
---
 drivers/staging/media/meson/vdec/esparser.c | 69 +++++++++++++++------
 1 file changed, 49 insertions(+), 20 deletions(-)

diff --git a/drivers/staging/media/meson/vdec/esparser.c b/drivers/staging/media/meson/vdec/esparser.c
index 37749ede308c6..e5d3d817b9b2b 100644
--- a/drivers/staging/media/meson/vdec/esparser.c
+++ b/drivers/staging/media/meson/vdec/esparser.c
@@ -328,15 +328,11 @@ esparser_queue(struct amvdec_session *sess, struct vb2_v4l2_buffer *vbuf)
 		return -EAGAIN;
 	}
 
-	v4l2_m2m_src_buf_remove_by_buf(sess->m2m_ctx, vbuf);
-
 	offset = esparser_get_offset(sess);
 
 	ret = amvdec_add_ts(sess, vb->timestamp, vbuf->timecode, offset, vbuf->flags);
-	if (ret) {
-		v4l2_m2m_buf_done(vbuf, VB2_BUF_STATE_ERROR);
+	if (ret)
 		return ret;
-	}
 
 	dev_dbg(core->dev, "esparser: ts = %llu pld_size = %u offset = %08X flags = %08X\n",
 		vb->timestamp, payload_size, offset, vbuf->flags);
@@ -348,12 +344,10 @@ esparser_queue(struct amvdec_session *sess, struct vb2_v4l2_buffer *vbuf)
 	if (sess->fmt_out->pixfmt == V4L2_PIX_FMT_VP9) {
 		payload_size = vp9_update_header(core, vb);
 
-		/* If unable to alter buffer to add headers */
 		if (payload_size == 0) {
+			dev_err(core->dev, "esparser: VP9 header update failed\n");
 			amvdec_remove_ts(sess, vb->timestamp);
-			v4l2_m2m_buf_done(vbuf, VB2_BUF_STATE_ERROR);
-
-			return 0;
+			return -EBADMSG;
 		}
 	}
 
@@ -363,33 +357,68 @@ esparser_queue(struct amvdec_session *sess, struct vb2_v4l2_buffer *vbuf)
 	if (ret <= 0) {
 		dev_warn(core->dev, "esparser: input parsing error\n");
 		amvdec_remove_ts(sess, vb->timestamp);
-		v4l2_m2m_buf_done(vbuf, VB2_BUF_STATE_ERROR);
 		amvdec_write_parser(core, PARSER_FETCH_CMD, 0);
-
-		return 0;
+		return -EIO;
 	}
 
 	atomic_inc(&sess->esparser_queued_bufs);
-	v4l2_m2m_buf_done(vbuf, VB2_BUF_STATE_DONE);
 
 	return 0;
 }
 
 void esparser_queue_all_src(struct work_struct *work)
 {
-	struct v4l2_m2m_buffer *buf, *n;
 	struct amvdec_session *sess =
 		container_of(work, struct amvdec_session, esparser_queue_work);
+	struct device *dev = sess->core->dev_dec;
+	int ret;
 
-	mutex_lock(&sess->lock);
-	v4l2_m2m_for_each_src_buf_safe(sess->m2m_ctx, buf, n) {
-		if (sess->should_stop)
-			break;
+	while (1) {
+		struct vb2_v4l2_buffer *vbuf = NULL;
+		bool processed_frame = false;
+
+		scoped_guard(mutex, &sess->lock) {
+			/* Safe atomic tracking check: exit loop if session is shutting down */
+			if (sess->should_stop)
+				return;
+
+			/* Queue completely empty: exit work loop cleanly */
+			vbuf = v4l2_m2m_next_src_buf(sess->m2m_ctx);
+			if (!vbuf)
+				break;
+
+			/* Stop processing if we hit the end-of-stream drain buffer */
+			if (vbuf->flags & V4L2_BUF_FLAG_LAST)
+				break;
+
+			/* Check hardware FIFO limits safely inside the locks */
+			ret = esparser_queue(sess, vbuf);
+			if (ret == -EAGAIN)
+				break;
+
+			/* Pop the buffer from the source queue since it is now processed */
+			vbuf = v4l2_m2m_src_buf_remove(sess->m2m_ctx);
+			if (!vbuf) {
+				dev_dbg(dev, "Buffer missing during queue removal\n");
+				break;
+			}
+
+			/* Complete the buffer transaction based on parser results */
+			if (ret < 0)
+				v4l2_m2m_buf_done(vbuf, VB2_BUF_STATE_ERROR);
+			else
+				v4l2_m2m_buf_done(vbuf, VB2_BUF_STATE_DONE);
 
-		if (esparser_queue(sess, &buf->vb) < 0)
+			/* Set tracking flag indicating transaction completion */
+			processed_frame = true;
+		}
+
+		if (processed_frame)
 			break;
+
+		/* Give other threads and IRQ routines a window to execute while unlocked */
+		cond_resched();
 	}
-	mutex_unlock(&sess->lock);
 }
 
 int esparser_power_up(struct amvdec_session *sess)
-- 
2.50.1