diff --git a/kernel/daedalus_v4l2_main.c b/kernel/daedalus_v4l2_main.c
index b493a4b..6eb021a 100644
--- a/kernel/daedalus_v4l2_main.c
+++ b/kernel/daedalus_v4l2_main.c
@@ -149,6 +149,17 @@ struct daedalus_ctx {
 	struct v4l2_m2m_ctx		*m2m_ctx;
 	struct v4l2_ctrl_handler	hdl;
 
+	/*
+	 * Per-context vb2 queue lock.  Was originally pointed at the
+	 * device-wide dev->m2m_lock, which serialised vb2 ioctls across
+	 * every concurrent client — Firefox spawns multiple content/RDD
+	 * processes that each open /dev/video0, and a device-wide lock
+	 * made S_FMT / REQBUFS / QBUF on one client block (and sometimes
+	 * EBUSY-fail) against another client mid-stream.  cedrus / rkvdec
+	 * / hantro all use per-ctx vb mutexes for exactly this reason.
+	 */
+	struct mutex			vb_mutex;
+
 	struct v4l2_pix_format_mplane	src_fmt;
 	struct v4l2_pix_format_mplane	dst_fmt;
 };
@@ -523,7 +534,9 @@ static int daedalus_queue_init(void *priv, struct vb2_queue *src_vq,
 	 */
 	src_vq->mem_ops		 = &vb2_dma_contig_memops;
 	src_vq->timestamp_flags	 = V4L2_BUF_FLAG_TIMESTAMP_COPY;
-	src_vq->lock		 = &ctx->dev->m2m_lock;
+	/* Per-ctx lock so concurrent clients don't serialise on a
+	 * device-wide mutex.  See struct daedalus_ctx.vb_mutex comment. */
+	src_vq->lock		 = &ctx->vb_mutex;
 	src_vq->dev		 = &ctx->dev->pdev->dev;
 	src_vq->allow_cache_hints = 1;
 
@@ -538,7 +551,7 @@ static int daedalus_queue_init(void *priv, struct vb2_queue *src_vq,
 	dst_vq->ops		 = &daedalus_qops;
 	dst_vq->mem_ops		 = &vb2_dma_contig_memops;
 	dst_vq->timestamp_flags	 = V4L2_BUF_FLAG_TIMESTAMP_COPY;
-	dst_vq->lock		 = &ctx->dev->m2m_lock;
+	dst_vq->lock		 = &ctx->vb_mutex;
 	dst_vq->dev		 = &ctx->dev->pdev->dev;
 	dst_vq->allow_cache_hints = 1;
 
@@ -1112,6 +1125,7 @@ static int daedalus_open(struct file *file)
 	if (!ctx)
 		return -ENOMEM;
 	ctx->dev = dev;
+	mutex_init(&ctx->vb_mutex);
 
 	v4l2_fh_init(&ctx->fh, &dev->vdev);
 	file->private_data = &ctx->fh;
@@ -1159,6 +1173,7 @@ static int daedalus_open(struct file *file)
 err_ctrl:
 	v4l2_ctrl_handler_free(&ctx->hdl);
 	v4l2_fh_exit(&ctx->fh);
+	mutex_destroy(&ctx->vb_mutex);
 	kfree(ctx);
 	return ret;
 }
@@ -1175,6 +1190,7 @@ static int daedalus_release(struct file *file)
 	v4l2_m2m_ctx_release(ctx->m2m_ctx);
 	v4l2_ctrl_handler_free(&ctx->hdl);
 	v4l2_fh_exit(&ctx->fh);
+	mutex_destroy(&ctx->vb_mutex);
 	kfree(ctx);
 	return 0;
 }