Re: [PATCH] fix: drm/display: drm_dp_mst_topology_mgr_set_mst: error path after DPCD write failure leaks MST branch device reference

[WenTao Liang]

> 2026年6月26日 20:51，WenTao Liang <vulab@xxxxxxxxxxx> 写道：
> 
> drm_dp_add_mst_branch_device initializes mstb with refcount 1, and
>  drm_dp_mst_topology_get_mstb increments it to 2. When
>  drm_dp_dpcd_write_byte fails, out_unlock performs only one
>  drm_dp_mst_topology_put_mstb, leaving the other reference stored in
>  mgr->mst_primary. Since MST was not successfully enabled, no disable path
>  will clean it up.
> 
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 7a3cbf590e63 ("drm/mst: Some style improvements in drm_dp_mst_topology_mgr_set_mst()")
> Signed-off-by: WenTao Liang <vulab@xxxxxxxxxxx>
> ---
> drivers/gpu/drm/display/drm_dp_mst_topology.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c
> index 8757972e8e24..db9441c80cd5 100644
> --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
> @@ -3679,8 +3679,10 @@ int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr, bool ms
> 					     DP_MST_EN |
> 					     DP_UP_REQ_EN |
> 					     DP_UPSTREAM_IS_SRC);
> -		if (ret < 0)
> +		if (ret < 0) {
> +			mgr->mst_primary = NULL;
> 			goto out_unlock;
> +		}
> 
> 		/* Write reset payload */
> 		drm_dp_dpcd_clear_payload(mgr->aux);
> -- 
> 2.39.5 (Apple Git-154)

Please ignore this patch. I will resend a proper version after
learning the kernel submission process.

Apologies for the noise.

Best regards,
WenTao Liang