Unfortunately drm_dp_get_mst_branch_device which is called from both drm_dp_mst_handle_down_rep and drm_dp_mst_handle_up_rep seem to rely on that mgr->mst_primary is not NULL, which seem to be wrong as it can be cleared with simultaneous mode set, if probing fails or in other case. mgr->lock mutex doesn't protect against that as it might just get assigned to NULL right before, not simultaneously. There are currently bugs 107738, 108816 bugs which crash in drm_dp_get_mst_branch_device, caused by this issue. Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@xxxxxxxxx> --- drivers/gpu/drm/drm_dp_mst_topology.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c index 5ff1d79b86c4..fb90ed4cdc3a 100644 --- a/drivers/gpu/drm/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/drm_dp_mst_topology.c @@ -1273,6 +1273,12 @@ static struct drm_dp_mst_branch *drm_dp_get_mst_branch_device(struct drm_dp_mst_ /* find the port by iterating down */ mutex_lock(&mgr->lock); + + if (!mgr->mst_primary) { + mstb = NULL; + goto out; + } + mstb = mgr->mst_primary; for (i = 0; i < lct - 1; i++) { -- 2.17.1 _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel