From 00fb1727c108c9dc8e6abf7096bcbc527905e5b0 Mon Sep 17 00:00:00 2001 From: Pierre-Louis Bossart Date: Sun, 4 Dec 2016 19:01:36 -0600 Subject: [PATCH v2] drm/dp/mst: fix kernel oops when turning off secondary monitor 100% reproducible issue found on SKL SkullCanyon NUC with two external DP daisy-chained monitors in DP/MST mode. When turning off or changing the input of the second monitor the machine stops with a kernel oops. This issue happened with 4.8.8 as well as drm/drm-intel-nightly. This issue is traced to an inconsistent control flow in drm_dp_update_payload_part1(): the 'port' pointer is set to NULL at the same time as 'req_payload.num_slots' is set to zero, but the pointer is dereferenced even when req_payload.num_slot is zero. The problematic dereference was introduced in commit dfda0df34 ("drm/mst: rework payload table allocation to conform better") and may impact all versions since v3.18 The fix suggested by Chris Wilson removes the kernel oops and was found to work well after 10mn of monkey-testing with the second monitor power and input buttons Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=98990 Cc: Dave Airlie Signed-off-by: Pierre-Louis Bossart --- drivers/gpu/drm/drm_dp_mst_topology.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c index aa64448..f59771d 100644 --- a/drivers/gpu/drm/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/drm_dp_mst_topology.c @@ -1817,7 +1817,7 @@ int drm_dp_update_payload_part1(struct drm_dp_mst_topology_mgr *mgr) mgr->payloads[i].vcpi = req_payload.vcpi; } else if (mgr->payloads[i].num_slots) { mgr->payloads[i].num_slots = 0; - drm_dp_destroy_payload_step1(mgr, port, port->vcpi.vcpi, &mgr->payloads[i]); + drm_dp_destroy_payload_step1(mgr, port, mgr->payloads[i].vcpi, &mgr->payloads[i]); req_payload.payload_state = mgr->payloads[i].payload_state; mgr->payloads[i].start_slot = 0; } -- 2.7.4