This is a note to let you know that I've just added the patch titled drm/dp/mst: fix kernel oops when turning off secondary monitor to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: drm-dp-mst-fix-kernel-oops-when-turning-off-secondary-monitor.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From bb08c04dc867b5f392caec635c097d5d5fcd8c9f Mon Sep 17 00:00:00 2001 From: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx> Date: Tue, 14 Feb 2017 14:49:21 +0200 Subject: drm/dp/mst: fix kernel oops when turning off secondary monitor From: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx> commit bb08c04dc867b5f392caec635c097d5d5fcd8c9f upstream. 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 Fixes: dfda0df34264 ("drm/mst: rework payload table allocation to conform better.") Cc: Dave Airlie <airlied@xxxxxxxxxx> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> Cc: Nathan D Ciobanu <nathan.d.ciobanu@xxxxxxxxxxxxxxx> Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@xxxxxxxxx> Cc: Sean Paul <seanpaul@xxxxxxxxxxxx> Tested-by: Nathan D Ciobanu <nathan.d.ciobanu@xxxxxxxxxxxxxxx> Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@xxxxxxxxx> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx> Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx> Link: http://patchwork.freedesktop.org/patch/msgid/1487076561-2169-1-git-send-email-jani.nikula@xxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/gpu/drm/drm_dp_mst_topology.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- 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 d 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; } Patches currently in stable-queue which might be from pierre-louis.bossart@xxxxxxxxxxxxxxx are queue-4.9/drm-dp-mst-fix-kernel-oops-when-turning-off-secondary-monitor.patch