Patch "drm/dp/mst: fix kernel oops when turning off secondary monitor" has been added to the 4.4-stable tree

Patch "drm/dp/mst: fix kernel oops when turning off secondary monitor" has been added to the 4.4-stable tree

[gregkh]

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 4.4-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-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From bb08c04dc867b5f392caec635c097d5d5fcd8c9f Mon Sep 17 00:00:00 2001
From: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
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@linux.intel.com>

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@redhat.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Nathan D Ciobanu <nathan.d.ciobanu@linux.intel.com>
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Cc: Sean Paul <seanpaul@chromium.org>
Tested-by: Nathan D Ciobanu <nathan.d.ciobanu@linux.intel.com>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1487076561-2169-1-git-send-email-jani.nikula@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 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
@@ -1812,7 +1812,7 @@ int drm_dp_update_payload_part1(struct d
 				mgr->payloads[i].num_slots = req_payload.num_slots;
 			} 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@linux.intel.com are

queue-4.4/drm-dp-mst-fix-kernel-oops-when-turning-off-secondary-monitor.patch