On Tue, Feb 14, 2017 at 02:49:21PM +0200, Jani Nikula wrote:
> From: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>
>
> 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>
> Cc: <stable@xxxxxxxxxxxxxxx> # v3.18+
> 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>
You haz drm-misc commit rights, pls use them :-)
Since it doesn't have deps, probably simplest to smash into drm-misc-fixes
and then send a pull req to Dave right away. If you want, you can roll
-fixes forward to -rc8 while at it.
-Daniel
> ---
> 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 122a1b04bebc..f2cc375907d0 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;
> }
> --
> 2.1.4
>
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch