Re: [PATCH RESEND] drm/dp/mst: fix kernel oops when turning off secondary monitor

[Jani Nikula <jani.nikula@intel.com>]

On Tue, 14 Feb 2017, Daniel Vetter <daniel@ffwll.ch> wrote:
> On Tue, Feb 14, 2017 at 02:49:21PM +0200, Jani Nikula wrote:
>> From: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
>> 
>> 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>
>> Cc: <stable@vger.kernel.org> # v3.18+
>> 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>
>
> You haz drm-misc commit rights, pls use them :-)

Sure, I just wanted to have a fresh CI run on this.

> 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.

Will do.

BR,
Jani.

> -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
>> 
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-- 
Jani Nikula, Intel Open Source Technology Center
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