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

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

On Wed, 15 Feb 2017, Jani Nikula <jani.nikula@intel.com> wrote:
> 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.

And pushed to drm-misc-fixes, thanks for the patch, review and testing.

BR,
Jani.



-- 
Jani Nikula, Intel Open Source Technology Center
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