Op 29-06-17 om 11:44 schreef Daniel Vetter:
> On Thu, Jun 29, 2017 at 11:33 AM, Maarten Lankhorst
> <maarten.lankho...@linux.intel.com> wrote:
>> Op 29-06-17 om 11:23 schreef Daniel Vetter:
>>> On Thu, Jun 29, 2017 at 11:10 AM, Maarten Lankhorst
>>> <maarten.lankho...@linux.intel.com> wrote:
>>>> Op 27-06-17 om 16:59 schreef Daniel Vetter:
>>>>> From: Thierry Reding <tred...@nvidia.com>
>>>>>
>>>>> Move the modeset locking from drivers into FB helpers.
>>>>>
>>>>> v2: Also handle intel_connector_add_to_fbdev.
>>>>>
>>>>> Tested-by: John Stultz <john.stu...@linaro.org>
>>>>> Signed-off-by: Thierry Reding <tred...@nvidia.com> (v1)
>>>>> Signed-off-by: Daniel Vetter <daniel.vet...@ffwll.ch>
>>>>> ---
>>>>> drivers/gpu/drm/drm_fb_helper.c | 40
>>>>> +++++++++++++++++++++++++++++-----
>>>>> drivers/gpu/drm/i915/intel_dp_mst.c | 6 -----
>>>>> drivers/gpu/drm/radeon/radeon_dp_mst.c | 7 ------
>>>>> 3 files changed, 34 insertions(+), 19 deletions(-)
>>>> I know we suck at DP-MST. But I fear the unregister leaves open a race
>>>> with mst_port being unset without connection_mutex..
>>>>
>>>> best_encoder() and mode_valid() appear to use it. It's probably harmless
>>>> and I have no good solution, so maybe just annotate it in the patch? Might
>>>> also affect i915_hpd_poll_init_work, though I think the race in itself is
>>>> harmless.
>>> Hm, but this did race even before that already ... Should I just wrap
>>> the mst_port = NULL in the connection_mutex? With a big warning that
>>> we should have proper refcounting for this instead (both connectors
>>> and all the mst things are refcounted already).
>>> -Daniel
>> I think leave open the race, the DP-MST modeset code itself doesn't use the
>> connector->mst_port, just the detect callbacks do. In case of nonblocking
>> modeset mst_port might already fall away so it's not like the race is any
>> worse now.
>>
>> I don't even know how to solve it, except by not unplugging. :)
> Why does grabbing the lock not fix the race? ->detect eventually calls
> drm_dp_get_validated_port_ref, which will bail on a zombie mst port..
Oh ok. But there will always be a race. If DP-MST fails immediately after
drm_dp_get_validated_port_ref,
you'd still not be able to do anything about it. :)
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