[PATCH] drm/amd/display: Fix deadlock with display during hanged ring recovery.

[Grodzovsky, Andrey]

On 2/14/19 11:07 AM, Michel Dänzer wrote:
> On 2019-02-14 4:54 p.m., Kazlauskas, Nicholas wrote:
>> On 2/14/19 10:42 AM, Grodzovsky, Andrey wrote:
>>> On 2/14/19 4:05 AM, Christian König wrote:
>>>> Am 13.02.19 um 19:58 schrieb Andrey Grodzovsky:
>>>>> When ring hang happens amdgpu_dm_commit_planes during flip is holding
>>>>> the BO reserved and then stack waiting for fences to signal in
>>>>> reservation_object_wait_timeout_rcu (which won't signal because there
>>>>> was a hnag). Then when we try to shutdown display block during reset
>>>>> recovery from drm_atomic_helper_suspend we also try to reserve the BO
>>>>> from dm_plane_helper_cleanup_fb ending in deadlock.
>>>>> Also remove useless WARN_ON
>>>> Well it is good that you pointed this out, but there are more problems
>>>> than just waiting wile the BO is reserved here.
>>>>
>>>>> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky at amd.com>
>>>>> ---
>>>>>     drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 19
>>>>> +++++++++++++------
>>>>>     1 file changed, 13 insertions(+), 6 deletions(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>>>>> b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>>>>> index acc4ff8..f8dec36 100644
>>>>> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>>>>> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>>>>> @@ -4802,14 +4802,21 @@ static void amdgpu_dm_commit_planes(struct
>>>>> drm_atomic_state *state,
>>>>>                  */
>>>>>                 abo = gem_to_amdgpu_bo(fb->obj[0]);
>>>>>                 r = amdgpu_bo_reserve(abo, true);
>>>> Well why do we reserve the BO in the first place? As the name
>>>> indicates reservation_object_wait_timeout_rcu() just uses rcu to wait
>>>> for the BO to be idle, no need to actually reserve it at all.
>>> That a good point, I honestly can't remember any more why it's here...
>>> It does look unnecessary given that we are not validating the BO here.
>> I think we reserve it to grab the tiling flags to update the plane
>> address (and some other bits of the plane state with a patch I'm
>> currently working on). I'm guessing that we still need the reservation
>> so nothing else tries to grab it after it becomes idle, but I'm not
>> overly familiar with that bit.
> The BO is already pinned at this point, isn't it? That's enough to
> prevent it from moving, no reservation needed.


Yes, agree.

Andrey


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