[PATCH] drm/msm: move submit fence wait out of struct_mutex

[Rob Clark]

On Sat, Feb 25, 2017 at 12:36 PM, Daniel Vetter <daniel at ffwll.ch> wrote:
> On Sat, Feb 25, 2017 at 4:43 PM, Rob Clark <robdclark at gmail.com> wrote:
>> Probably a symptom of needing finer grained locking, but if we wait on
>> the incoming fence-fd (which could come from a different context) while
>> holding struct_mutex, that blocks retire_worker so gpu fences cannot get
>> scheduled.
>>
>> This causes a problem if userspace manages to get more than a frame
>> ahead, leaving the atomic-commit worker blocked waiting on fences that
>> cannot be signaled because submit is blocked waiting for a fence
>> signalled from vblank (after the atomic commit which is blocked).
>>
>> If we start having multiple fence ctxs for the gpu, submit_fence_sync()
>> would probably need to move outside of struct_mutex as well.
>>
>> Signed-off-by: Rob Clark <robdclark at gmail.com>
>
> It's unfortunately not yet landed, but as soon as it's there I think
> we should annotate fences using the cross-release stuff that's
> cooking:
>
> https://lwn.net/Articles/708628/
>
> That should be able to catch deps between waiter/signaller vs. locking.

ohh, that would be spiffy

BR,
-R