[PATCH 2/2] drm: Revert syncobj timeline changes.

[Christian König]

Am 09.11.18 um 23:26 schrieb Eric Anholt:
> Eric Anholt <eric at anholt.net> writes:
>
>> [ Unknown signature status ]
>> zhoucm1 <zhoucm1 at amd.com> writes:
>>
>>> On 2018年11月09日 00:52, Christian König wrote:
>>>> Am 08.11.18 um 17:07 schrieb Koenig, Christian:
>>>>> Am 08.11.18 um 17:04 schrieb Eric Anholt:
>>>>>> Daniel suggested I submit this, since we're still seeing regressions
>>>>>> from it.  This is a revert to before 48197bc564c7 ("drm: add syncobj
>>>>>> timeline support v9") and its followon fixes.
>>>>> This is a harmless false positive from lockdep, Chouming and I are
>>>>> already working on a fix.
>>>> On the other hand we had enough trouble with that patch, so if it
>>>> really bothers you feel free to add my Acked-by: Christian König
>>>> <christian.koenig at amd.com> and push it.
>>> NAK, please no, I don't think this needed, the Warning totally isn't
>>> related to syncobj timeline, but fence-array implementation flaw, just
>>> exposed by syncobj.
>>> In addition, Christian already has a fix for this Warning, I've tested.
>>> Please Christian send to public review.
>> I backed out my revert of #2 (#1 still necessary) after adding the
>> lockdep regression fix, and now my CTS run got oomkilled after just a
>> few hours, with these notable lines in the unreclaimable slab info list:
>>
>> [ 6314.373099] drm_sched_fence        69095KB      69095KB
>> [ 6314.373653] kmemleak_object       428249KB     428384KB
>> [ 6314.373736] kmalloc-262144           256KB        256KB
>> [ 6314.373743] kmalloc-131072           128KB        128KB
>> [ 6314.373750] kmalloc-65536             64KB         64KB
>> [ 6314.373756] kmalloc-32768           1472KB       1728KB
>> [ 6314.373763] kmalloc-16384             64KB         64KB
>> [ 6314.373770] kmalloc-8192             208KB        208KB
>> [ 6314.373778] kmalloc-4096            2408KB       2408KB
>> [ 6314.373784] kmalloc-2048             288KB        336KB
>> [ 6314.373792] kmalloc-1024            1457KB       1512KB
>> [ 6314.373800] kmalloc-512              854KB       1048KB
>> [ 6314.373808] kmalloc-256              188KB        268KB
>> [ 6314.373817] kmalloc-192            69141KB      69142KB
>> [ 6314.373824] kmalloc-64             47703KB      47704KB
>> [ 6314.373886] kmalloc-128            46396KB      46396KB
>> [ 6314.373894] kmem_cache                31KB         35KB
>>
>> No results from kmemleak, though.
> OK, it looks like the #2 revert probably isn't related to the OOM issue.
> Running a single job on otherwise unused DRM, watching /proc/slabinfo
> every second for drm_sched_fence, I get:
>
> drm_sched_fence        0      0    192   21    1 : tunables   32   16    8 : slabdata      0      0      0 : globalstat       0      0     0    0    0    0    0    0    0 : cpustat      0      0      0      0
> drm_sched_fence       16     21    192   21    1 : tunables   32   16    8 : slabdata      1      1      0 : globalstat      16     16     1    0    0    0    0    0    0 : cpustat      5      1      6      0
> drm_sched_fence       13     21    192   21    1 : tunables   32   16    8 : slabdata      1      1      0 : globalstat      16     16     1    0    0    0    0    0    0 : cpustat      5      1      6      0
> drm_sched_fence        6     21    192   21    1 : tunables   32   16    8 : slabdata      1      1      0 : globalstat      16     16     1    0    0    0    0    0    0 : cpustat      5      1      6      0
> drm_sched_fence        4     21    192   21    1 : tunables   32   16    8 : slabdata      1      1      0 : globalstat      16     16     1    0    0    0    0    0    0 : cpustat      5      1      6      0
> drm_sched_fence        2     21    192   21    1 : tunables   32   16    8 : slabdata      1      1      0 : globalstat      16     16     1    0    0    0    0    0    0 : cpustat      5      1      6      0
> drm_sched_fence        0     21    192   21    1 : tunables   32   16    8 : slabdata      0      1      0 : globalstat      16     16     1    0    0    0    0    0    0 : cpustat      5      1      6      0
>
> So we generate a ton of fences, and I guess free them slowly because of
> RCU?  And presumably kmemleak was sucking up lots of memory because of
> how many of these objects were laying around.

That is certainly possible. Another possibility is that we don't drop 
the reference in dma-fence-array early enough.

E.g. the dma-fence-array will keep the reference to its fences until it 
is destroyed, which is a bit late when you chain multiple 
dma-fence-array objects together.

David can you take a look at this and propose a fix? That would probably 
be good to have fixed in dma-fence-array separately to the timeline work.

Thanks,
Christian.

>
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