[PATCH] drm/ttm: Remove pinned bos from LRU in ttm_bo_move_to_lru_tail() v2

[Christian König]

Am 05.01.21 um 19:12 schrieb Lyude Paul:
> Reviewed-by: Lyude Paul <lyude at redhat.com>
>
> Guessing it's fine if I push this with your sob and review added?

Works for me, just take care that you pick the right branch.

I always seem to push my stuff into the wrong one.

Christian.

>
> On Tue, 2021-01-05 at 12:45 +0100, Christian König wrote:
>> From: Lyude Paul <lyude at redhat.com>
>>
>> Recently a regression was introduced which caused TTM's buffer eviction to
>> attempt to evict already-pinned BOs, causing issues with buffer eviction
>> under memory pressure along with suspend/resume:
>>
>>    nouveau 0000:1f:00.0: DRM: evicting buffers...
>>    nouveau 0000:1f:00.0: DRM: Moving pinned object 00000000c428c3ff!
>>    nouveau 0000:1f:00.0: fifo: fault 00 [READ] at 0000000000200000 engine 04
>>    [BAR1] client 07 [HUB/HOST_CPU] reason 02 [PTE] on channel -1 [00ffeaa000
>>    unknown]
>>    nouveau 0000:1f:00.0: fifo: DROPPED_MMU_FAULT 00001000
>>    nouveau 0000:1f:00.0: fifo: fault 01 [WRITE] at 0000000000020000 engine
>>    0c [HOST6] client 07 [HUB/HOST_CPU] reason 02 [PTE] on channel 1
>>    [00ffb28000 DRM]
>>    nouveau 0000:1f:00.0: fifo: channel 1: killed
>>    nouveau 0000:1f:00.0: fifo: runlist 0: scheduled for recovery
>>    [TTM] Buffer eviction failed
>>    nouveau 0000:1f:00.0: DRM: waiting for kernel channels to go idle...
>>    nouveau 0000:1f:00.0: DRM: failed to idle channel 1 [DRM]
>>    nouveau 0000:1f:00.0: DRM: resuming display...
>>
>> After some bisection and investigation, it appears this resulted from the
>> recent changes to ttm_bo_move_to_lru_tail(). Previously when a buffer was
>> pinned, the buffer would be removed from the LRU once ttm_bo_unreserve
>> to maintain the LRU list when pinning or unpinning BOs. However, since:
>>
>> commit 3d1a88e1051f ("drm/ttm: cleanup LRU handling further")
>>
>> We've been exiting from ttm_bo_move_to_lru_tail() at the very beginning of
>> the function if the bo we're looking at is pinned, resulting in the pinned
>> BO never getting removed from the lru and as a result - causing issues when
>> it eventually becomes time for eviction.
>>
>> So, let's fix this by calling ttm_bo_del_from_lru() from
>> ttm_bo_move_to_lru_tail() in the event that we're dealing with a pinned
>> buffer.
>>
>> v2 (chk): reduce to only the fixing one liner since we always want to
>> call the callback whenever we would move on the LRU.
>>
>> Signed-off-by: Lyude Paul <lyude at redhat.com>
>> Fixes: 3d1a88e1051f ("drm/ttm: cleanup LRU handling further")
>> Cc: Christian König <christian.koenig at amd.com>
>> Cc: Dave Airlie <airlied at redhat.com>
>> ---
>>   drivers/gpu/drm/ttm/ttm_bo.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
>> index 31e8b3da5563..b65f4b12f986 100644
>> --- a/drivers/gpu/drm/ttm/ttm_bo.c
>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
>> @@ -138,8 +138,10 @@ void ttm_bo_move_to_lru_tail(struct ttm_buffer_object
>> *bo,
>>   
>>          dma_resv_assert_held(bo->base.resv);
>>   
>> -       if (bo->pin_count)
>> +       if (bo->pin_count) {
>> +               ttm_bo_del_from_lru(bo);
>>                  return;
>> +       }
>>   
>>          man = ttm_manager_type(bdev, mem->mem_type);
>>          list_move_tail(&bo->lru, &man->lru[bo->priority]);