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

[Lyude Paul]

Reviewed-by: Lyude Paul <lyude at redhat.com>

Guessing it's fine if I push this with your sob and review added?

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]);

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat