[PATCH 1/2] drm/ttm: fix locking in vmap/vunmap TTM GEM helpers

[Thomas Zimmermann]

Hi

Am 15.07.22 um 13:15 schrieb Christian König:
> I've stumbled over this while reviewing patches for DMA-buf and it looks
> like we completely messed the locking up here.
> 
> In general most TTM function should only be called while holding the
> appropriate BO resv lock. Without this we could break the internal
> buffer object state here.

I remember that I tried to fix this before and you mentioned that it's 
not allowed to hold this lock here. It would possibly deadlock with 
exported buffers. Did this change with Dmitry's rework of the locking 
semantics?

Best regards
Thomas

> 
> Only compile tested!
> 
> Signed-off-by: Christian König <christian.koenig at amd.com>
> Fixes: 43676605f890 drm/ttm: Add vmap/vunmap to TTM and TTM GEM helpers
> ---
>   drivers/gpu/drm/drm_gem_ttm_helper.c | 9 ++++++++-
>   1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_gem_ttm_helper.c b/drivers/gpu/drm/drm_gem_ttm_helper.c
> index d5962a34c01d..e5fc875990c4 100644
> --- a/drivers/gpu/drm/drm_gem_ttm_helper.c
> +++ b/drivers/gpu/drm/drm_gem_ttm_helper.c
> @@ -64,8 +64,13 @@ int drm_gem_ttm_vmap(struct drm_gem_object *gem,
>   		     struct iosys_map *map)
>   {
>   	struct ttm_buffer_object *bo = drm_gem_ttm_of_gem(gem);
> +	int ret;
> +
> +	dma_resv_lock(gem->resv, NULL);
> +	ret = ttm_bo_vmap(bo, map);
> +	dma_resv_unlock(gem->resv);
>   
> -	return ttm_bo_vmap(bo, map);
> +	return ret;
>   }
>   EXPORT_SYMBOL(drm_gem_ttm_vmap);
>   
> @@ -82,7 +87,9 @@ void drm_gem_ttm_vunmap(struct drm_gem_object *gem,
>   {
>   	struct ttm_buffer_object *bo = drm_gem_ttm_of_gem(gem);
>   
> +	dma_resv_lock(gem->resv, NULL);
>   	ttm_bo_vunmap(bo, map);
> +	dma_resv_unlock(gem->resv);
>   }
>   EXPORT_SYMBOL(drm_gem_ttm_vunmap);
>   

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev
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