Re: [PATCH v1] drm/gem-vram: Fix deadlock in drm_gem_vram_vmap()

[Dmitry Osipenko]

On 11/14/22 02:38, Dmitry Osipenko wrote:
> Recently DRM framebuffer core and all drivers were moved to unlocked
> vmapping functions that take the reservation lock. The drm_gem_vram_vmap()
> was missed out by accident and now deadlocks drivers that use drm_gem_vram
> helpers when framebuffer is updated, like Bochs driver. Remove the locking
> from drm_gem_vram_v[un]map() functions to fix the deadlock.
> 
> Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Fixes: 79e2cf2e7a19 ("drm/gem: Take reservation lock for vmap/vunmap operations")
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>
> ---
>  drivers/gpu/drm/drm_gem_vram_helper.c | 18 +++---------------
>  1 file changed, 3 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gem_vram_helper.c b/drivers/gpu/drm/drm_gem_vram_helper.c
> index 125160b534be..b6c7e3803bb3 100644
> --- a/drivers/gpu/drm/drm_gem_vram_helper.c
> +++ b/drivers/gpu/drm/drm_gem_vram_helper.c
> @@ -433,25 +433,19 @@ int drm_gem_vram_vmap(struct drm_gem_vram_object *gbo, struct iosys_map *map)
>  {
>  	int ret;
>  
> -	ret = ttm_bo_reserve(&gbo->bo, true, false, NULL);
> -	if (ret)
> -		return ret;
> +	dma_resv_assert_held(gbo->bo.base.resv);
>  
>  	ret = drm_gem_vram_pin_locked(gbo, 0);
>  	if (ret)
> -		goto err_ttm_bo_unreserve;
> +		return ret;
>  	ret = drm_gem_vram_kmap_locked(gbo, map);
>  	if (ret)
>  		goto err_drm_gem_vram_unpin_locked;
>  
> -	ttm_bo_unreserve(&gbo->bo);
> -
>  	return 0;
>  
>  err_drm_gem_vram_unpin_locked:
>  	drm_gem_vram_unpin_locked(gbo);
> -err_ttm_bo_unreserve:
> -	ttm_bo_unreserve(&gbo->bo);
>  	return ret;
>  }
>  EXPORT_SYMBOL(drm_gem_vram_vmap);
> @@ -467,16 +461,10 @@ EXPORT_SYMBOL(drm_gem_vram_vmap);
>  void drm_gem_vram_vunmap(struct drm_gem_vram_object *gbo,
>  			 struct iosys_map *map)
>  {
> -	int ret;
> -
> -	ret = ttm_bo_reserve(&gbo->bo, false, false, NULL);
> -	if (WARN_ONCE(ret, "ttm_bo_reserve_failed(): ret=%d\n", ret))
> -		return;
> +	dma_resv_assert_held(gbo->bo.base.resv);
>  
>  	drm_gem_vram_kunmap_locked(gbo, map);
>  	drm_gem_vram_unpin_locked(gbo);
> -
> -	ttm_bo_unreserve(&gbo->bo);
>  }
>  EXPORT_SYMBOL(drm_gem_vram_vunmap);
>  

Applied to drm-misc-next

-- 
Best regards,
Dmitry