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

["Christian König" <christian.koenig@amd.com>]

Am 14.11.22 um 00:38 schrieb Dmitry Osipenko:
> 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@google.com>
> Fixes: 79e2cf2e7a19 ("drm/gem: Take reservation lock for vmap/vunmap operations")
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>

Reviewed-by: Christian König <christian.koenig@amd.com

> ---
>   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);
>