Re: [PATCH 08/10] drm/xe: remove workaround for TTM internals

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On Fri, 2026-07-03 at 18:31 +0200, Natalie Vock wrote:
> From: Christian König <christian.koenig@amd.com>
> 
> This should no longer be necessary, TTM doesn't lock the BO without a
> reference any more.
> 
> Only compile tested!
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>
> Signed-off-by: Natalie Vock <natalie.vock@gmx.de>
> ---
>  drivers/gpu/drm/xe/xe_bo.c | 32 +++++---------------------------
>  1 file changed, 5 insertions(+), 27 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
> index 5843f850339c7..34eae56716076 100644
> --- a/drivers/gpu/drm/xe/xe_bo.c
> +++ b/drivers/gpu/drm/xe/xe_bo.c
> @@ -1642,31 +1642,6 @@ static unsigned long xe_ttm_io_mem_pfn(struct
> ttm_buffer_object *ttm_bo,
>  
>  static void __xe_bo_vunmap(struct xe_bo *bo);
>  
> -/*
> - * TODO: Move this function to TTM so we don't rely on how TTM does
> its
> - * locking, thereby abusing TTM internals.
> - */
> -static bool xe_ttm_bo_lock_in_destructor(struct ttm_buffer_object
> *ttm_bo)
> -{
> -	struct xe_device *xe = ttm_to_xe_device(ttm_bo->bdev);
> -	bool locked;
> -
> -	xe_assert(xe, !kref_read(&ttm_bo->base.refcount));
> -
> -	/*
> -	 * We can typically only race with TTM trylocking under the
> -	 * lru_lock, which will immediately be unlocked again since
> -	 * the ttm_bo refcount is zero at this point. So trylocking
> *should*
> -	 * always succeed here, as long as we hold the lru lock.
> -	 */
> -	spin_lock(&ttm_bo->bdev->lru_lock);
> -	locked = dma_resv_trylock(&ttm_bo->base._resv);
> -	spin_unlock(&ttm_bo->bdev->lru_lock);

We could just remove the spinlocks, update the comment and keep the
asserts. Also the new code below locks .resv rather than ._resv, which
is incorrect for imported dma-bufs.

Thanks,
Thomas


> -	xe_assert(xe, locked);
> -
> -	return locked;
> -}
> -
>  static void xe_ttm_bo_release_notify(struct ttm_buffer_object
> *ttm_bo)
>  {
>  	struct dma_resv_iter cursor;
> @@ -1680,8 +1655,11 @@ static void xe_ttm_bo_release_notify(struct
> ttm_buffer_object *ttm_bo)
>  	bo = ttm_to_xe_bo(ttm_bo);
>  	xe_assert(xe_bo_device(bo), !(bo->created &&
> kref_read(&ttm_bo->base.refcount)));
>  
> -	if (!xe_ttm_bo_lock_in_destructor(ttm_bo))
> -		return;
> +	/*
> +	 * This should never fail since there are no other
> references to the BO
> +	 * any more.
> +	 */
> +	WARN_ON(!dma_resv_trylock(ttm_bo->base.resv));



>  
>  	/*
>  	 * Scrub the preempt fences if any. The unbind fence is
> already