Re: [PATCH 3/3] drm/ttm: remove ttm_bo_wait_unreserved

["Koenig, Christian" <Christian.Koenig@amd.com>]

Am 20.08.19 um 16:53 schrieb Daniel Vetter:
> With nouveau fixed all ttm-using drives have the correct nesting of
> mmap_sem vs dma_resv, and we can just lock the buffer.
>
> Assuming I didn't screw up anything with my audit of course.
>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Christian Koenig <christian.koenig@amd.com>
> Cc: Huang Rui <ray.huang@amd.com>
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Cc: "VMware Graphics" <linux-graphics-maintainer@vmware.com>
> Cc: Thomas Hellstrom <thellstrom@vmware.com>

Yes, please. But one more point: you can now remove bo->wu_mutex as well!

Apart from that Reviewed-by: Christian König <christian.koenig@amd.com>

> ---
>   drivers/gpu/drm/ttm/ttm_bo.c    | 34 ---------------------------------
>   drivers/gpu/drm/ttm/ttm_bo_vm.c | 26 +------------------------
>   include/drm/ttm/ttm_bo_api.h    |  1 -
>   3 files changed, 1 insertion(+), 60 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
> index 20ff56f27aa4..a952dd624b06 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
> @@ -1954,37 +1954,3 @@ void ttm_bo_swapout_all(struct ttm_bo_device *bdev)
>   		;
>   }
>   EXPORT_SYMBOL(ttm_bo_swapout_all);
> -
> -/**
> - * ttm_bo_wait_unreserved - interruptible wait for a buffer object to become
> - * unreserved
> - *
> - * @bo: Pointer to buffer
> - */
> -int ttm_bo_wait_unreserved(struct ttm_buffer_object *bo)
> -{
> -	int ret;
> -
> -	/*
> -	 * In the absense of a wait_unlocked API,
> -	 * Use the bo::wu_mutex to avoid triggering livelocks due to
> -	 * concurrent use of this function. Note that this use of
> -	 * bo::wu_mutex can go away if we change locking order to
> -	 * mmap_sem -> bo::reserve.
> -	 */
> -	ret = mutex_lock_interruptible(&bo->wu_mutex);
> -	if (unlikely(ret != 0))
> -		return -ERESTARTSYS;
> -	if (!dma_resv_is_locked(bo->base.resv))
> -		goto out_unlock;
> -	ret = dma_resv_lock_interruptible(bo->base.resv, NULL);
> -	if (ret == -EINTR)
> -		ret = -ERESTARTSYS;
> -	if (unlikely(ret != 0))
> -		goto out_unlock;
> -	dma_resv_unlock(bo->base.resv);
> -
> -out_unlock:
> -	mutex_unlock(&bo->wu_mutex);
> -	return ret;
> -}
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> index 76eedb963693..505e1787aeea 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> @@ -125,31 +125,7 @@ static vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
>   		&bdev->man[bo->mem.mem_type];
>   	struct vm_area_struct cvma;
>   
> -	/*
> -	 * Work around locking order reversal in fault / nopfn
> -	 * between mmap_sem and bo_reserve: Perform a trylock operation
> -	 * for reserve, and if it fails, retry the fault after waiting
> -	 * for the buffer to become unreserved.
> -	 */
> -	if (unlikely(!dma_resv_trylock(bo->base.resv))) {
> -		if (vmf->flags & FAULT_FLAG_ALLOW_RETRY) {
> -			if (!(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) {
> -				ttm_bo_get(bo);
> -				up_read(&vmf->vma->vm_mm->mmap_sem);
> -				(void) ttm_bo_wait_unreserved(bo);
> -				ttm_bo_put(bo);
> -			}
> -
> -			return VM_FAULT_RETRY;
> -		}
> -
> -		/*
> -		 * If we'd want to change locking order to
> -		 * mmap_sem -> bo::reserve, we'd use a blocking reserve here
> -		 * instead of retrying the fault...
> -		 */
> -		return VM_FAULT_NOPAGE;
> -	}
> +	dma_resv_lock(bo->base.resv, NULL);
>   
>   	/*
>   	 * Refuse to fault imported pages. This should be handled
> diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
> index 43c4929a2171..6b50e624e3e2 100644
> --- a/include/drm/ttm/ttm_bo_api.h
> +++ b/include/drm/ttm/ttm_bo_api.h
> @@ -765,7 +765,6 @@ ssize_t ttm_bo_io(struct ttm_bo_device *bdev, struct file *filp,
>   int ttm_bo_swapout(struct ttm_bo_global *glob,
>   			struct ttm_operation_ctx *ctx);
>   void ttm_bo_swapout_all(struct ttm_bo_device *bdev);
> -int ttm_bo_wait_unreserved(struct ttm_buffer_object *bo);
>   
>   /**
>    * ttm_bo_uses_embedded_gem_object - check if the given bo uses the

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