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

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Nov 04, 2019 at 06:38:01PM +0100, Daniel Vetter wrote:
> 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.
> 
> v2:
> - Dont forget wu_mutex (Christian König)
> - Keep the mmap_sem-less wait optimization (Thomas)
> - Use _lock_interruptible to be good citizens (Thomas)
> 
> v3: Rebase over fault handler helperification.
> 
> Reviewed-by: Christian König <christian.koenig@amd.com> (v2)
> Reviewed-by: Thomas Hellström <thellstrom@vmware.com> (v2)
> 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>

Entire series merged into drm-misc-next (probably for 5.6) with Dave's
irc-ack for the nouveau patch.
-Daniel

> ---
>  drivers/gpu/drm/ttm/ttm_bo.c      | 36 -------------------------------
>  drivers/gpu/drm/ttm/ttm_bo_util.c |  1 -
>  drivers/gpu/drm/ttm/ttm_bo_vm.c   | 18 +++++-----------
>  include/drm/ttm/ttm_bo_api.h      |  4 ----
>  4 files changed, 5 insertions(+), 54 deletions(-)
> 
> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
> index 8d91b0428af1..5df596fb0280 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
> @@ -161,7 +161,6 @@ static void ttm_bo_release_list(struct kref *list_kref)
>  	dma_fence_put(bo->moving);
>  	if (!ttm_bo_uses_embedded_gem_object(bo))
>  		dma_resv_fini(&bo->base._resv);
> -	mutex_destroy(&bo->wu_mutex);
>  	bo->destroy(bo);
>  	ttm_mem_global_free(&ttm_mem_glob, acc_size);
>  }
> @@ -1299,7 +1298,6 @@ int ttm_bo_init_reserved(struct ttm_bo_device *bdev,
>  	INIT_LIST_HEAD(&bo->ddestroy);
>  	INIT_LIST_HEAD(&bo->swap);
>  	INIT_LIST_HEAD(&bo->io_reserve_lru);
> -	mutex_init(&bo->wu_mutex);
>  	bo->bdev = bdev;
>  	bo->type = type;
>  	bo->num_pages = num_pages;
> @@ -1903,37 +1901,3 @@ void ttm_bo_swapout_all(struct ttm_bo_device *bdev)
>  	while (ttm_bo_swapout(&ttm_bo_glob, &ctx) == 0);
>  }
>  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_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
> index 6b0883a1776e..2b0e5a088da0 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_util.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
> @@ -504,7 +504,6 @@ static int ttm_buffer_object_transfer(struct ttm_buffer_object *bo,
>  	INIT_LIST_HEAD(&fbo->base.lru);
>  	INIT_LIST_HEAD(&fbo->base.swap);
>  	INIT_LIST_HEAD(&fbo->base.io_reserve_lru);
> -	mutex_init(&fbo->base.wu_mutex);
>  	fbo->base.moving = NULL;
>  	drm_vma_node_reset(&fbo->base.base.vma_node);
>  
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> index 11863fbdd5d6..91466cfb6f16 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> @@ -128,30 +128,22 @@ static unsigned long ttm_bo_io_mem_pfn(struct ttm_buffer_object *bo,
>  vm_fault_t ttm_bo_vm_reserve(struct ttm_buffer_object *bo,
>  			     struct vm_fault *vmf)
>  {
> -	/*
> -	 * 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);
> +				if (!dma_resv_lock_interruptible(bo->base.resv,
> +								 NULL))
> +					dma_resv_unlock(bo->base.resv);
>  				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;
> +		if (dma_resv_lock_interruptible(bo->base.resv, NULL))
> +			return VM_FAULT_NOPAGE;
>  	}
>  
>  	return 0;
> diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
> index 65e399d280f7..e8b0f0c66059 100644
> --- a/include/drm/ttm/ttm_bo_api.h
> +++ b/include/drm/ttm/ttm_bo_api.h
> @@ -154,7 +154,6 @@ struct ttm_tt;
>   * @offset: The current GPU offset, which can have different meanings
>   * depending on the memory type. For SYSTEM type memory, it should be 0.
>   * @cur_placement: Hint of current placement.
> - * @wu_mutex: Wait unreserved mutex.
>   *
>   * Base class for TTM buffer object, that deals with data placement and CPU
>   * mappings. GPU mappings are really up to the driver, but for simpler GPUs
> @@ -222,8 +221,6 @@ struct ttm_buffer_object {
>  	uint64_t offset; /* GPU address space is independent of CPU word size */
>  
>  	struct sg_table *sg;
> -
> -	struct mutex wu_mutex;
>  };
>  
>  /**
> @@ -707,7 +704,6 @@ 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
> -- 
> 2.24.0.rc2
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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