Re: [PATCH] drm/ttm: remove ttm_bo_wait_unreserved

From: "Thomas Hellström (VMware)" <thomas_os@shipmail.org>
To: dri-devel@lists.freedesktop.org
Subject: Re: [PATCH] drm/ttm: remove ttm_bo_wait_unreserved
Date: Wed, 21 Aug 2019 17:39:36 +0200	[thread overview]
Message-ID: <0f74b20f-d3a3-cca9-9f67-0bb14faa7f3c@shipmail.org> (raw)
In-Reply-To: <20190821153352.4705-1-daniel.vetter@ffwll.ch>

On 8/21/19 5:33 PM, 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)
>
> Reviewed-by: Christian König <christian.koenig@amd.com>
> 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>
> ---
>   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 20ff56f27aa4..d1ce5d315d5b 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
> @@ -162,7 +162,6 @@ 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(bdev->glob->mem_glob, acc_size);
>   }
> @@ -1319,7 +1318,6 @@ 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;
> @@ -1954,37 +1952,3 @@ 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_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
> index fe81c565e7ef..82ea26a49959 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_util.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
> @@ -508,7 +508,6 @@ 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);
>   	atomic_set(&fbo->base.cpu_writers, 0);
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> index 76eedb963693..a61a35e57d1c 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> @@ -125,30 +125,22 @@ 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);
> +				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;
>   	}
>   
>   	/*
> diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
> index 43c4929a2171..21c7d0d28757 100644
> --- a/include/drm/ttm/ttm_bo_api.h
> +++ b/include/drm/ttm/ttm_bo_api.h
> @@ -155,7 +155,6 @@ 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
> @@ -229,8 +228,6 @@ struct ttm_buffer_object {
>   	uint64_t offset; /* GPU address space is independent of CPU word size */
>   
>   	struct sg_table *sg;
> -
> -	struct mutex wu_mutex;
>   };
>   
>   /**
> @@ -765,7 +762,6 @@ 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

Thanks. LGTM.

Reviewed-by: Thomas Hellström <thellstrom@vmware.com>

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