Re: [PATCH] drm/ttm: remove ttm_bo_wait_unreserved

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

Am 22.08.19 um 15:06 schrieb Daniel Vetter:
> On Thu, Aug 22, 2019 at 07:56:56AM +0000, Koenig, Christian wrote:
>> Am 22.08.19 um 08:49 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.
>>>
>>> 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>
> btw I realized I didn't remove your r-b, since v1 was broken.
>
> For formality, can you pls reaffirm, or still something broken?

My r-b is still valid.

Only problem I see is that neither of us seems to have a good idea about 
the different VM_FAULT_* replies.

But that worked before so it should still work now,
Christian.

>
> Also from the other thread: Reviewed-by: Thomas Hellström <thellstrom@vmware.com>
>
> Thanks, Daniel
>
>>> 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)) {
>> Not an expert on fault handling, but shouldn't this now be one if?
>>
>> E.g. if FAULT_FLAG_RETRY_NOWAIT is set we should return VM_FAULT_NOPAGE
>> instead of VM_FAULT_RETRY.
>>
>> But really take that with a grain of salt,
>> Christian.
>>
>>>    				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

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