Re: [PATCH 03/10] drm/ttm: do not check if list is empty in ttm_bo_force_list_clean

[Thomas Hellstrom <thellstrom@vmware.com>]

On 11/12/2012 03:00 PM, Maarten Lankhorst wrote:
> Just use the return error from ttm_mem_evict_first instead.

Here driver need to be able to evict a memory type completely, because 
they might shut down
the memory type or clear it for some legacy usage, suspending or 
whatever, so returning 0 on -EBUSY isn't sufficient,
we need at least a list empty check, and a shared reservation at this 
point is illegal.

This is a point where the mechanism to exclude other reservers is 
needed, as we discussed previously.
vmwgfx is using the ttm lock, but will of course adapt if a new 
mechanism is emerging.

Thanks,
/Thomas


>
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
> ---
>   drivers/gpu/drm/ttm/ttm_bo.c | 27 ++++++++-------------------
>   1 file changed, 8 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
> index 74d6e7c..a3383a7 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
> @@ -1302,29 +1302,18 @@ EXPORT_SYMBOL(ttm_bo_create);
>   static int ttm_bo_force_list_clean(struct ttm_bo_device *bdev,
>   					unsigned mem_type, bool allow_errors)
>   {
> -	struct ttm_mem_type_manager *man = &bdev->man[mem_type];
> -	struct ttm_bo_global *glob = bdev->glob;
> -	int ret;
> -
> -	/*
> -	 * Can't use standard list traversal since we're unlocking.
> -	 */
> +	int ret = 0;
>   
> -	spin_lock(&glob->lru_lock);
> -	while (!list_empty(&man->lru)) {
> -		spin_unlock(&glob->lru_lock);
> +	while (!ret) {
>   		ret = ttm_mem_evict_first(bdev, mem_type, false, false, false);
> -		if (ret) {
> -			if (allow_errors) {
> -				return ret;
> -			} else {
> -				pr_err("Cleanup eviction failed\n");
> -			}
> +		if (ret == -EBUSY)
> +			return 0;
> +		else if (ret && !allow_errors) {
> +			pr_err("Cleanup eviction failed\n");
> +			ret = 0;
>   		}
> -		spin_lock(&glob->lru_lock);
>   	}
> -	spin_unlock(&glob->lru_lock);
> -	return 0;
> +	return ret;
>   }
>   
>   int ttm_bo_clean_mm(struct ttm_bo_device *bdev, unsigned mem_type)