[Intel-gfx] [PATCH 3/3] drm/dp/mst: Track available time slots in DP Multi-Stream Transport Packet

[Chris Wilson]

On Thu, Nov 17, 2016 at 06:03:48PM -0800, Dhinakaran Pandiyan wrote:
>  static int drm_dp_init_vcpi(struct drm_dp_mst_topology_mgr *mgr,
>  			    struct drm_dp_vcpi *vcpi, int pbn)
>  {
> -	int num_slots;
> +	int req_slots;
>  	int ret;
>  
> -	num_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
> +	req_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
>  
> -	if (num_slots > mgr->avail_slots)
> -		return -ENOSPC;
> +	mutex_lock(&mgr->lock);
> +	if (req_slots > mgr->avail_slots) {
> +		ret = -ENOSPC;
> +		goto out;
> +	}

You are not atomically reducing the mgr->avail_slots, leading to
possible overallocation of multiple streams?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre