Re: [WIP PATCH 05/15] drm/dp_mst: Fix payload deallocation on hotplugs using malloc refs

[Daniel Vetter]

On Thu, Dec 13, 2018 at 08:25:34PM -0500, Lyude Paul wrote:
> Up until now, freeing payloads on remote MST hubs that just had ports
> removed has almost never worked because we've been relying on port
> validation in order to stop us from accessing ports that have already
> been freed from memory, but ports which need their payloads released due
> to being removed will never be a valid part of the topology after
> they've been removed.
> 
> Since we've introduced malloc refs, we can replace all of the validation
> logic in payload helpers which are used for deallocation with some
> well-placed malloc krefs. This ensures that regardless of whether or not
> the ports are still valid and in the topology, any port which has an
> allocated payload will remain allocated in memory until it's payloads
> have been removed - finally allowing us to actually release said
> payloads correctly.
> 
> Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>

I think with this we can also remove the int return value (that everyone
ignored except for some debug output) from drm_dp_update_payload_part1/2.
Follow-up cleanup patch ofc.

This looks good.

Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 54 +++++++++++++++------------
>  1 file changed, 30 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index ae9d019af9f2..93f08bfd2ab3 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -1989,10 +1989,6 @@ static int drm_dp_payload_send_msg(struct drm_dp_mst_topology_mgr *mgr,
>  	u8 sinks[DRM_DP_MAX_SDP_STREAMS];
>  	int i;
>  
> -	port = drm_dp_mst_topology_get_port_validated(mgr, port);
> -	if (!port)
> -		return -EINVAL;
> -
>  	port_num = port->port_num;
>  	mstb = drm_dp_mst_topology_get_mstb_validated(mgr, port->parent);
>  	if (!mstb) {
> @@ -2000,10 +1996,8 @@ static int drm_dp_payload_send_msg(struct drm_dp_mst_topology_mgr *mgr,
>  							       port->parent,
>  							       &port_num);
>  
> -		if (!mstb) {
> -			drm_dp_mst_topology_put_port(port);
> +		if (!mstb)
>  			return -EINVAL;
> -		}
>  	}
>  
>  	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
> @@ -2032,7 +2026,6 @@ static int drm_dp_payload_send_msg(struct drm_dp_mst_topology_mgr *mgr,
>  	kfree(txmsg);
>  fail_put:
>  	drm_dp_mst_topology_put_mstb(mstb);
> -	drm_dp_mst_topology_put_port(port);
>  	return ret;
>  }
>  
> @@ -2137,15 +2130,16 @@ static int drm_dp_destroy_payload_step2(struct drm_dp_mst_topology_mgr *mgr,
>   */
>  int drm_dp_update_payload_part1(struct drm_dp_mst_topology_mgr *mgr)
>  {
> -	int i, j;
> -	int cur_slots = 1;
>  	struct drm_dp_payload req_payload;
>  	struct drm_dp_mst_port *port;
> +	int i, j;
> +	int cur_slots = 1;
>  
>  	mutex_lock(&mgr->payload_lock);
>  	for (i = 0; i < mgr->max_payloads; i++) {
>  		struct drm_dp_vcpi *vcpi = mgr->proposed_vcpis[i];
>  		struct drm_dp_payload *payload = &mgr->payloads[i];
> +		bool put_port = false;
>  
>  		/* solve the current payloads - compare to the hw ones
>  		   - update the hw view */
> @@ -2153,12 +2147,20 @@ int drm_dp_update_payload_part1(struct drm_dp_mst_topology_mgr *mgr)
>  		if (vcpi) {
>  			port = container_of(vcpi, struct drm_dp_mst_port,
>  					    vcpi);
> -			port = drm_dp_mst_topology_get_port_validated(mgr,
> -								      port);
> -			if (!port) {
> -				mutex_unlock(&mgr->payload_lock);
> -				return -EINVAL;
> +
> +			/* Validated ports don't matter if we're releasing
> +			 * VCPI
> +			 */
> +			if (vcpi->num_slots) {
> +				port = drm_dp_mst_topology_get_port_validated(
> +				    mgr, port);
> +				if (!port) {
> +					mutex_unlock(&mgr->payload_lock);
> +					return -EINVAL;
> +				}
> +				put_port = true;
>  			}
> +
>  			req_payload.num_slots = vcpi->num_slots;
>  			req_payload.vcpi = vcpi->vcpi;
>  		} else {
> @@ -2190,7 +2192,7 @@ int drm_dp_update_payload_part1(struct drm_dp_mst_topology_mgr *mgr)
>  		}
>  		cur_slots += req_payload.num_slots;
>  
> -		if (port)
> +		if (put_port)
>  			drm_dp_mst_topology_put_port(port);
>  	}
>  
> @@ -3005,6 +3007,8 @@ bool drm_dp_mst_allocate_vcpi(struct drm_dp_mst_topology_mgr *mgr,
>  	DRM_DEBUG_KMS("initing vcpi for pbn=%d slots=%d\n",
>  		      pbn, port->vcpi.num_slots);
>  
> +	/* Keep port allocated until it's payload has been removed */
> +	drm_dp_mst_get_port_malloc(port);
>  	drm_dp_mst_topology_put_port(port);
>  	return true;
>  out:
> @@ -3034,11 +3038,12 @@ EXPORT_SYMBOL(drm_dp_mst_get_vcpi_slots);
>   */
>  void drm_dp_mst_reset_vcpi_slots(struct drm_dp_mst_topology_mgr *mgr, struct drm_dp_mst_port *port)
>  {
> -	port = drm_dp_mst_topology_get_port_validated(mgr, port);
> -	if (!port)
> -		return;
> +	/*
> +	 * A port with VCPI will remain allocated until it's VCPI is
> +	 * released, no verified ref needed
> +	 */
> +
>  	port->vcpi.num_slots = 0;
> -	drm_dp_mst_topology_put_port(port);
>  }
>  EXPORT_SYMBOL(drm_dp_mst_reset_vcpi_slots);
>  
> @@ -3050,16 +3055,17 @@ EXPORT_SYMBOL(drm_dp_mst_reset_vcpi_slots);
>  void drm_dp_mst_deallocate_vcpi(struct drm_dp_mst_topology_mgr *mgr,
>  				struct drm_dp_mst_port *port)
>  {
> -	port = drm_dp_mst_topology_get_port_validated(mgr, port);
> -	if (!port)
> -		return;
> +	/*
> +	 * A port with VCPI will remain allocated until it's VCPI is
> +	 * released, no verified ref needed
> +	 */
>  
>  	drm_dp_mst_put_payload_id(mgr, port->vcpi.vcpi);
>  	port->vcpi.num_slots = 0;
>  	port->vcpi.pbn = 0;
>  	port->vcpi.aligned_pbn = 0;
>  	port->vcpi.vcpi = 0;
> -	drm_dp_mst_topology_put_port(port);
> +	drm_dp_mst_put_port_malloc(port);
>  }
>  EXPORT_SYMBOL(drm_dp_mst_deallocate_vcpi);
>  
> -- 
> 2.19.2
> 

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