RDMA/restrack: Release task struct which was hold by CM_ID object

Tracking CM_ID resource is performed in two stages: creation of cm_id
and connecting it to the cma_dev. It is needed because rdma-cm protocol
exports two separate user-visible calls rdma_create_id and rdma_accept.

At the time of CM_ID creation, the real owner of that object is unknown
yet and we need to grab task_struct. This task_struct is released or
reassigned in attach phase later on. but call to rdma_destroy_id left
this task_struct unreleased.

Such separation is unique to CM_ID and other restrack objects initialize
in one shot. It means that it is safe to use "res->valid" check to catch
unfinished CM_ID flow and release task_struct for that object.

Fixes: 00313983 ("RDMA/nldev: provide detailed CM_ID information")
Reported-by: Artemy Kovalyov <artemyko@mellanox.com>
Reviewed-by: Artemy Kovalyov <artemyko@mellanox.com>
Reviewed-by: Yossi Itigin <yosefe@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/core/cma.c

@@ -1815,8 +1815,8 @@ void rdma_destroy_id(struct rdma_cm_id *id)
 	mutex_lock(&id_priv->handler_mutex);
 	mutex_unlock(&id_priv->handler_mutex);
 
-	if (id_priv->cma_dev) {
 	rdma_restrack_del(&id_priv->res);
+	if (id_priv->cma_dev) {
 		if (rdma_cap_ib_cm(id_priv->id.device, 1)) {
 			if (id_priv->cm_id.ib)
 				ib_destroy_cm_id(id_priv->cm_id.ib);
@@ -3542,10 +3542,9 @@ int rdma_bind_addr(struct rdma_cm_id *id, struct sockaddr *addr)
 
 	return 0;
 err2:
-	if (id_priv->cma_dev) {
 	rdma_restrack_del(&id_priv->res);
+	if (id_priv->cma_dev)
 		cma_release_dev(id_priv);
-	}
 err1:
 	cma_comp_exch(id_priv, RDMA_CM_ADDR_BOUND, RDMA_CM_IDLE);
 	return ret;

drivers/infiniband/core/restrack.c

@@ -223,7 +223,7 @@ void rdma_restrack_del(struct rdma_restrack_entry *res)
 	struct ib_device *dev;
 
 	if (!res->valid)
-		return;
+		goto out;
 
 	dev = res_to_dev(res);
 	if (!dev)
@@ -236,8 +236,10 @@ void rdma_restrack_del(struct rdma_restrack_entry *res)
 	down_write(&dev->res.rwsem);
 	hash_del(&res->node);
 	res->valid = false;
+	up_write(&dev->res.rwsem);
+
+out:
 	if (res->task)
 		put_task_struct(res->task);
-	up_write(&dev->res.rwsem);
 }
 EXPORT_SYMBOL(rdma_restrack_del);