RDMA: Add rdma_connect_locked()

There are two flows for handling RDMA_CM_EVENT_ROUTE_RESOLVED, either the
handler triggers a completion and another thread does rdma_connect() or
the handler directly calls rdma_connect().

In all cases rdma_connect() needs to hold the handler_mutex, but when
handler's are invoked this is already held by the core code. This causes
ULPs using the 2nd method to deadlock.

Provide a rdma_connect_locked() and have all ULPs call it from their
handlers.

Link: https://lore.kernel.org/r/0-v2-53c22d5c1405+33-rdma_connect_locking_jgg@nvidia.com
Reported-and-tested-by: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
Fixes: 2a7cec5381 ("RDMA/cma: Fix locking for the RDMA_CM_CONNECT state")
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Acked-by: Jack Wang <jinpu.wang@cloud.ionos.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Max Gurtovoy <mgurtovoy@nvidia.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

include/rdma/rdma_cm.h

@@ -227,19 +227,9 @@ void rdma_destroy_qp(struct rdma_cm_id *id);
 int rdma_init_qp_attr(struct rdma_cm_id *id, struct ib_qp_attr *qp_attr,
 		       int *qp_attr_mask);
 
-/**
- * rdma_connect - Initiate an active connection request.
- * @id: Connection identifier to connect.
- * @conn_param: Connection information used for connected QPs.
- *
- * Users must have resolved a route for the rdma_cm_id to connect with
- * by having called rdma_resolve_route before calling this routine.
- *
- * This call will either connect to a remote QP or obtain remote QP
- * information for unconnected rdma_cm_id's.  The actual operation is
- * based on the rdma_cm_id's port space.
- */
 int rdma_connect(struct rdma_cm_id *id, struct rdma_conn_param *conn_param);
+int rdma_connect_locked(struct rdma_cm_id *id,
+			struct rdma_conn_param *conn_param);
 
 int rdma_connect_ece(struct rdma_cm_id *id, struct rdma_conn_param *conn_param,
 		     struct rdma_ucm_ece *ece);