NFS/RDMA Release resources in svcrdma when device is removed

When removing underlying RDMA device, the rmmod will hang forever if there
are any outstanding NFS/RDMA client mounts. The outstanding NFS/RDMA counts
could also prevent the server from shutting down. Further debugging shows
that the existing connections are not teared down and resource are not
released when receiving RDMA_CM_EVENT_DEVICE_REMOVAL event. It seems the
original code missing svc_xprt_put() in RDMA_CM_EVENT_REMOVAL event handler
thus svc_xprt_free is never invoked to release the existing connection
resources.

The patch has been passed removing, adding device back and forth without
stopping NFS/RDMA service. This will also allow a device to be unplugged
and swapped out without shutting down NFS service.

BugLink: https://bugzilla.linux-nfs.org/show_bug.cgi?id=252Signed-off-by: Shirley Ma <shirley.ma@oracle.com>
Reviewed-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

net/sunrpc/xprtrdma/svc_rdma_transport.c

@@ -659,6 +659,7 @@ static int rdma_cma_handler(struct rdma_cm_id *cma_id,
 		if (xprt) {
 			set_bit(XPT_CLOSE, &xprt->xpt_flags);
 			svc_xprt_enqueue(xprt);
+			svc_xprt_put(xprt);
 		}
 		break;
 	default: