33849792cb
Current NFS clients rely on connection loss to determine when to retransmit. In particular, for protocols like NFSv4, clients no longer rely on RPC timeouts to drive retransmission: NFSv4 servers are required to terminate a connection when they need a client to retransmit pending RPCs. When a server is no longer reachable, either because it has crashed or because the network path has broken, the server cannot actively terminate a connection. Thus NFS clients depend on transport-level keepalive to determine when a connection must be replaced and pending RPCs retransmitted. However, RDMA RC connections do not have a native keepalive mechanism. If an NFS/RDMA server crashes after a client has sent RPCs successfully (an RC ACK has been received for all OTW RDMA requests), there is no way for the client to know the connection is moribund. In addition, new RDMA requests are subject to the RPC-over-RDMA credit limit. If the client has consumed all granted credits with NFS traffic, it is not allowed to send another RDMA request until the server replies. Thus it has no way to send a true keepalive when the workload has already consumed all credits with pending RPCs. To address this, forcibly disconnect a transport when an RPC times out. This prevents moribund connections from stopping the detection of failover or other configuration changes on the server. Note that even if the connection is still good, retransmitting any RPC will trigger a disconnect thanks to this logic in xprt_rdma_send_request: /* Must suppress retransmit to maintain credits */ if (req->rl_connect_cookie == xprt->connect_cookie) goto drop_connection; req->rl_connect_cookie = xprt->connect_cookie; Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.