FAILED: patch "[PATCH] xprtrdma: Reset credit grant properly after a disconnect" failed to apply to 4.14-stable tree

The patch below does not apply to the 4.14-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From: Chuck Lever <[email protected]>
Date: Mon, 1 Oct 2018 14:25:14 -0400
Subject: [PATCH] xprtrdma: Reset credit grant properly after a disconnect

On a fresh connection, an RPC/RDMA client is supposed to send only one RPC Call until it gets a credit grant in the first RPC Reply from the server [RFC 8166, Section 3.3.3].

There is a bug in the Linux client's credit accounting mechanism introduced by commit e7ce710a8802 ("xprtrdma: Avoid deadlock when credit window is reset"). On connect, it simply dumps all pending RPC Calls onto the new connection.

Servers have been tolerant of this bad behavior. Currently no server implementation ever changes its credit grant over reconnects, and servers always repost enough Receives before connections are fully established.

To correct this issue, ensure that the client resets both the credit grant _and_ the congestion window when handling a reconnect.

index a68180090554..b9827665ff35 100644
@@ -248,6 +248,7 @@ static void
 xprt_rdma_bc_close(struct rpc_xprt *xprt)
 {
 	dprintk("svcrdma: %s: xprt %p\n", __func__, xprt);
+	xprt->cwnd = RPC_CWNDSHIFT;
 }
 
 static void

index 143ce2579ba9..98cbc7b060ba 100644
@@ -468,6 +468,12 @@ xprt_rdma_close(struct rpc_xprt *xprt)
 		xprt->reestablish_timeout = 0;
 	xprt_disconnect_done(xprt);
 	rpcrdma_ep_disconnect(ep, ia);
+
+	/* Prepare @xprt for the next connection by reinitializing
+	 * its credit grant to one (see RFC 8166, Section 3.3.3).
+	 */
+	r_xprt->rx_buf.rb_credits = 1;
+	xprt->cwnd = RPC_CWNDSHIFT;
 }
 
 /**