xprtrdma: Reset credit grant properly after a disconnect

chucklever · amschuma-ntap · commit ef739b2175dd · 2018-10-02T15:45:09.000-04:00
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 e7ce710 ("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. Fixes: e7ce710 ("xprtrdma: Avoid deadlock when credit ... ") Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Cc: stable@kernel.org Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
diff --git a/net/sunrpc/xprtrdma/svc_rdma_backchannel.c b/net/sunrpc/xprtrdma/svc_rdma_backchannel.c
@@ -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
diff --git a/net/sunrpc/xprtrdma/transport.c b/net/sunrpc/xprtrdma/transport.c
@@ -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;
 }
 
 /**

Original file line number	Diff line number	Diff line change
`@@ -248,6 +248,7 @@ static void`
`248`	`248`	`xprt_rdma_bc_close(struct rpc_xprt *xprt)`
`249`	`249`	`{`
`250`	`250`	`dprintk("svcrdma: %s: xprt %p\n", __func__, xprt);`
	`251`	`+ xprt->cwnd = RPC_CWNDSHIFT;`
`251`	`252`	`}`
`252`	`253`
`253`	`254`	`static void`