[PATCH 4.6 057/203] rpc: share one xps between all backchannels

[Greg Kroah-Hartman]

4.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: J. Bruce Fields <bfields@xxxxxxxxxx>

commit 39a9beab5acb83176e8b9a4f0778749a09341f1f upstream.

The spec allows backchannels for multiple clients to share the same tcp
connection.  When that happens, we need to use the same xprt for all of
them.  Similarly, we need the same xps.

This fixes list corruption introduced by the multipath code.

Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
Acked-by: Trond Myklebust <trondmy@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 include/linux/sunrpc/svc_xprt.h |    1 +
 include/linux/sunrpc/xprt.h     |    1 +
 net/sunrpc/clnt.c               |   18 ++++++++++++++----
 net/sunrpc/svc_xprt.c           |    2 ++
 net/sunrpc/xprtsock.c           |    1 +
 5 files changed, 19 insertions(+), 4 deletions(-)

--- a/include/linux/sunrpc/svc_xprt.h
+++ b/include/linux/sunrpc/svc_xprt.h
@@ -84,6 +84,7 @@ struct svc_xprt {
 
 	struct net		*xpt_net;
 	struct rpc_xprt		*xpt_bc_xprt;	/* NFSv4.1 backchannel */
+	struct rpc_xprt_switch	*xpt_bc_xps;	/* NFSv4.1 backchannel */
 };
 
 static inline void unregister_xpt_user(struct svc_xprt *xpt, struct svc_xpt_user *u)
--- a/include/linux/sunrpc/xprt.h
+++ b/include/linux/sunrpc/xprt.h
@@ -296,6 +296,7 @@ struct xprt_create {
 	size_t			addrlen;
 	const char		*servername;
 	struct svc_xprt		*bc_xprt;	/* NFSv4.1 backchannel */
+	struct rpc_xprt_switch	*bc_xps;
 	unsigned int		flags;
 };
 
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -452,10 +452,20 @@ static struct rpc_clnt *rpc_create_xprt(
 	struct rpc_clnt *clnt = NULL;
 	struct rpc_xprt_switch *xps;
 
-	xps = xprt_switch_alloc(xprt, GFP_KERNEL);
-	if (xps == NULL) {
-		xprt_put(xprt);
-		return ERR_PTR(-ENOMEM);
+	if (args->bc_xprt && args->bc_xprt->xpt_bc_xps) {
+		WARN_ON(args->protocol != XPRT_TRANSPORT_BC_TCP);
+		xps = args->bc_xprt->xpt_bc_xps;
+		xprt_switch_get(xps);
+	} else {
+		xps = xprt_switch_alloc(xprt, GFP_KERNEL);
+		if (xps == NULL) {
+			xprt_put(xprt);
+			return ERR_PTR(-ENOMEM);
+		}
+		if (xprt->bc_xprt) {
+			xprt_switch_get(xps);
+			xprt->bc_xprt->xpt_bc_xps = xps;
+		}
 	}
 	clnt = rpc_new_client(args, xps, xprt, NULL);
 	if (IS_ERR(clnt))
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -136,6 +136,8 @@ static void svc_xprt_free(struct kref *k
 	/* See comment on corresponding get in xs_setup_bc_tcp(): */
 	if (xprt->xpt_bc_xprt)
 		xprt_put(xprt->xpt_bc_xprt);
+	if (xprt->xpt_bc_xps)
+		xprt_switch_put(xprt->xpt_bc_xps);
 	xprt->xpt_ops->xpo_free(xprt);
 	module_put(owner);
 }
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -3050,6 +3050,7 @@ static struct rpc_xprt *xs_setup_bc_tcp(
 		return xprt;
 
 	args->bc_xprt->xpt_bc_xprt = NULL;
+	args->bc_xprt->xpt_bc_xps = NULL;
 	xprt_put(xprt);
 	ret = ERR_PTR(-EINVAL);
 out_err: