rpc: share one xps between all backchannels

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.

Cc: stable@vger.kernel.org
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Acked-by: Trond Myklebust <trondmy@primarydata.com>

3 files changed, 17 insertions, 4 deletions

diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index b33721d41adc..2808d550d273 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -452,10 +452,20 @@ static struct rpc_clnt *rpc_create_xprt(struct rpc_create_args *args,
         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))
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index f5572e31d518..4f01f63102ee 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -136,6 +136,8 @@ static void svc_xprt_free(struct kref *kref)
         /* 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);
 }
diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
index 2d3e0c42361e..7e2b2fa189c3 100644
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -3057,6 +3057,7 @@ static struct rpc_xprt *xs_setup_bc_tcp(struct xprt_create *args)
                 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: