nfs: fixed broken compilation in nfs_callback_up_net()

Patch fixes compilation error in nfs_callback_up_net()
serv->sv_bc_enabled is defined under enabled CONFIG_SUNRPC_BACKCHANNEL,
however nfs_callback_up_net() can access it even if this config option
was not set.

Fixes: a289ce53 (sunrpc: replace svc_serv->sv_bc_xprt by boolean flag)
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfs/callback.c

@@ -210,7 +210,7 @@ static int nfs_callback_up_net(int minorversion, struct svc_serv *serv,
 	if (!IS_ENABLED(CONFIG_NFS_V4_1) || minorversion == 0)
 		ret = nfs4_callback_up_net(serv, net);
 	else if (xprt->ops->bc_setup)
-		serv->sv_bc_enabled = true;
+		set_bc_enabled(serv);
 	else
 		ret = -EPROTONOSUPPORT;
 

include/linux/sunrpc/bc_xprt.h

@@ -51,6 +51,11 @@ static inline bool svc_is_backchannel(const struct svc_rqst *rqstp)
 {
 	return rqstp->rq_server->sv_bc_enabled;
 }
+
+static inline void set_bc_enabled(struct svc_serv *serv)
+{
+	serv->sv_bc_enabled = true;
+}
 #else /* CONFIG_SUNRPC_BACKCHANNEL */
 static inline int xprt_setup_backchannel(struct rpc_xprt *xprt,
 					 unsigned int min_reqs)
@@ -63,6 +68,10 @@ static inline bool svc_is_backchannel(const struct svc_rqst *rqstp)
 	return false;
 }
 
+static inline void set_bc_enabled(struct svc_serv *serv)
+{
+}
+
 static inline void xprt_free_bc_request(struct rpc_rqst *req)
 {
 }