Fix device dispatch for linear updater. (#9507)

src/linear/updater_gpu_coordinate.cu

@@ -15,8 +15,7 @@
 #include "../common/timer.h"
 #include "./param.h"
 
-namespace xgboost {
-namespace linear {
+namespace xgboost::linear {
 
 DMLC_REGISTRY_FILE_TAG(updater_gpu_coordinate);
 
@@ -29,7 +28,7 @@ DMLC_REGISTRY_FILE_TAG(updater_gpu_coordinate);
 class GPUCoordinateUpdater : public LinearUpdater {  // NOLINT
  public:
   // set training parameter
-  void Configure(Args const& args) override {
+  void Configure(Args const &args) override {
     tparam_.UpdateAllowUnknown(args);
     coord_param_.UpdateAllowUnknown(args);
     selector_.reset(FeatureSelector::Create(tparam_.feature_selector));
@@ -41,8 +40,9 @@ class GPUCoordinateUpdater : public LinearUpdater {  // NOLINT
     FromJson(config.at("linear_train_param"), &tparam_);
     FromJson(config.at("coordinate_param"), &coord_param_);
   }
-  void SaveConfig(Json* p_out) const override {
-    auto& out = *p_out;
+  void SaveConfig(Json *p_out) const override {
+    LOG(DEBUG) << "Save config for GPU updater.";
+    auto &out = *p_out;
     out["linear_train_param"] = ToJson(tparam_);
     out["coordinate_param"] = ToJson(coord_param_);
   }
@@ -101,10 +101,9 @@ class GPUCoordinateUpdater : public LinearUpdater {  // NOLINT
     monitor_.Stop("LazyInitDevice");
 
     monitor_.Start("UpdateGpair");
-    auto &in_gpair_host = in_gpair->ConstHostVector();
     // Update gpair
     if (ctx_->gpu_id >= 0) {
-      this->UpdateGpair(in_gpair_host);
+      this->UpdateGpair(in_gpair->ConstHostVector());
     }
     monitor_.Stop("UpdateGpair");
 
@@ -249,5 +248,4 @@ XGBOOST_REGISTER_LINEAR_UPDATER(GPUCoordinateUpdater, "gpu_coord_descent")
         "Update linear model according to coordinate descent algorithm. GPU "
         "accelerated.")
     .set_body([]() { return new GPUCoordinateUpdater(); });
-}  // namespace linear
-}  // namespace xgboost
+}  // namespace xgboost::linear