diff --git a/CMakeLists.txt b/CMakeLists.txt
index e2c906869..72d612d18 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,9 +1,10 @@
 cmake_minimum_required(VERSION 3.13)
-project(xgboost LANGUAGES CXX C VERSION 1.2.0)
+project(xgboost LANGUAGES CXX C VERSION 1.2.1)
 include(cmake/Utils.cmake)
 list(APPEND CMAKE_MODULE_PATH "${xgboost_SOURCE_DIR}/cmake/modules")
 cmake_policy(SET CMP0022 NEW)
 cmake_policy(SET CMP0079 NEW)
+set(CMAKE_POLICY_DEFAULT_CMP0063 NEW)
 cmake_policy(SET CMP0063 NEW)
 
 if ((${CMAKE_VERSION} VERSION_GREATER 3.13) OR (${CMAKE_VERSION} VERSION_EQUAL 3.13))
@@ -173,9 +174,6 @@ foreach(lib rabit rabit_base rabit_empty rabit_mock rabit_mock_static)
   # from dmlc is correctly applied to rabit.
   if (TARGET ${lib})
     target_link_libraries(${lib} dmlc ${CMAKE_THREAD_LIBS_INIT})
-    if (HIDE_CXX_SYMBOLS)  # Hide all C++ symbols from Rabit
-      set_target_properties(${lib} PROPERTIES CXX_VISIBILITY_PRESET hidden)
-    endif (HIDE_CXX_SYMBOLS)
     if (ENABLE_ALL_WARNINGS)
       target_compile_options(${lib} PRIVATE -Wall -Wextra)
     endif (ENABLE_ALL_WARNINGS)
@@ -204,8 +202,9 @@ endif (USE_NVTX)
 
 #-- Hide all C++ symbols
 if (HIDE_CXX_SYMBOLS)
-  set_target_properties(objxgboost PROPERTIES CXX_VISIBILITY_PRESET hidden)
-  set_target_properties(xgboost PROPERTIES CXX_VISIBILITY_PRESET hidden)
+  foreach(target objxgboost xgboost dmlc rabit rabit_mock_static)
+    set_target_properties(${target} PROPERTIES CXX_VISIBILITY_PRESET hidden)
+  endforeach()
 endif (HIDE_CXX_SYMBOLS)
 
 target_include_directories(xgboost
diff --git a/Jenkinsfile b/Jenkinsfile
index 245b1309b..8b1e4452a 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -144,7 +144,7 @@ def ClangTidy() {
     echo "Running clang-tidy job..."
     def container_type = "clang_tidy"
     def docker_binary = "docker"
-    def dockerArgs = "--build-arg CUDA_VERSION=10.1"
+    def dockerArgs = "--build-arg CUDA_VERSION_ARG=10.1"
     sh """
     ${dockerRun} ${container_type} ${docker_binary} ${dockerArgs} python3 tests/ci_build/tidy.py
     """
@@ -261,7 +261,7 @@ def BuildCUDA(args) {
     echo "Build with CUDA ${args.cuda_version}"
     def container_type = GetCUDABuildContainerType(args.cuda_version)
     def docker_binary = "docker"
-    def docker_args = "--build-arg CUDA_VERSION=${args.cuda_version}"
+    def docker_args = "--build-arg CUDA_VERSION_ARG=${args.cuda_version}"
     def arch_flag = ""
     if (env.BRANCH_NAME != 'master' && !(env.BRANCH_NAME.startsWith('release'))) {
       arch_flag = "-DGPU_COMPUTE_VER=75"
@@ -290,7 +290,7 @@ def BuildJVMPackagesWithCUDA(args) {
     echo "Build XGBoost4J-Spark with Spark ${args.spark_version}, CUDA ${args.cuda_version}"
     def container_type = "jvm_gpu_build"
     def docker_binary = "nvidia-docker"
-    def docker_args = "--build-arg CUDA_VERSION=${args.cuda_version}"
+    def docker_args = "--build-arg CUDA_VERSION_ARG=${args.cuda_version}"
     def arch_flag = ""
     if (env.BRANCH_NAME != 'master' && !(env.BRANCH_NAME.startsWith('release'))) {
       arch_flag = "-DGPU_COMPUTE_VER=75"
@@ -365,7 +365,7 @@ def TestPythonGPU(args) {
     echo "Test Python GPU: CUDA ${args.host_cuda_version}"
     def container_type = "gpu"
     def docker_binary = "nvidia-docker"
-    def docker_args = "--build-arg CUDA_VERSION=${args.host_cuda_version}"
+    def docker_args = "--build-arg CUDA_VERSION_ARG=${args.host_cuda_version}"
     if (args.multi_gpu) {
       echo "Using multiple GPUs"
       // Allocate extra space in /dev/shm to enable NCCL
@@ -406,7 +406,7 @@ def TestCppGPU(args) {
     echo "Test C++, CUDA ${args.host_cuda_version}"
     def container_type = "gpu"
     def docker_binary = "nvidia-docker"
-    def docker_args = "--build-arg CUDA_VERSION=${args.host_cuda_version}"
+    def docker_args = "--build-arg CUDA_VERSION_ARG=${args.host_cuda_version}"
     sh "${dockerRun} ${container_type} ${docker_binary} ${docker_args} build/testxgboost"
     deleteDir()
   }
@@ -424,7 +424,7 @@ def CrossTestJVMwithJDKGPU(args) {
     }
     def container_type = "gpu_jvm"
     def docker_binary = "nvidia-docker"
-    def docker_args = "--build-arg CUDA_VERSION=${args.host_cuda_version}"
+    def docker_args = "--build-arg CUDA_VERSION_ARG=${args.host_cuda_version}"
     sh "${dockerRun} ${container_type} ${docker_binary} ${docker_args} tests/ci_build/test_jvm_gpu_cross.sh"
     deleteDir()
   }
@@ -476,7 +476,7 @@ def DeployJVMPackages(args) {
       ${dockerRun} jvm docker tests/ci_build/deploy_jvm_packages.sh ${args.spark_version} 0
       """
       sh """
-      ${dockerRun} jvm_gpu_build docker --build-arg CUDA_VERSION=10.0 tests/ci_build/deploy_jvm_packages.sh ${args.spark_version} 1
+      ${dockerRun} jvm_gpu_build docker --build-arg CUDA_VERSION_ARG=10.0 tests/ci_build/deploy_jvm_packages.sh ${args.spark_version} 1
       """
     }
     deleteDir()
diff --git a/python-package/xgboost/VERSION b/python-package/xgboost/VERSION
index 26aaba0e8..6085e9465 100644
--- a/python-package/xgboost/VERSION
+++ b/python-package/xgboost/VERSION
@@ -1 +1 @@
-1.2.0
+1.2.1
diff --git a/python-package/xgboost/core.py b/python-package/xgboost/core.py
index 4bc77783e..76e78a809 100644
--- a/python-package/xgboost/core.py
+++ b/python-package/xgboost/core.py
@@ -40,7 +40,7 @@ class EarlyStopException(Exception):
     """
 
     def __init__(self, best_iteration):
-        super(EarlyStopException, self).__init__()
+        super().__init__()
         self.best_iteration = best_iteration
 
 
diff --git a/python-package/xgboost/sklearn.py b/python-package/xgboost/sklearn.py
index d1c3c6d53..1312d57b4 100644
--- a/python-package/xgboost/sklearn.py
+++ b/python-package/xgboost/sklearn.py
@@ -1017,7 +1017,7 @@ class XGBRFClassifier(XGBClassifier):
                          **kwargs)
 
     def get_xgb_params(self):
-        params = super(XGBRFClassifier, self).get_xgb_params()
+        params = super().get_xgb_params()
         params['num_parallel_tree'] = self.n_estimators
         return params
 
@@ -1049,7 +1049,7 @@ class XGBRFRegressor(XGBRegressor):
                          reg_lambda=reg_lambda, **kwargs)
 
     def get_xgb_params(self):
-        params = super(XGBRFRegressor, self).get_xgb_params()
+        params = super().get_xgb_params()
         params['num_parallel_tree'] = self.n_estimators
         return params
 
diff --git a/tests/ci_build/Dockerfile.clang_tidy b/tests/ci_build/Dockerfile.clang_tidy
index 2316feda1..661e9b925 100644
--- a/tests/ci_build/Dockerfile.clang_tidy
+++ b/tests/ci_build/Dockerfile.clang_tidy
@@ -1,5 +1,6 @@
-ARG CUDA_VERSION
-FROM nvidia/cuda:$CUDA_VERSION-devel-ubuntu18.04
+ARG CUDA_VERSION_ARG
+FROM nvidia/cuda:$CUDA_VERSION_ARG-devel-ubuntu18.04
+ARG CUDA_VERSION_ARG
 
 # Environment
 ENV DEBIAN_FRONTEND noninteractive
diff --git a/tests/ci_build/Dockerfile.gpu b/tests/ci_build/Dockerfile.gpu
index ca754503e..211f150dc 100644
--- a/tests/ci_build/Dockerfile.gpu
+++ b/tests/ci_build/Dockerfile.gpu
@@ -1,5 +1,6 @@
-ARG CUDA_VERSION
-FROM nvidia/cuda:$CUDA_VERSION-runtime-ubuntu16.04
+ARG CUDA_VERSION_ARG
+FROM nvidia/cuda:$CUDA_VERSION_ARG-runtime-ubuntu16.04
+ARG CUDA_VERSION_ARG
 
 # Environment
 ENV DEBIAN_FRONTEND noninteractive
@@ -18,7 +19,7 @@ ENV PATH=/opt/python/bin:$PATH
 # Create new Conda environment with cuDF, Dask, and cuPy
 RUN \
     conda create -n gpu_test -c rapidsai-nightly -c rapidsai -c nvidia -c conda-forge -c defaults \
-        python=3.7 cudf=0.15* cudatoolkit=$CUDA_VERSION dask dask-cuda dask-cudf cupy \
+        python=3.7 cudf=0.15* cudatoolkit=$CUDA_VERSION_ARG dask dask-cuda dask-cudf cupy \
         numpy pytest scipy scikit-learn pandas matplotlib wheel python-kubernetes urllib3 graphviz hypothesis
 
 ENV GOSU_VERSION 1.10
diff --git a/tests/ci_build/Dockerfile.gpu_build b/tests/ci_build/Dockerfile.gpu_build
index 8a741fc87..a52e62eb3 100644
--- a/tests/ci_build/Dockerfile.gpu_build
+++ b/tests/ci_build/Dockerfile.gpu_build
@@ -1,6 +1,6 @@
-ARG CUDA_VERSION
-FROM nvidia/cuda:$CUDA_VERSION-devel-ubuntu16.04
-ARG CUDA_VERSION
+ARG CUDA_VERSION_ARG
+FROM nvidia/cuda:$CUDA_VERSION_ARG-devel-ubuntu16.04
+ARG CUDA_VERSION_ARG
 
 # Environment
 ENV DEBIAN_FRONTEND noninteractive
@@ -19,7 +19,7 @@ RUN \
 
 # NCCL2 (License: https://docs.nvidia.com/deeplearning/sdk/nccl-sla/index.html)
 RUN \
-    export CUDA_SHORT=`echo $CUDA_VERSION | egrep -o '[0-9]+\.[0-9]'` && \
+    export CUDA_SHORT=`echo $CUDA_VERSION_ARG | egrep -o '[0-9]+\.[0-9]'` && \
     export NCCL_VERSION=2.7.5-1 && \
     apt-get update && \
     apt-get install -y --allow-downgrades --allow-change-held-packages libnccl2=${NCCL_VERSION}+cuda${CUDA_SHORT} libnccl-dev=${NCCL_VERSION}+cuda${CUDA_SHORT}
diff --git a/tests/ci_build/Dockerfile.gpu_build_centos6 b/tests/ci_build/Dockerfile.gpu_build_centos6
index e755ce12a..b2adb8a06 100644
--- a/tests/ci_build/Dockerfile.gpu_build_centos6
+++ b/tests/ci_build/Dockerfile.gpu_build_centos6
@@ -1,6 +1,6 @@
-ARG CUDA_VERSION
-FROM nvidia/cuda:$CUDA_VERSION-devel-centos6
-ARG CUDA_VERSION
+ARG CUDA_VERSION_ARG
+FROM nvidia/cuda:$CUDA_VERSION_ARG-devel-centos6
+ARG CUDA_VERSION_ARG
 
 # Environment
 ENV DEBIAN_FRONTEND noninteractive
@@ -33,7 +33,7 @@ RUN \
 
 # NCCL2 (License: https://docs.nvidia.com/deeplearning/sdk/nccl-sla/index.html)
 RUN \
-    export CUDA_SHORT=`echo $CUDA_VERSION | egrep -o '[0-9]+\.[0-9]'` && \
+    export CUDA_SHORT=`echo $CUDA_VERSION_ARG | egrep -o '[0-9]+\.[0-9]'` && \
     export NCCL_VERSION=2.4.8-1 && \
     wget https://developer.download.nvidia.com/compute/machine-learning/repos/rhel7/x86_64/nvidia-machine-learning-repo-rhel7-1.0.0-1.x86_64.rpm && \
     rpm -i nvidia-machine-learning-repo-rhel7-1.0.0-1.x86_64.rpm && \
diff --git a/tests/ci_build/Dockerfile.gpu_jvm b/tests/ci_build/Dockerfile.gpu_jvm
index acd7b9b86..f11e739b1 100644
--- a/tests/ci_build/Dockerfile.gpu_jvm
+++ b/tests/ci_build/Dockerfile.gpu_jvm
@@ -1,5 +1,6 @@
-ARG CUDA_VERSION
-FROM nvidia/cuda:$CUDA_VERSION-runtime-ubuntu16.04
+ARG CUDA_VERSION_ARG
+FROM nvidia/cuda:$CUDA_VERSION_ARG-runtime-ubuntu16.04
+ARG CUDA_VERSION_ARG
 ARG JDK_VERSION=8
 ARG SPARK_VERSION=3.0.0
 
diff --git a/tests/ci_build/Dockerfile.jvm_gpu_build b/tests/ci_build/Dockerfile.jvm_gpu_build
index ed6c3d689..b0b46e6e9 100644
--- a/tests/ci_build/Dockerfile.jvm_gpu_build
+++ b/tests/ci_build/Dockerfile.jvm_gpu_build
@@ -1,6 +1,6 @@
-ARG CUDA_VERSION
-FROM nvidia/cuda:$CUDA_VERSION-devel-centos6
-ARG CUDA_VERSION
+ARG CUDA_VERSION_ARG
+FROM nvidia/cuda:$CUDA_VERSION_ARG-devel-centos6
+ARG CUDA_VERSION_ARG
 
 # Environment
 ENV DEBIAN_FRONTEND noninteractive
@@ -30,7 +30,7 @@ RUN \
 
 # NCCL2 (License: https://docs.nvidia.com/deeplearning/sdk/nccl-sla/index.html)
 RUN \
-    export CUDA_SHORT=`echo $CUDA_VERSION | egrep -o '[0-9]+\.[0-9]'` && \
+    export CUDA_SHORT=`echo $CUDA_VERSION_ARG | egrep -o '[0-9]+\.[0-9]'` && \
     export NCCL_VERSION=2.4.8-1 && \
     wget https://developer.download.nvidia.com/compute/machine-learning/repos/rhel7/x86_64/nvidia-machine-learning-repo-rhel7-1.0.0-1.x86_64.rpm && \
     rpm -i nvidia-machine-learning-repo-rhel7-1.0.0-1.x86_64.rpm && \