Fix race condition in GetCurrentNS temporarily (antrea-io#1131)

In GetCurrentNS, If there is a context-switch between
getCurrentThreadNetNSPath and GetNS, another goroutine may execute in
the original thread and change its network namespace, then the original
goroutine would get the updated network namespace, which could lead to
unexpected behavior, especially when GetCurrentNS is used to get the
host network namespace in netNS.Do.

Instead of using the provided netns argument, this patch fixes it by
getting the hostNS in advance with the OS thread locked.

pkg/agent/cniserver/interface_configuration_linux.go

@@ -19,6 +19,7 @@ package cniserver
 import (
 	"fmt"
 	"net"
+	"runtime"
 	"time"
 
 	"github.com/Mellanox/sriovnet"
@@ -194,7 +195,22 @@ func (ic *ifConfigurator) configureContainerLinkVeth(
 	hostIface := &current.Interface{Name: hostIfaceName}
 	containerIface := &current.Interface{Name: containerIfaceName, Sandbox: containerNetNS}
 	result.Interfaces = []*current.Interface{hostIface, containerIface}
-	if err := ns.WithNetNSPath(containerNetNS, func(hostNS ns.NetNS) error {
+
+	// This is a workaround for issue #1113, which is caused by https://github.com/containernetworking/plugins/issues/524.
+	// Instead of using the provided netns argument, which might not be the real hostNS, it fixes it by getting the
+	// hostNS in advance with the OS thread locked.
+	// TODO: remove this once the upstream issue is fixed.
+	hostNS, err := func() (ns.NetNS, error) {
+		runtime.LockOSThread()
+		defer runtime.UnlockOSThread()
+		return ns.GetCurrentNS()
+	}()
+	if err != nil {
+		return fmt.Errorf("failed to get host netns: %v", err)
+	}
+	defer hostNS.Close()
+
+	if err := ns.WithNetNSPath(containerNetNS, func(_ ns.NetNS) error {
 		klog.V(2).Infof("Creating veth devices (%s, %s) for container %s", containerIfaceName, hostIfaceName, containerID)
 		hostVeth, containerVeth, err := ip.SetupVethWithName(containerIfaceName, hostIfaceName, mtu, hostNS)
 		if err != nil {