[4.6] libct/cg/sd: reconnect and retry on dbus connection error

libcontainer/cgroups/systemd/common.go

@@ -20,13 +20,8 @@ import (
 )
 
 var (
-	connOnce sync.Once
-	connDbus *systemdDbus.Conn
-	connErr  error
-
 	versionOnce sync.Once
 	version     int
-	versionErr  error
 
 	isRunningSystemdOnce sync.Once
 	isRunningSystemd     bool
@@ -284,19 +279,6 @@ func generateDeviceProperties(rules []*configs.DeviceRule) ([]systemdDbus.Proper
 	return properties, nil
 }
 
-// getDbusConnection lazy initializes systemd dbus connection
-// and returns it
-func getDbusConnection(rootless bool) (*systemdDbus.Conn, error) {
-	connOnce.Do(func() {
-		if rootless {
-			connDbus, connErr = NewUserSystemdDbus()
-		} else {
-			connDbus, connErr = systemdDbus.New()
-		}
-	})
-	return connDbus, connErr
-}
-
 func newProp(name string, units interface{}) systemdDbus.Property {
 	return systemdDbus.Property{
 		Name:  name,
@@ -312,19 +294,29 @@ func getUnitName(c *configs.Cgroup) string {
 	return c.Name
 }
 
-// isUnitExists returns true if the error is that a systemd unit already exists.
-func isUnitExists(err error) bool {
+// isDbusError returns true if the error is a specific dbus error.
+func isDbusError(err error, name string) bool {
 	if err != nil {
-		if dbusError, ok := err.(dbus.Error); ok {
-			return strings.Contains(dbusError.Name, "org.freedesktop.systemd1.UnitExists")
+		var derr *dbus.Error
+		if errors.As(err, &derr) {
+			return strings.Contains(derr.Name, name)
 		}
 	}
 	return false
 }
 
-func startUnit(dbusConnection *systemdDbus.Conn, unitName string, properties []systemdDbus.Property) error {
+// isUnitExists returns true if the error is that a systemd unit already exists.
+func isUnitExists(err error) bool {
+	return isDbusError(err, "org.freedesktop.systemd1.UnitExists")
+}
+
+func startUnit(cm *dbusConnManager, unitName string, properties []systemdDbus.Property) error {
 	statusChan := make(chan string, 1)
-	if _, err := dbusConnection.StartTransientUnit(unitName, "replace", properties, statusChan); err == nil {
+	err := cm.retryOnDisconnect(func(c *systemdDbus.Conn) error {
+		_, err := c.StartTransientUnit(unitName, "replace", properties, statusChan)
+		return err
+	})
+	if err == nil {
 		timeout := time.NewTimer(30 * time.Second)
 		defer timeout.Stop()
 
@@ -333,11 +325,11 @@ func startUnit(dbusConnection *systemdDbus.Conn, unitName string, properties []s
 			close(statusChan)
 			// Please refer to https://godoc.org/github.com/coreos/go-systemd/dbus#Conn.StartUnit
 			if s != "done" {
-				dbusConnection.ResetFailedUnit(unitName)
+				resetFailedUnit(cm, unitName)
 				return errors.Errorf("error creating systemd unit `%s`: got `%s`", unitName, s)
 			}
 		case <-timeout.C:
-			dbusConnection.ResetFailedUnit(unitName)
+			resetFailedUnit(cm, unitName)
 			return errors.New("Timeout waiting for systemd to create " + unitName)
 		}
 	} else if !isUnitExists(err) {
@@ -347,9 +339,13 @@ func startUnit(dbusConnection *systemdDbus.Conn, unitName string, properties []s
 	return nil
 }
 
-func stopUnit(dbusConnection *systemdDbus.Conn, unitName string) error {
+func stopUnit(cm *dbusConnManager, unitName string) error {
 	statusChan := make(chan string, 1)
-	if _, err := dbusConnection.StopUnit(unitName, "replace", statusChan); err == nil {
+	err := cm.retryOnDisconnect(func(c *systemdDbus.Conn) error {
+		_, err := c.StopUnit(unitName, "replace", statusChan)
+		return err
+	})
+	if err == nil {
 		select {
 		case s := <-statusChan:
 			close(statusChan)
@@ -364,20 +360,40 @@ func stopUnit(dbusConnection *systemdDbus.Conn, unitName string) error {
 	return nil
 }
 
-func systemdVersion(conn *systemdDbus.Conn) (int, error) {
+func resetFailedUnit(cm *dbusConnManager, name string) {
+	err := cm.retryOnDisconnect(func(c *systemdDbus.Conn) error {
+		return c.ResetFailedUnit(name)
+	})
+	if err != nil {
+		logrus.Warnf("unable to reset failed unit: %v", err)
+	}
+}
+
+func setUnitProperties(cm *dbusConnManager, name string, properties ...systemdDbus.Property) error {
+	return cm.retryOnDisconnect(func(c *systemdDbus.Conn) error {
+		return c.SetUnitProperties(name, true, properties...)
+	})
+}
+
+func systemdVersion(cm *dbusConnManager) int {
 	versionOnce.Do(func() {
 		version = -1
-		verStr, err := conn.GetManagerProperty("Version")
-		if err != nil {
-			versionErr = err
-			return
+		var verStr string
+		err := cm.retryOnDisconnect(func(c *systemdDbus.Conn) error {
+			var err error
+			verStr, err = c.GetManagerProperty("Version")
+			return err
+		})
+		if err == nil {
+			version, err = systemdVersionAtoi(verStr)
 		}
 
-		version, versionErr = systemdVersionAtoi(verStr)
-		return
+		if err != nil {
+			logrus.WithError(err).Error("unable to get systemd version")
+		}
 	})
 
-	return version, versionErr
+	return version
 }
 
 func systemdVersionAtoi(verStr string) (int, error) {
@@ -395,13 +411,11 @@ func systemdVersionAtoi(verStr string) (int, error) {
 	return ver, errors.Wrapf(err, "can't parse version %s", verStr)
 }
 
-func addCpuQuota(conn *systemdDbus.Conn, properties *[]systemdDbus.Property, quota int64, period uint64) {
+func addCpuQuota(cm *dbusConnManager, properties *[]systemdDbus.Property, quota int64, period uint64) {
 	if period != 0 {
 		// systemd only supports CPUQuotaPeriodUSec since v242
-		sdVer, err := systemdVersion(conn)
-		if err != nil {
-			logrus.Warnf("systemdVersion: %s", err)
-		} else if sdVer >= 242 {
+		sdVer := systemdVersion(cm)
+		if sdVer >= 242 {
 			*properties = append(*properties,
 				newProp("CPUQuotaPeriodUSec", period))
 		}

libcontainer/cgroups/systemd/dbus.go

@@ -0,0 +1,89 @@
+// +build linux
+
+package systemd
+
+import (
+	"sync"
+
+	systemdDbus "github.com/coreos/go-systemd/v22/dbus"
+	dbus "github.com/godbus/dbus/v5"
+)
+
+type dbusConnManager struct {
+	conn     *systemdDbus.Conn
+	rootless bool
+	sync.RWMutex
+}
+
+// newDbusConnManager initializes systemd dbus connection manager.
+func newDbusConnManager(rootless bool) *dbusConnManager {
+	return &dbusConnManager{
+		rootless: rootless,
+	}
+}
+
+// getConnection lazily initializes and returns systemd dbus connection.
+func (d *dbusConnManager) getConnection() (*systemdDbus.Conn, error) {
+	// In the case where d.conn != nil
+	// Use the read lock the first time to ensure
+	// that Conn can be acquired at the same time.
+	d.RLock()
+	if conn := d.conn; conn != nil {
+		d.RUnlock()
+		return conn, nil
+	}
+	d.RUnlock()
+
+	// In the case where d.conn == nil
+	// Use write lock to ensure that only one
+	// will be created
+	d.Lock()
+	defer d.Unlock()
+	if conn := d.conn; conn != nil {
+		return conn, nil
+	}
+
+	conn, err := d.newConnection()
+	if err != nil {
+		return nil, err
+	}
+	d.conn = conn
+	return conn, nil
+}
+
+func (d *dbusConnManager) newConnection() (*systemdDbus.Conn, error) {
+	if d.rootless {
+		return newUserSystemdDbus()
+	}
+	return systemdDbus.New()
+}
+
+// resetConnection resets the connection to its initial state
+// (so it can be reconnected if necessary).
+func (d *dbusConnManager) resetConnection(conn *systemdDbus.Conn) {
+	d.Lock()
+	defer d.Unlock()
+	if d.conn != nil && d.conn == conn {
+		d.conn.Close()
+		d.conn = nil
+	}
+}
+
+var errDbusConnClosed = dbus.ErrClosed.Error()
+
+// retryOnDisconnect calls op, and if the error it returns is about closed dbus
+// connection, the connection is re-established and the op is retried. This helps
+// with the situation when dbus is restarted and we have a stale connection.
+func (d *dbusConnManager) retryOnDisconnect(op func(*systemdDbus.Conn) error) error {
+	for {
+		conn, err := d.getConnection()
+		if err != nil {
+			return err
+		}
+		err = op(conn)
+		if !isDbusError(err, errDbusConnClosed) {
+			return err
+		}
+		d.resetConnection(conn)
+	}
+}

libcontainer/cgroups/systemd/user.go

@@ -17,8 +17,8 @@ import (
 	"github.com/pkg/errors"
 )
 
-// NewUserSystemdDbus creates a connection for systemd user-instance.
-func NewUserSystemdDbus() (*systemdDbus.Conn, error) {
+// newUserSystemdDbus creates a connection for systemd user-instance.
+func newUserSystemdDbus() (*systemdDbus.Conn, error) {
 	addr, err := DetectUserDbusSessionBusAddress()
 	if err != nil {
 		return nil, err

libcontainer/cgroups/systemd/v1.go

@@ -21,12 +21,14 @@ type legacyManager struct {
 	mu      sync.Mutex
 	cgroups *configs.Cgroup
 	paths   map[string]string
+	dbus    *dbusConnManager
 }
 
 func NewLegacyManager(cg *configs.Cgroup, paths map[string]string) cgroups.Manager {
 	return &legacyManager{
 		cgroups: cg,
 		paths:   paths,
+		dbus:    newDbusConnManager(false),
 	}
 }
 
@@ -57,7 +59,7 @@ var legacySubsystems = []subsystem{
 	&fs.NameGroup{GroupName: "name=systemd"},
 }
 
-func genV1ResourcesProperties(c *configs.Cgroup, conn *systemdDbus.Conn) ([]systemdDbus.Property, error) {
+func genV1ResourcesProperties(c *configs.Cgroup, cm *dbusConnManager) ([]systemdDbus.Property, error) {
 	var properties []systemdDbus.Property
 	r := c.Resources
 
@@ -77,7 +79,7 @@ func genV1ResourcesProperties(c *configs.Cgroup, conn *systemdDbus.Conn) ([]syst
 			newProp("CPUShares", r.CpuShares))
 	}
 
-	addCpuQuota(conn, &properties, r.CpuQuota, r.CpuPeriod)
+	addCpuQuota(cm, &properties, r.CpuQuota, r.CpuPeriod)
 
 	if r.BlkioWeight != 0 {
 		properties = append(properties,
@@ -155,11 +157,7 @@ func (m *legacyManager) Apply(pid int) error {
 	properties = append(properties,
 		newProp("DefaultDependencies", false))
 
-	dbusConnection, err := getDbusConnection(false)
-	if err != nil {
-		return err
-	}
-	resourcesProperties, err := genV1ResourcesProperties(c, dbusConnection)
+	resourcesProperties, err := genV1ResourcesProperties(c, m.dbus)
 	if err != nil {
 		return err
 	}
@@ -174,7 +172,7 @@ func (m *legacyManager) Apply(pid int) error {
 		}
 	}
 
-	if err := startUnit(dbusConnection, unitName, properties); err != nil {
+	if err := startUnit(m.dbus, unitName, properties); err != nil {
 		return err
 	}
 
@@ -212,13 +210,8 @@ func (m *legacyManager) Destroy() error {
 	m.mu.Lock()
 	defer m.mu.Unlock()
 
-	dbusConnection, err := getDbusConnection(false)
-	if err != nil {
-		return err
-	}
-	unitName := getUnitName(m.cgroups)
+	stopErr := stopUnit(m.dbus, getUnitName(m.cgroups))
 
-	stopErr := stopUnit(dbusConnection, unitName)
 	// Both on success and on error, cleanup all the cgroups we are aware of.
 	// Some of them were created directly by Apply() and are not managed by systemd.
 	if err := cgroups.RemovePaths(m.paths); err != nil {
@@ -342,11 +335,7 @@ func (m *legacyManager) Set(container *configs.Config) error {
 	if m.cgroups.Paths != nil {
 		return nil
 	}
-	dbusConnection, err := getDbusConnection(false)
-	if err != nil {
-		return err
-	}
-	properties, err := genV1ResourcesProperties(container.Cgroups, dbusConnection)
+	properties, err := genV1ResourcesProperties(container.Cgroups, m.dbus)
 	if err != nil {
 		return err
 	}
@@ -374,7 +363,7 @@ func (m *legacyManager) Set(container *configs.Config) error {
 		}
 	}
 
-	if err := dbusConnection.SetUnitProperties(getUnitName(container.Cgroups), true, properties...); err != nil {
+	if err := setUnitProperties(m.dbus, getUnitName(container.Cgroups), properties...); err != nil {
 		_ = m.Freeze(targetFreezerState)
 		return err
 	}