@@ -105,14 +105,15 @@ type DiskUsage struct {

 }

 type Status struct {

-	PoolName         string

-	DataFile         string // actual block device for data

-	DataLoopback     string // loopback file, if used

-	MetadataFile     string // actual block device for metadata

-	MetadataLoopback string // loopback file, if used

-	Data             DiskUsage

-	Metadata         DiskUsage

-	SectorSize       uint64

+	PoolName          string

+	DataFile          string // actual block device for data

+	DataLoopback      string // loopback file, if used

+	MetadataFile      string // actual block device for metadata

+	MetadataLoopback  string // loopback file, if used

+	Data              DiskUsage

+	Metadata          DiskUsage

+	SectorSize        uint64

+	UdevSyncSupported bool

 }

 type DevStatus struct {

@@ -947,6 +948,12 @@ func (devices *DeviceSet) initDevmapper(doInit bool) error {

 		return graphdriver.ErrNotSupported

 	}

+	// https://github.com/docker/docker/issues/4036

+	if supported := devicemapper.UdevSetSyncSupport(true); !supported {

+		log.Warnf("WARNING: Udev sync is not supported. This will lead to unexpected behavior, data loss and errors")

+	}

+	log.Debugf("devicemapper: udev sync support: %v", devicemapper.UdevSyncSupported())

+

 	if err := os.MkdirAll(devices.metadataDir(), 0700); err != nil && !os.IsExist(err) {

 		return err

 	}

@@ -1572,6 +1579,7 @@ func (devices *DeviceSet) Status() *Status {

 	status.DataLoopback = devices.dataLoopFile

 	status.MetadataFile = devices.MetadataDevicePath()

 	status.MetadataLoopback = devices.metadataLoopFile

+	status.UdevSyncSupported = devicemapper.UdevSyncSupported()

 	totalSizeInSectors, _, dataUsed, dataTotal, metadataUsed, metadataTotal, err := devices.poolStatus()

 	if err == nil {

@@ -74,6 +74,7 @@ func (d *Driver) Status() [][2]string {

 		{"Data Space Total", fmt.Sprintf("%s", units.HumanSize(float64(s.Data.Total)))},

 		{"Metadata Space Used", fmt.Sprintf("%s", units.HumanSize(float64(s.Metadata.Used)))},

 		{"Metadata Space Total", fmt.Sprintf("%s", units.HumanSize(float64(s.Metadata.Total)))},

+		{"Udev Sync Supported", fmt.Sprintf("%v", s.UdevSyncSupported)},

 	}

 	if len(s.DataLoopback) > 0 {

 		status = append(status, [2]string{"Data loop file", s.DataLoopback})

@@ -319,6 +319,26 @@ func GetLibraryVersion() (string, error) {

 	return version, nil

 }

+// UdevSyncSupported returns whether device-mapper is able to sync with udev

+//

+// This is essential otherwise race conditions can arise where both udev and

+// device-mapper attempt to create and destroy devices.

+func UdevSyncSupported() bool {

+	return DmUdevGetSyncSupport() != 0

+}

+

+// UdevSetSyncSupport allows setting whether the udev sync should be enabled.

+// The return bool indicates the state of whether the sync is enabled.

+func UdevSetSyncSupport(enable bool) bool {

+	if enable {

+		DmUdevSetSyncSupport(1)

+	} else {

+		DmUdevSetSyncSupport(0)

+	}

+

+	return UdevSyncSupported()

+}

+

 // Useful helper for cleanup

 func RemoveDevice(name string) error {

 	log.Debugf("[devmapper] RemoveDevice START")

@@ -107,6 +107,8 @@ var (

 	DmTaskSetRo            = dmTaskSetRoFct

 	DmTaskSetSector        = dmTaskSetSectorFct

 	DmUdevWait             = dmUdevWaitFct

+	DmUdevSetSyncSupport   = dmUdevSetSyncSupportFct

+	DmUdevGetSyncSupport   = dmUdevGetSyncSupportFct

 	LogWithErrnoInit       = logWithErrnoInitFct

 )

@@ -231,6 +233,14 @@ func dmGetNextTargetFct(task *CDmTask, next uintptr, start, length *uint64, targ

 	return uintptr(nextp)

 }

+func dmUdevSetSyncSupportFct(syncWithUdev int) {

+	(C.dm_udev_set_sync_support(C.int(syncWithUdev)))

+}

+

+func dmUdevGetSyncSupportFct() int {

+	return int(C.dm_udev_get_sync_support())

+}

+

 func dmUdevWaitFct(cookie uint) int {

 	return int(C.dm_udev_wait(C.uint32_t(cookie)))

 }