From a612434f4fa5da18833706885c24a1786dfac8e2 Mon Sep 17 00:00:00 2001 From: Shishir Mahajan Date: Wed, 31 Aug 2016 15:50:12 -0400 Subject: [PATCH] Sync with Upstream patch: Fixes Issue # 23418: Race condition between device deferred removal and resume device. Upstream PR: https://github.com/docker/docker/pull/23497 Problem Description: An example scenario that involves deferred removal 1. A new base image gets created (e.g. 'docker load -i'). The base device is activated and mounted at some point in time during image creation. 2. While image creation is in progress, a privileged container is started from another image and the host's mount name space is shared with this container ('docker run --privileged -v /:/host'). 3. Image creation completes and the base device gets unmounted. However, as the privileged container still holds a reference on the base image mount point, the base device cannot be removed right away. So it gets flagged for deferred removal. 4. Next, the privileged container terminates and thus its reference to the base image mount point gets released. The base device (which is flagged for deferred removal) may now be cleaned up by the device-mapper. This opens up an opportunity for a race between a 'kworker' thread (executing the do_deferred_remove() function) and the Docker daemon (executing the CreateSnapDevice() function). This PR cancel the deferred removal, if the device is marked for it. And reschedule the deferred removal later after the device is resumed successfully. Signed-off-by: Shishir Mahajan --- daemon/graphdriver/devmapper/deviceset.go | 105 +++++++++++++++++----- pkg/devicemapper/devmapper.go | 48 +++++----- 2 files changed, 105 insertions(+), 48 deletions(-) diff --git a/daemon/graphdriver/devmapper/deviceset.go b/daemon/graphdriver/devmapper/deviceset.go index 3586c3ee92e5d..7052e6ac738f8 100644 --- a/daemon/graphdriver/devmapper/deviceset.go +++ b/daemon/graphdriver/devmapper/deviceset.go @@ -529,7 +529,7 @@ func (devices *DeviceSet) activateDeviceIfNeeded(info *devInfo, ignoreDeleted bo // Make sure deferred removal on device is canceled, if one was // scheduled. - if err := devices.cancelDeferredRemoval(info); err != nil { + if err := devices.cancelDeferredRemovalIfNeeded(info); err != nil { return fmt.Errorf("devmapper: Device Deferred Removal Cancellation Failed: %s", err) } @@ -842,11 +842,56 @@ func (devices *DeviceSet) createRegisterDevice(hash string) (*devInfo, error) { return info, nil } -func (devices *DeviceSet) createRegisterSnapDevice(hash string, baseInfo *devInfo) error { - if err := devices.poolHasFreeSpace(); err != nil { +func (devices *DeviceSet) takeSnapshot(hash string, baseInfo *devInfo) error { + var ( + devinfo *devicemapper.Info + err error + ) + + if err = devices.poolHasFreeSpace(); err != nil { + return err + } + + if devices.deferredRemove { + devinfo, err = devicemapper.GetInfoWithDeferred(baseInfo.Name()) + if err != nil { + return err + } + if devinfo != nil && devinfo.DeferredRemove != 0 { + err = devices.cancelDeferredRemoval(baseInfo) + if err != nil { + // If Error is ErrEnxio. Device is probably already gone. Continue. + if err != devicemapper.ErrEnxio { + return err + } + } else { + defer devices.deactivateDevice(baseInfo) + } + } + } else { + devinfo, err = devicemapper.GetInfo(baseInfo.Name()) + if err != nil { + return err + } + } + + doSuspend := devinfo != nil && devinfo.Exists != 0 + + if doSuspend { + if err = devicemapper.SuspendDevice(baseInfo.Name()); err != nil { + return err + } + defer devicemapper.ResumeDevice(baseInfo.Name()) + } + + if err = devices.createRegisterSnapDevice(hash, baseInfo); err != nil { return err } + return nil +} + +func (devices *DeviceSet) createRegisterSnapDevice(hash string, baseInfo *devInfo) error { deviceID, err := devices.getNextFreeDeviceID() if err != nil { return err @@ -859,7 +904,7 @@ func (devices *DeviceSet) createRegisterSnapDevice(hash string, baseInfo *devInf } for { - if err := devicemapper.CreateSnapDevice(devices.getPoolDevName(), deviceID, baseInfo.Name(), baseInfo.DeviceID); err != nil { + if err := devicemapper.CreateSnapDeviceRaw(devices.getPoolDevName(), deviceID, baseInfo.DeviceID); err != nil { if devicemapper.DeviceIDExists(err) { // Device ID already exists. This should not // happen. Now we have a mechanism to find @@ -1856,7 +1901,7 @@ func (devices *DeviceSet) AddDevice(hash, baseHash string) error { return fmt.Errorf("devmapper: device %s already exists. Deleted=%v", hash, info.Deleted) } - if err := devices.createRegisterSnapDevice(hash, baseInfo); err != nil { + if err := devices.takeSnapshot(hash, baseInfo); err != nil { return err } @@ -2073,41 +2118,53 @@ func (devices *DeviceSet) removeDevice(devname string) error { return err } -func (devices *DeviceSet) cancelDeferredRemoval(info *devInfo) error { +func (devices *DeviceSet) cancelDeferredRemovalIfNeeded(info *devInfo) error { if !devices.deferredRemove { return nil } - logrus.Debugf("devmapper: cancelDeferredRemoval START(%s)", info.Name()) - defer logrus.Debugf("devmapper: cancelDeferredRemoval END(%s)", info.Name()) + logrus.Debugf("devmapper: cancelDeferredRemovalIfNeeded START(%s)", info.Name()) + defer logrus.Debugf("devmapper: cancelDeferredRemovalIfNeeded END(%s)", info.Name()) devinfo, err := devicemapper.GetInfoWithDeferred(info.Name()) + if err != nil { + return err + } if devinfo != nil && devinfo.DeferredRemove == 0 { return nil } // Cancel deferred remove - for i := 0; i < 100; i++ { - err = devicemapper.CancelDeferredRemove(info.Name()) - if err == nil { - break + if err := devices.cancelDeferredRemoval(info); err != nil { + // If Error is ErrEnxio. Device is probably already gone. Continue. + if err != devicemapper.ErrEnxio { + return err } + } + return nil +} - if err == devicemapper.ErrEnxio { - // Device is probably already gone. Return success. - return nil - } +func (devices *DeviceSet) cancelDeferredRemoval(info *devInfo) error { + logrus.Debugf("devmapper: cancelDeferredRemoval START(%s)", info.Name()) + defer logrus.Debugf("devmapper: cancelDeferredRemoval END(%s)", info.Name()) - if err != devicemapper.ErrBusy { - return err - } + var err error - // If we see EBUSY it may be a transient error, - // sleep a bit a retry a few times. - devices.Unlock() - time.Sleep(100 * time.Millisecond) - devices.Lock() + // Cancel deferred remove + for i := 0; i < 100; i++ { + err = devicemapper.CancelDeferredRemove(info.Name()) + if err != nil { + if err == devicemapper.ErrBusy { + // If we see EBUSY it may be a transient error, + // sleep a bit a retry a few times. + devices.Unlock() + time.Sleep(100 * time.Millisecond) + devices.Lock() + continue + } + } + break } return err } diff --git a/pkg/devicemapper/devmapper.go b/pkg/devicemapper/devmapper.go index 7da60ca7920e7..fa862f9de619c 100644 --- a/pkg/devicemapper/devmapper.go +++ b/pkg/devicemapper/devmapper.go @@ -771,51 +771,51 @@ func activateDevice(poolName string, name string, deviceID int, size uint64, ext return nil } -// CreateSnapDevice creates a snapshot based on the device identified by the baseName and baseDeviceId, -func CreateSnapDevice(poolName string, deviceID int, baseName string, baseDeviceID int) error { - devinfo, _ := GetInfo(baseName) - doSuspend := devinfo != nil && devinfo.Exists != 0 - - if doSuspend { - if err := SuspendDevice(baseName); err != nil { - return err - } - } - +// CreateSnapDeviceRaw creates a snapshot device. Caller needs to suspend and resume the origin device if it is active. +func CreateSnapDeviceRaw(poolName string, deviceID int, baseDeviceID int) error { task, err := TaskCreateNamed(deviceTargetMsg, poolName) if task == nil { - if doSuspend { - ResumeDevice(baseName) - } return err } if err := task.setSector(0); err != nil { - if doSuspend { - ResumeDevice(baseName) - } return fmt.Errorf("devicemapper: Can't set sector %s", err) } if err := task.setMessage(fmt.Sprintf("create_snap %d %d", deviceID, baseDeviceID)); err != nil { - if doSuspend { - ResumeDevice(baseName) - } return fmt.Errorf("devicemapper: Can't set message %s", err) } dmSawExist = false // reset before the task is run if err := task.run(); err != nil { - if doSuspend { - ResumeDevice(baseName) - } // Caller wants to know about ErrDeviceIDExists so that it can try with a different device id. if dmSawExist { return ErrDeviceIDExists } - return fmt.Errorf("devicemapper: Error running deviceCreate (createSnapDevice) %s", err) + } + + return nil +} + +// CreateSnapDevice creates a snapshot based on the device identified by the baseName and baseDeviceId, +func CreateSnapDevice(poolName string, deviceID int, baseName string, baseDeviceID int) error { + devinfo, _ := GetInfo(baseName) + doSuspend := devinfo != nil && devinfo.Exists != 0 + if doSuspend { + if err := SuspendDevice(baseName); err != nil { + return err + } + } + + if err := CreateSnapDeviceRaw(poolName, deviceID, baseDeviceID); err != nil { + if doSuspend { + if err2 := ResumeDevice(baseName); err2 != nil { + return fmt.Errorf("CreateSnapDeviceRaw Error: (%v): ResumeDevice Error: (%v)", err, err2) + } + } + return err } if doSuspend {