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Fixes Issue # 23418: Race condition between device deferred removal and resume device.

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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 <shishir.mahajan@redhat.com>
This commit is contained in:
Shishir Mahajan 2016-06-09 13:52:25 -04:00
parent 2011320fa9
commit 0e633ee14a
2 changed files with 113 additions and 56 deletions
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62
pkg/devicemapper/devmapper.go
View file

@ -750,6 +750,33 @@ func activateDevice(poolName string, name string, deviceID int, size uint64, ext
return nil
}
// 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 {
return err
}
if err := task.setSector(0); err != nil {
return fmt.Errorf("devicemapper: Can't set sector %s", err)
}
if err := task.setMessage(fmt.Sprintf("create_snap %d %d", deviceID, baseDeviceID)); err != nil {
return fmt.Errorf("devicemapper: Can't set message %s", err)
}
dmSawExist = false // reset before the task is run
if err := task.run(); err != nil {
// 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)
@ -761,42 +788,15 @@ func CreateSnapDevice(poolName string, deviceID int, baseName string, baseDevice
}
}
task, err := TaskCreateNamed(deviceTargetMsg, poolName)
if task == nil {
if err := CreateSnapDeviceRaw(poolName, deviceID, baseDeviceID); err != nil {
if doSuspend {
ResumeDevice(baseName)
if err2 := ResumeDevice(baseName); err2 != nil {
return fmt.Errorf("CreateSnapDeviceRaw Error: (%v): ResumeDevice Error: (%v)", err, err2)
}
}
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)
}
if doSuspend {
if err := ResumeDevice(baseName); err != nil {
return err