If a host has multiple instance with the same shared
multi attach volume and you delete them in parallel
nova need to correctly clean up the volume connection on
the host when the last instance is removed.
currently we do not have a volume level lock to guard the
critical section that determins if the current disconnect is
removing the final usage of the volume.
This can lead to leaking the volume or other issues as
noted in bug: #2048837
This change introduces a FairLockGuard to ensure we acquire
and release the locks in a fair and orderd manner.
The FairLockGuard is used to lock the server delete with
one lock per multi attach volume.
This will ensure that disconnects of diffrent volumes can happen
in parallel but if we are disconnecting the same volume in multiple
greenthread concurrently they will be serialised.
Assisted-By: Cursor Auto
Closes-Bug: #2048837
Change-Id: I67e10cace451259127a5d7da8fbdf7739afe3e51
Signed-off-by: Sean Mooney <work@seanmooney.info>
Sean Mooney
22012360c4