In Druid, Killing segments means removing the segment files from the deep storage and deletes the entries from the metadata store. This is currently done using KillTask. Since it's a task, it first gets taskLocks and do the below:

    final List<DataSegment> unusedSegments = toolbox
        .getTaskActionClient()
        .submit(new SegmentListUnusedAction(getDataSource(), getInterval()));

    if (!TaskActionPreconditions.isLockCoversSegments(taskLockMap, unusedSegments)) {
      throw new ISE(
          "Locks[%s] for task[%s] can't cover segments[%s]",
          taskLockMap.values().stream().flatMap(List::stream).collect(Collectors.toList()),
          getId(),
          unusedSegments
      );
    }

    // Kill segments
    for (DataSegment segment : unusedSegments) {
      toolbox.getDataSegmentKiller().kill(segment);
      toolbox.getTaskActionClient().submit(new SegmentNukeAction(ImmutableSet.of(segment)));
    }

However, the coordinator provides an HTTP endpoint to enable a segment (setting used = true for a segment) which can happen between SegmentListUnusedAction and SegmentNukeAction without getting a taskLock.

Also, the order of killing segments should be changed: the metadata store must be updated first before removing the segment file.

I think we may change the way of killing segments to not use the task. Instead, the coordinator can kill segments directly because enabling/disabling existing segments happens only in the coordinator.