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Sample of Defect

Project Name CID Checker Category Developer Description
ovirt-engine 1323817 NULL_RETURNS Null pointer dereferences Possible Null Pointer exception was found in a feature in which I'm the feature owner. That exception could have rendered the entire feature non operational (And many log messages that the user wouldn't understand).
File: /backend/manager/modules/bll/src/main/java/org/ovirt/engine/core/bll/scheduling/arem/AffinityRulesEnforcer.java 
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    private static final Logger log = LoggerFactory.getLogger(AffinityRulesEnforcer.class);

    @Inject
    private AffinityGroupDao affinityGroupDao;
    @Inject
    private VmDao vmDao;
    @Inject
    private SchedulingManager schedulingManager;
    private final Random random = new Random();

    protected enum FailMode {
        IMMEDIATELY, // Fail when first violation is detected
        GET_ALL // Collect all violations
    }

    public VM chooseNextVmToMigrate(VDSGroup vdsGroup) {
        List<AffinityGroup> allHardAffinityGroups = getAllHardAffinityGroups(vdsGroup);

        Set<Set<Guid>> unifiedPositiveAffinityGroups = AffinityRulesUtils.getUnifiedPositiveAffinityGroups(
                allHardAffinityGroups);
        List<AffinityGroup> unifiedAffinityGroups = AffinityRulesUtils.setsToAffinityGroups(
                unifiedPositiveAffinityGroups);

        // Add negative affinity groups
 
 < 1. Iterating over another element of "allHardAffinityGroups"
 < 4. No elements left in "allHardAffinityGroups", leaving loop
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        for (AffinityGroup ag : allHardAffinityGroups) {
 
 < 2. Condition "!ag.isPositive()", taking true branch
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            if (!ag.isPositive()) {
                unifiedAffinityGroups.add(ag);
            }
 
 < 3. Jumping back to the beginning of the loop
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        }

        // Create a set of all VMs in affinity groups
        Set<Guid> allVms = new HashSet<>();
 
 < 5. Iterating over another element of "unifiedAffinityGroups"
 < 7. No elements left in "unifiedAffinityGroups", leaving loop
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        for (AffinityGroup group : unifiedAffinityGroups) {
            allVms.addAll(group.getEntityIds());
 
 < 6. Jumping back to the beginning of the loop
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        }

        Map<Guid, Guid> vmToHost = createMapOfVmToHost(allVms);

        // There is no need to migrate when no collision was detected
        Set<AffinityGroup> violatedAffinityGroups =
                checkForAffinityGroupViolations(unifiedAffinityGroups, vmToHost, FailMode.GET_ALL);
 
 < 8. Condition "violatedAffinityGroups.isEmpty()", taking false branch
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        if (violatedAffinityGroups.isEmpty()) {
            log.debug("No affinity group collision detected for cluster {}. Standing by.", vdsGroup.getId());
            return null;
        }

        // Find a VM that is breaking the affinityGroup and can be theoretically migrated
        // - start with bigger Affinity Groups
        List<AffinityGroup> affGroupsBySize = new ArrayList<>(violatedAffinityGroups);
        Collections.sort(affGroupsBySize, Collections.reverseOrder(new AffinityGroupComparator()));

 < 9. Iterating over another element of "affGroupsBySize"
 < 14. Iterating over another element of "affGroupsBySize"
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        for (AffinityGroup affinityGroup : affGroupsBySize) {
            final List<VM> candidateVms;

 < 10. Condition "affinityGroup.isPositive()", taking true branch
 < 15. Condition "affinityGroup.isPositive()", taking true branch
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            if (affinityGroup.isPositive()) {
 
 <<< CID 1323817: Null pointer dereferences NULL_RETURNS
 <<< 16. "findVmViolatingPositiveAg" returns null (checked 0 out of 1 times).
 <<< CID 1323817: Null pointer dereferences NULL_RETURNS
 <<< 17. Dereferencing a pointer that might be null "findVmViolatingPositiveAg(affinityGroup, vmToHost)" when calling "getVmsByIds". (The virtual call resolves to "org.ovirt.engine.core.dao.VmDaoImpl.getVmsByIds".)
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                candidateVms = vmDao.getVmsByIds(findVmViolatingPositiveAg(affinityGroup, vmToHost));
                log.info("Positive affinity group violation detected");
 
 < 11. Falling through to end of if statement
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            } else {
                candidateVms = vmDao.getVmsByIds(findVmViolatingNegativeAg(affinityGroup, vmToHost));
                log.info("Negative affinity group violation detected");
            }

 < 12. Condition "!candidateVms.isEmpty()", taking false branch
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            while (!candidateVms.isEmpty()) {
                final int index = random.nextInt(candidateVms.size());
                final VM candidateVm = candidateVms.get(index);

                // Test whether any migration is possible, this uses current AffinityGroup settings
                // and so won't allow more breakage
                boolean canMove = schedulingManager.canSchedule(vdsGroup, candidateVm,
                        new ArrayList<Guid>(), new ArrayList<Guid>(),
                        null, new ArrayList<String>());

                if (canMove) {
                    log.debug("VM {} is a viable candidate for solving affinity group violation situation.",
                            candidateVm.getId());
                    return candidateVm;
                }
                log.debug("VM {} is NOT a viable candidate for solving affinity group violation situation.",
                        candidateVm.getId());
                candidateVms.remove(index);
            }

 < 13. Jumping back to the beginning of the loop
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        }

        // No possible migration..
        return null;
    }

    private Map<Guid, Guid> createMapOfVmToHost(Set<Guid> allVms) {
        Map<Guid, Guid> outputMap = new HashMap<>();

        for (VM vm : vmDao.getVmsByIds(new ArrayList<>(allVms))) {
            Guid hostId = vm.getRunOnVds();

            if (hostId != null) {
                outputMap.put(vm.getId(), hostId);
            }
        }

        return outputMap;
    }

    /**
     * Select VMs from the broken affinity group that are running on the same host.
     *
     * @param affinityGroup broken affinity rule
     * @param vmToHost      vm to host assignments
     * @return a list of vms which are candidates for migration
     */
Events:
16. returned_null AffinityRulesEnforcer.java:92
17. dereference AffinityRulesEnforcer.java:92

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