Fix KVM incremental volume snapshot creation

agent/conf/agent.properties

@@ -457,3 +457,6 @@ iscsi.session.cleanup.enabled=false
 
 # Instance conversion VIRT_V2V_TMPDIR env var
 #convert.instance.env.virtv2v.tmpdir=
+
+# Time, in seconds, to wait before retrying to rebase during the incremental snapshot process.
+# incremental.snapshot.retry.rebase.wait=60

agent/src/main/java/com/cloud/agent/properties/AgentProperties.java

@@ -885,6 +885,11 @@ public Property<Integer> getWorkers() {
      */
     public static final Property<Boolean> CREATE_FULL_CLONE = new Property<>("create.full.clone", false);
 
+    /**
+     * Time, in seconds, to wait before retrying to rebase during the incremental snapshot process.
+     * */
+    public static final Property<Integer> INCREMENTAL_SNAPSHOT_RETRY_REBASE_WAIT = new Property<>("incremental.snapshot.retry.rebase.wait", 60);
+
 
     public static class Property <T>{
         private String name;

plugins/hypervisors/kvm/src/main/java/com/cloud/hypervisor/kvm/storage/KVMStorageProcessor.java

@@ -185,6 +185,8 @@ public class KVMStorageProcessor implements StorageProcessor {
 
     private int incrementalSnapshotTimeout;
 
+    private int incrementalSnapshotRetryRebaseWait;
+
     private static final String CHECKPOINT_XML_TEMP_DIR = "/tmp/cloudstack/checkpointXMLs";
 
     private static final String BACKUP_XML_TEMP_DIR = "/tmp/cloudstack/backupXMLs";
@@ -252,6 +254,7 @@ public boolean configure(final String name, final Map<String, Object> params) th
         _cmdsTimeout = AgentPropertiesFileHandler.getPropertyValue(AgentProperties.CMDS_TIMEOUT) * 1000;
 
         incrementalSnapshotTimeout = AgentPropertiesFileHandler.getPropertyValue(AgentProperties.INCREMENTAL_SNAPSHOT_TIMEOUT) * 1000;
+        incrementalSnapshotRetryRebaseWait = AgentPropertiesFileHandler.getPropertyValue(AgentProperties.INCREMENTAL_SNAPSHOT_RETRY_REBASE_WAIT) * 1000;
         return true;
     }
 
@@ -2093,8 +2096,25 @@ protected void rebaseSnapshot(SnapshotObjectTO snapshotObjectTO, KVMStoragePool
             QemuImg qemuImg = new QemuImg(wait);
             qemuImg.rebase(snapshotFile, parentSnapshotFile, PhysicalDiskFormat.QCOW2.toString(), false);
         } catch (LibvirtException | QemuImgException e) {
-            logger.error("Exception while rebasing incremental snapshot [{}] due to: [{}].", snapshotName, e.getMessage(), e);
-            throw new CloudRuntimeException(e);
+            if (!StringUtils.contains(e.getMessage(), "Is another process using the image")) {
+                logger.error("Exception while rebasing incremental snapshot [{}] due to: [{}].", snapshotName, e.getMessage(), e);
+                throw new CloudRuntimeException(e);
+            }
+            retryRebase(snapshotName, wait, e, snapshotFile, parentSnapshotFile);
+        }
+    }
+
+    private void retryRebase(String snapshotName, int wait, Exception e, QemuImgFile snapshotFile, QemuImgFile parentSnapshotFile) {
+        logger.warn("Libvirt still has not released the lock, will wait [{}] milliseconds and try again later.", incrementalSnapshotRetryRebaseWait);
+        try {
+            Thread.sleep(incrementalSnapshotRetryRebaseWait);
+            QemuImg qemuImg = new QemuImg(wait);
+            qemuImg.rebase(snapshotFile, parentSnapshotFile, PhysicalDiskFormat.QCOW2.toString(), false);
+        } catch (LibvirtException | QemuImgException | InterruptedException ex) {
+            logger.error("Unable to rebase snapshot [{}].", snapshotName, ex);
+            CloudRuntimeException cre = new CloudRuntimeException(ex);
+            cre.addSuppressed(e);
+            throw cre;
         }
     }