For the usage corrupted issue, it can be reproduced by file, iscsi backend with luks usage.
Not reproduced by gluster with luks uuid.

Does the crash happen if you start a clean libvirtd and retry the steps just once? I've identified a double-free regarding the 'usage' string, but that manifests itself only after you destroy the VM and start it again.

(In reply to Peter Krempa from comment #2)
> Does the crash happen if you start a clean libvirtd and retry the steps just
> once? I've identified a double-free regarding the 'usage' string, but that
> manifests itself only after you destroy the VM and start it again.

The crash will not happen when following 1~5 with a fresh libvirtd:
➜  luks virsh start new           
Domain new started

➜  luks virsh blockcopy new sda --xml file-dest.xml --pivot --transient-job --verbose --wait --reuse-external
Block Copy: [100 %]
Successfully pivoted
➜  luks virsh destroy new                                                                                    
Domain new destroyed

➜  luks virsh dumpxml new |xmllint --xpath //disk -
-:48: parser error : Input is not proper UTF-8, indicate encoding !
Bytes: 0xC0 0x94 0xBB 0x7F
        <secret type='passphrase' usage=''/>

I have installed rpm of v6.1.0-190-gaeb909bf9b, which includes:
commit 38bc76bcc1e1bccb7f3265e15b60b0f6f8fe6dfa
Author: Peter Krempa <pkrempa>
Date:   Fri Mar 6 14:44:43 2020 +0100

    qemu: Don't take double pointer in qemuDomainSecretInfoFree
    
    Using a double pointer prevents the function from being used as the
    automatic cleanup function for the given type.
    
    Remove the double pointer use by replacing the calls with
    g_clear_pointer which ensures that the pointer is cleared.
    
    Signed-off-by: Peter Krempa <pkrempa>
    Reviewed-by: Ján Tomko <jtomko>


But the error in comment3 could be reproduced again.

(In reply to Han Han from comment #3)
> (In reply to Peter Krempa from comment #2)
> > Does the crash happen if you start a clean libvirtd and retry the steps just
> > once? I've identified a double-free regarding the 'usage' string, but that
> > manifests itself only after you destroy the VM and start it again.
> 
> The crash will not happen when following 1~5 with a fresh libvirtd:
> ➜  luks virsh start new           
> Domain new started
> 
> ➜  luks virsh blockcopy new sda --xml file-dest.xml --pivot --transient-job
> --verbose --wait --reuse-external
> Block Copy: [100 %]
> Successfully pivoted
> ➜  luks virsh destroy new                                           


Thank you for confirming.
        
> 
> Domain new destroyed
> 
> ➜  luks virsh dumpxml new |xmllint --xpath //disk -
> -:48: parser error : Input is not proper UTF-8, indicate encoding !
> Bytes: 0xC0 0x94 0xBB 0x7F
>         <secret type='passphrase' usage=''/>

I've seen this symptom while debugging.

(In reply to Han Han from comment #4)
> I have installed rpm of v6.1.0-190-gaeb909bf9b, which includes:
> commit 38bc76bcc1e1bccb7f3265e15b60b0f6f8fe6dfa
> Author: Peter Krempa <pkrempa>
> Date:   Fri Mar 6 14:44:43 2020 +0100
> 
>     qemu: Don't take double pointer in qemuDomainSecretInfoFree
>     
>     Using a double pointer prevents the function from being used as the
>     automatic cleanup function for the given type.
>     
>     Remove the double pointer use by replacing the calls with
>     g_clear_pointer which ensures that the pointer is cleared.
>     
>     Signed-off-by: Peter Krempa <pkrempa>
>     Reviewed-by: Ján Tomko <jtomko>
> 
> 
> But the error in comment3 could be reproduced again.

That one was just a simplification of the code. The proper fix for the issue should be the patch I've posted for a wrong copy of the 'usage' string:

https://www.redhat.com/archives/libvir-list/2020-March/msg00693.html

Fixed upstream:

commit 299796328c34a30295d6cdc7ebce5d65843e921f
Author: Peter Krempa <pkrempa>
Date:   Thu Mar 19 15:38:06 2020 +0100

    virStorageEncryptionSecretCopy: Properly copy internals
    
    virStorageEncryptionSecretPtr may have a string inside it, thus we must
    copy the string too. Use virSecretLookupDefCopy to do that.
    
    Caused by non-obvious code introduced in 756b46ddd24 and later 47e88b33b
    which added a string that needed to be copied.
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1814923
    
    Signed-off-by: Peter Krempa <pkrempa>
    Reviewed-by: Ján Tomko <jtomko>
    Reviewed-by: Michal Privoznik <mprivozn>

commit 02f909b8a6ad8c271693fed9ceab606f0dda2294
Author: Peter Krempa <pkrempa>
Date:   Thu Mar 19 15:27:40 2020 +0100

    virSecretLookupDefCopy: Remove return value
    
    The function always returns succes so there's no need for a return
    value.
    
    Signed-off-by: Peter Krempa <pkrempa>
    Reviewed-by: Ján Tomko <jtomko>
    Reviewed-by: Michal Privoznik <mprivozn>

Vefified on libvirt-6.0.0-17.module+el8.2.0+6257+0d066c28.x86_64
qemu-kvm-4.2.0-17.module+el8.2.0+6141+0f540f16.x86_64:

1. Start a VM

2. Prepare luks secret and set the password

3. Blockcopy to a luks disk:
# cat /tmp/file-dest.xml 
<disk type="file" device="disk">
  <driver name="qemu" type="qcow2"/>
  <source file="/var/lib/libvirt/images/pc-luks">
    <encryption format="luks">
      <secret type="passphrase" usage="luks"/>
    </encryption>
  </source>
  <target dev="sda" bus="scsi"/>
</disk>

➜  ~ virsh blockcopy pc sda --xml /tmp/file-dest.xml --wait --verbose --transient-job
Block Copy: [100 %]

➜  ~ virsh blockjob pc sda --pivot  

➜  ~ virsh dumpxml pc | xmllint --xpath //disk -
<disk type="file" device="disk">
      <driver name="qemu" type="qcow2"/>
      <source file="/var/lib/libvirt/images/pc-luks" index="6">
        <encryption format="luks">
          <secret type="passphrase" usage="luks"/>
        </encryption>
      </source>
      <backingStore/>
      <target dev="sda" bus="scsi"/>
      <alias name="scsi0-0-0-0"/>
      <address type="drive" controller="0" bus="0" target="0" unit="0"/>
    </disk>

3. Destroy and start vm, check the vm xml again
➜  ~ virsh destroy pc                           
Domain pc destroyed

➜  ~ virsh start pc
Domain pc started

➜  ~ virsh dumpxml pc | xmllint --xpath //disk -
<disk type="file" device="disk">
      <driver name="qemu" type="qcow2"/>
      <source file="/var/lib/libvirt/images/pc-luks" index="2"/>
      <backingStore/>
      <target dev="sda" bus="scsi"/>
      <encryption format="luks">
        <secret type="passphrase" usage="luks"/>
      </encryption>
      <alias name="scsi0-0-0-0"/>
      <address type="drive" controller="0" bus="0" target="0" unit="0"/>
    </disk>

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2020:2017