cl_sub_dio_alloc() intentionally permits sub-DIO requests without a duplicated iterator vector. In particular, XARRAY and DISC discard iterators do not require id_vec duplication:

/* xarray and discard do not need vec to be dup'd */
if (!v_sz)
  goto out; 

However, the normal completion path unconditionally frees the duplicate state:

cl_sub_dio_end()
  -> csd_dup_free()
  -> OBD_FREE(tmp, ...) 

csd_dup_free() currently assumes dup->id_vec is non-NULL. This triggers the OBD_FREE() assertion when completion reaches a valid vectorless sub-DIO request.The issue was exposed while running Lustre client tests on Ubuntu 24 ARM64 with Linux 6.17, but the same alloc/free mismatch exists in current lustre-master