When migrate vm and vm’s disks target host qemu crash due to an invalid free.

#0 object_unref (obj=0x1000) at /qemu-2.12/rpmbuild/BUILD/qemu-2.12/qom/object.c:920

#1 0x0000560434d79e79 in memory_region_unref (mr=<optimized out>)

at /qemu-2.12/rpmbuild/BUILD/qemu-2.12/memory.c:1730

#2 flatview_destroy (view=0x560439653880) at /qemu-2.12/rpmbuild/BUILD/qemu-2.12/memory.c:292

#3 0x000056043514dfbe in call_rcu_thread (opaque=<optimized out>)

at /qemu-2.12/rpmbuild/BUILD/qemu-2.12/util/rcu.c:284

#4 0x00007fbc2b36fe25 in start_thread () from /lib64/libpthread.so.0

#5 0x00007fbc2b099bad in clone () from /lib64/libc.so.6

test base qemu-2.12.0，but use lastest qemu(v6.0.0-rc2) also reproduce.

As follow patch can resolve this problem:

https://lists.gnu.org/archive/html/qemu-devel/2018-07/msg02272.html

Steps to reproduce:

(1) Create VM (virsh define)

(2) Add 64 virtio scsi disks

(3) migrate vm and vm’disks

-------------------------------------------------------------------------------------------------------------------------------------
本邮件及其附件含有新华三集团的保密信息，仅限于发送给上面地址中列出
的个人或群组。禁止任何其他人以任何形式使用（包括但不限于全部或部分地泄露、复制、
或散发）本邮件中的信息。如果您错收了本邮件，请您立即电话或邮件通知发件人并删除本
邮件！
This e-mail and its attachments contain confidential information from New H3C, which is
intended only for the person or entity whose address is listed above. Any use of the
information contained herein in any way (including, but not limited to, total or partial
disclosure, reproduction, or dissemination) by persons other than the intended
recipient(s) is prohibited. If you receive this e-mail in error, please notify the sender
by phone or email immediately and delete it!