Hi Bence,

NOTE: This is more of a glance issue than cinder as the changes made are part of glance cinder store.

I did the same image save operation 10 times concurrently and was able to save all 10 images successfully.

stack@devstack-VirtualBox:~/devstack$ glance image-download 18dc5568-1a47-44ff-a724-5ef8d44d9e08 --file one.qcow2; glance image-download 18dc5568-1a47-44ff-a724-5ef8d44d9e08 --file two.qcow2; glance image-download 18dc5568-1a47-44ff-a724-5ef8d44d9e08 --file three.qcow2; glance image-download 18dc5568-1a47-44ff-a724-5ef8d44d9e08 --file four.qcow2; glance image-download 18dc5568-1a47-44ff-a724-5ef8d44d9e08 --file five.qcow2; glance image-download 18dc5568-1a47-44ff-a724-5ef8d44d9e08 --file six.qcow2; glance image-download 18dc5568-1a47-44ff-a724-5ef8d44d9e08 --file seven.qcow2; glance image-download 18dc5568-1a47-44ff-a724-5ef8d44d9e08 --file eight.qcow2; glance image-download 18dc5568-1a47-44ff-a724-5ef8d44d9e08 --file nine.qcow2; glance image-download 18dc5568-1a47-44ff-a724-5ef8d44d9e08 --file ten.qcow2;

stack@devstack-VirtualBox:~/devstack$ ll *.qcow2
-rw-rw-r-- 1 stack stack 16300544 Apr 18 14:20 eight.qcow2
-rw-rw-r-- 1 stack stack 16300544 Apr 18 14:19 five.qcow2
-rw-rw-r-- 1 stack stack 16300544 Apr 18 14:19 four.qcow2
-rw-rw-r-- 1 stack stack 16300544 Apr 18 14:21 nine.qcow2
-rw-rw-r-- 1 stack stack 16300544 Apr 18 14:17 one.qcow2
-rw-rw-r-- 1 stack stack 16300544 Apr 18 14:20 seven.qcow2
-rw-rw-r-- 1 stack stack 16300544 Apr 18 14:19 six.qcow2
-rw-rw-r-- 1 stack stack 16300544 Apr 18 14:21 ten.qcow2
-rw-rw-r-- 1 stack stack 16300544 Apr 18 14:18 three.qcow2
-rw-rw-r-- 1 stack stack 16300544 Apr 18 14:18 two.qcow2

Glance image:

stack@devstack-VirtualBox:~/devstack$ glance image-show 18dc5568-1a47-44ff-a724-5ef8d44d9e08
+------------------+----------------------------------------------------------------------------------+
| Property         | Value                                                                            |
+------------------+----------------------------------------------------------------------------------+
| checksum         | b874c39491a2377b8490f5f1e89761a4                                                 |
| container_format | bare                                                                             |
| created_at       | 2022-04-18T08:14:24Z                                                             |
| direct_url       | cinder://lvmdriver-1/8851784d-5bef-4379-8c37-dd178fff8e37                        |
| disk_format      | qcow2                                                                            |
| id               | 18dc5568-1a47-44ff-a724-5ef8d44d9e08                                             |
| locations        | [{"url": "cinder://lvmdriver-1/8851784d-5bef-4379-8c37-dd178fff8e37",            |
|                  | "metadata": {"store": "lvmdriver-1"}}]                                           |
| min_disk         | 0                                                                                |
| min_ram          | 0                                                                                |
| name             | test-2-multiattach-lvm                                                           |
| os_hash_algo     | sha512                                                                           |
| os_hash_value    | 6b813aa46bb90b4da216a4d19376593fa3f4fc7e617f03a92b7fe11e9a3981cbe8f0959dbebe3622 |
|                  | 5e5f53dc4492341a4863cac4ed1ee0909f3fc78ef9c3e869                                 |
| os_hidden        | False                                                                            |
| owner            | e01f8d1cdb6f4e0a85fa76286928060c                                                 |
| protected        | False                                                                            |
| size             | 16300544                                                                         |
| status           | active                                                                           |
| stores           | lvmdriver-1                                                                      |
| tags             | []                                                                               |
| updated_at       | 2022-04-18T08:14:45Z                                                             |
| virtual_size     | 117440512                                                                        |
| visibility       | shared                                                                           |
+------------------+----------------------------------------------------------------------------------+


Image-volume

stack@devstack-VirtualBox:~/devstack$ cinder list --all
+--------------------------------------+----------------------------------+-----------+--------------------------------------------+------+-----------------+----------+-------------+
| ID                                   | Tenant ID                        | Status    | Name                                       | Size | Volume Type     | Bootable | Attached to |
+--------------------------------------+----------------------------------+-----------+--------------------------------------------+------+-----------------+----------+-------------+
| 515654c6-e42a-4ae1-9c40-41f24fa6b567 | 860424c7e36b4129bb55ab6a5e1ec76e | available | image-0407bb90-968c-4341-be65-6c4673dcca5e | 1    | lvm-multiattach | false    |             |
| 8851784d-5bef-4379-8c37-dd178fff8e37 | 860424c7e36b4129bb55ab6a5e1ec76e | available | image-18dc5568-1a47-44ff-a724-5ef8d44d9e08 | 1    | lvm-multiattach | false    |             | -- image-volume containing the image
| bffdffff-6943-483c-8315-3c8b9fe1e407 | 860424c7e36b4129bb55ab6a5e1ec76e | available | image-6a2ea172-630b-4877-8a5f-f310aecf3060 | 1    | lvmdriver-1     | false    |             |
+--------------------------------------+----------------------------------+-----------+--------------------------------------------+------+-----------------+----------+-------------+