Move management over effective service levels from `service_level_controller`
to a new dedicated type -- `auth_integration`.
Before these changes, it was possible for the service level controller to try
to access `auth::service` after it was deinitialized. For instance, it could
happen when reloading the cache. That HAS happened as described in the following
issue: scylladb/scylladb#24792.
Although the problem might have been mitigated or even resolved in
scylladb/scylladb@10214e13bd, it's not clear
how the service will be used in the future. It's best to prevent similar bugs
than trying to fix them later on.
The logic responsible for preventing to access an uninitialized `auth::service`
was also either non-existent, complex, or non-sufficient.
To prevent accessing `auth::service` by the service level controller, we extract
the relevant portion of the code to a separate entity -- `auth_integration`.
It's an internal helper type whose sole purpose is to manage effective service
levels.
Thanks to that, we were able to nest the lifetime of `auth_integration` within
the lifetime of `auth::service`. It's now impossible to attempt to dereference
it while it's uninitialized.
If a bug related to an invalid access is spotted again, though, it might also
be easier to debug it now.
There should be no visible change to the users of the interface of the service
level controller. We strived to make the patch minimal, and the only affected
part of the logic should be related to how `auth::service` is accessed.
The relevant portion of the initialization and deinitialization flow:
(a) Before the changes:
1. Initialize `service_level_controller`. Pass a reference to an uninitialized
`auth::service` to it.
2. Initialize other services.
3. Initialize and start `auth::service`.
4. (work)
5. Stop and deinitialize `auth::service`.
6. Deinitialize other services.
7. Deinitialize `service_level_controller`.
(b) After the changes:
1. Initialize `service_level_controller`. Pass a reference to an uninitialized
`auth::service` to it. (*)
2. Initialize other services.
3. Initialize and start `auth::service`.
4. Initialize `auth_integration`. Register it in `service_level_controller`.
5. (work)
6. Unregister `auth_integration` in `service_level_controller` and deinitialize
it.
7. Stop and deinitialize `auth::service`.
8. Deinitialize other services.
9. Deinitialize `service_level_controller`.
(*):
The reference to `auth::service` in `service_level_controller` is still
necessary. We need to access the service when dropping a distributed
service level.
Although it would be best to cut that link between the service level
controller and `auth::service` too, effectively separating the entities,
it would require more work, so we leave it as-is for now.
It shouldn't prove problematic as far as accessing an uninitialized service
goes. Trying to drop a service level at the point when we're de-initializing
auth should be impossible.
For more context, see the function `drop_distributed_service_level` in
`service_level_controller`.
A trivial test has been included in the PR. Although its value is questionable
as we only try to reload the service level cache at a specific moment, it's
probably the best we can deliver to provide a reproducer of the issue this patch
is resolving.
Fixesscylladb/scylladb#24792
Backport: The impact of the bug was minimal as it only affected the shutdown.
However, since CI is failing because of it, let's backport the change to all
supported versions.
- (cherry picked from commit 7d0086b093)
- (cherry picked from commit 34afb6cdd9)
- (cherry picked from commit e929279d74)
- (cherry picked from commit dd5a35dc67)
- (cherry picked from commit fc1c41536c)
Parent PR: #25478Closesscylladb/scylladb#25753
* github.com:scylladb/scylladb:
service/qos: Move effective SL cache to auth_integration
service/qos: Add auth::service to auth_integration
service/qos: Reload effective SL cache conditionally
service/qos: Add gate to auth_integration
service/qos: Introduce auth_integration
1c8e10231a