### Steps to reproduce

* Begin of the insertionCreate 3End of the insertion Begin of the deletion Unclear. Probably a largerEnd of the deletion work Begin of the insertionpackages: 1 parent and 2 children.End of the insertion Begin of the deletion package graph with a deep hierarchyEnd of the deletion

* Begin of the insertionGo toEnd of the insertion Begin of the deletion Artificial one using the console

* Create 439 (might be OS dependant)End of the deletion work packages Begin of the insertionlist view

End of the insertion Begin of the deletion where each work package is the child of the one created before (resulting in a tree with the breadth of 1) e.g. by using something like (in the console): `439.times { User.execute_as(author) { WorkPackage.new(subject: "A subject", project:, priority:, type:, status:, author:, parent: WorkPackage.last).save! } }`

End of the deletion * Begin of the insertionUseEnd of the insertion Begin of the deletion Go toEnd of the deletion the Begin of the insertionleft handle onEnd of the insertion Begin of the deletion topmost work package ofEnd of the deletion the Begin of the insertionparent and drag&drop it between the 2 children

End of the insertion Begin of the deletion just created ones.

End of the deletion * Begin of the insertionThis will try to set itself as a parentEnd of the insertion Begin of the deletion Open its date picker

* Click on "Automatic" scheduling modeEnd of the deletion


### What is the buggy behavior?

* Begin of the insertionError 500 after 30 seconds of lag.End of the insertion Begin of the deletion Unclear. Probably, the scheduling failed.End of the deletion

* Begin of the insertionIt tries to set itself as a parent (or as a child, it depends how you see things), and somewhere inEnd of the insertion Begin of the deletion ForEnd of the deletion the Begin of the insertionprocess, it tries to compute some scheduling information which leads to an endless loop (trying to find its ancestors) which ultimately leads to a SystemStackError and a 500.


End of the insertion Begin of the deletion artificial one

* An error is shown


End of the deletion ### What is the expected behavior?

* Begin of the insertionDrag and dropping a parent to make it a child of itself should be prohibited, or detected early.End of the insertion Begin of the deletion No errorEnd of the deletion


### Begin of the insertion**Screenshots**

A video recording demonstrating the issue is attached to this bug.

###End of the insertion **Logs**

Begin of the insertionThis has been seen on AppSignal:

End of the insertion * [https://appsignal.com/openproject-gmbh/sites/674718f1d2a5e4a7cb8b2298/exceptions/incidents/1024](https://appsignal.com/openproject-gmbh/sites/674718f1d2a5e4a7cb8b2298/exceptions/incidents/1024)

* [https://appsignal.com/openproject-gmbh/sites/674718f1d2a5e4a7cb8b2298/exceptions/incidents/969](https://appsignal.com/openproject-gmbh/sites/674718f1d2a5e4a7cb8b2298/exceptions/incidents/969)

* [https://appsignal.com/openproject-gmbh/sites/673c8be183eb67dcd6c4e75d/exceptions/incidents/1177](https://appsignal.com/openproject-gmbh/sites/673c8be183eb67dcd6c4e75d/exceptions/incidents/1177)

* https://appsignal.com/openproject-gmbh/sites/673c8be183eb67dcd6c4e75d/exceptions/incidents/1176


```text
app/services/work_packages/schedule_dependency.rb:122 Array#each
app/services/work_packages/schedule_dependency.rb:122 Enumerable#flat_map
app/services/work_packages/schedule_dependency.rb:122 WorkPackages::ScheduleDependency#descendants
app/services/work_packages/schedule_dependency.rb:122 block in WorkPackages::ScheduleDependency#descendants
app/services/work_packages/schedule_dependency.rb:122 Array#each
app/services/work_packages/schedule_dependency.rb:122 Enumerable#flat_map
app/services/work_packages/schedule_dependency.rb:122 WorkPackages::ScheduleDependency#descendants
app/services/work_packages/schedule_dependency.rb:122 block in WorkPackages::ScheduleDependency#descendants
app/services/work_packages/schedule_dependency.rb:122 Array#each
app/services/work_packages/schedule_dependency.rb:122 Enumerable#flat_map
app/services/work_packages/schedule_dependency.rb:122 WorkPackages::ScheduleDependency#descendants
app/services/work_packages/schedule_dependency.rb:122 block in WorkPackages::ScheduleDependency#descendants
app/services/work_packages/schedule_dependency.rb:122 Array#each
app/services/work_packages/schedule_dependency.rb:122 Enumerable#flat_map
app/services/work_packages/schedule_dependency.rb:122 WorkPackages::ScheduleDependency#descendants
app/services/work_packages/schedule_dependency.rb:122 block in WorkPackages::ScheduleDependency#descendants
app/services/work_packages/schedule_dependency.rb:122 Array#each
app/services/work_packages/schedule_dependency.rb:122 Enumerable#flat_map
app/services/work_packages/schedule_dependency.rb:122 WorkPackages::ScheduleDependency#descendants
app/services/work_packages/schedule_dependency.rb:122 block in WorkPackages::ScheduleDependency#descendants
app/services/work_packages/schedule_dependency.rb:122 Array#each
app/services/work_packages/schedule_dependency.rb:122 Enumerable#flat_map
app/services/work_packages/schedule_dependency.rb:122 WorkPackages::ScheduleDependency#descendants
app/services/work_packages/schedule_dependency.rb:122 block in WorkPackages::ScheduleDependency#descendants
app/services/work_packages/schedule_dependency.rb:122 Array#each
app/services/work_packages/schedule_dependency.rb:122 Enumerable#flat_map
app/services/work_packages/schedule_dependency.rb:122 WorkPackages::ScheduleDependency#descendants
app/services/work_packages/schedule_dependency.rb:122 block in WorkPackages::ScheduleDependency#descendants
app/services/work_packages/schedule_dependency.rb:122 Array#each
app/services/work_packages/schedule_dependency.rb:122 Enumerable#flat_map
app/services/work_packages/schedule_dependency.rb:122 WorkPackages::ScheduleDependency#descendants
app/services/work_packages/schedule_dependency.rb:122 block in WorkPackages::ScheduleDependency#descendants
... Begin of the insertion
app/services/work_packages/schedule_dependency.rb:122:in 'block in WorkPackages::ScheduleDependency#descendants'
app/services/work_packages/schedule_dependency.rb:122:in 'Array#each'
app/services/work_packages/schedule_dependency.rb:122:in 'Enumerable#flat_map'
app/services/work_packages/schedule_dependency.rb:122:in 'WorkPackages::ScheduleDependency#descendants'
app/services/work_packages/schedule_dependency/dependency.rb:81:in 'WorkPackages::ScheduleDependency::Dependency#descendants'
app/services/work_packages/schedule_dependency/dependency.rb:85:in 'WorkPackages::ScheduleDependency::Dependency#alive_descendants'
app/services/work_packages/schedule_dependency/dependency.rb:71:in 'WorkPackages::ScheduleDependency::Dependency#has_descendants?'
app/services/work_packages/set_schedule_service.rb:111:in 'WorkPackages::SetScheduleService#reschedule'
app/services/work_packages/set_schedule_service.rb:88:in 'block in WorkPackages::SetScheduleService#schedule_following'
app/services/work_packages/schedule_dependency.rb:62:in 'block in WorkPackages::ScheduleDependency#in_schedule_order'
app/services/work_packages/schedule_dependency.rb:61:in 'Array#each'
app/services/work_packages/schedule_dependency.rb:61:in 'WorkPackages::ScheduleDependency#in_schedule_order'
app/services/work_packages/set_schedule_service.rb:85:in 'WorkPackages::SetScheduleService#schedule_following'
app/services/work_packages/set_schedule_service.rb:43:in 'WorkPackages::SetScheduleService#call'
app/services/work_packages/set_attributes_service.rb:292:in 'WorkPackages::SetAttributesService#update_dates_from_rescheduled_children'
app/services/work_packages/set_attributes_service.rb:275:in 'WorkPackages::SetAttributesService#update_dates'
app/services/work_packages/set_attributes_service.rb:70:in 'WorkPackages::SetAttributesService#set_calculated_attributes'
app/services/work_packages/set_attributes_service.rb:44:in 'block in WorkPackages::SetAttributesService#set_attributes'
lib/open_project/changed_by_system.rb:87:in 'OpenProject::ChangedBySystem#change_by_system'
app/services/work_packages/set_attributes_service.rb:43:in 'WorkPackages::SetAttributesService#set_attributes'
modules/backlogs/lib/open_project/backlogs/patches/set_attributes_service_patch.rb:36:in 'OpenProject::Backlogs::Patches::SetAttributesServicePatch::InstanceMethods#set_attributes'
app/services/base_services/set_attributes.rb:44:in 'BaseServices::SetAttributes#perform'
app/services/base_services/base_callable.rb:40:in 'block in BaseServices::BaseCallable#call'
app/services/concerns/with_reversible_state.rb:53:in 'BaseServices::BaseCallable#assign_state'
app/services/base_services/base_callable.rb:39:in 'BaseServices::BaseCallable#call'
app/services/base_services/write.rb:60:in 'BaseServices::Write#set_attributes'
app/services/attachments/replace_attachments.rb:37:in 'WorkPackages::UpdateService#set_attributes'
app/services/base_services/write.rb:51:in 'BaseServices::Write#before_perform'
app/services/base_services/base_contracted.rb:61:in 'block in BaseServices::BaseContracted#perform'
app/models/journal/notification_configuration.rb:62:in 'Journal::NotificationConfiguration.with_first'
app/models/journal/notification_configuration.rb:45:in 'Journal::NotificationConfiguration.with'
app/services/shared/service_context.rb:67:in 'block in Shared::ServiceContext#without_context_transaction'
lib/open_project/locale_helper.rb:36:in 'OpenProject::LocaleHelper.with_locale_for'
app/models/user.rb:538:in 'User.execute_as'
app/services/shared/service_context.rb:66:in 'Shared::ServiceContext#without_context_transaction'
app/services/shared/service_context.rb:45:in 'block in Shared::ServiceContext#in_mutex_context'
lib/open_project/mutex.rb:71:in 'block in OpenProject::Mutex.with_advisory_lock'
lib/open_project/mutex.rb:69:in 'OpenProject::Mutex.with_advisory_lock'
lib/open_project/mutex.rb:63:in 'block in OpenProject::Mutex.with_advisory_lock_transaction'
lib/open_project/mutex.rb:62:in 'OpenProject::Mutex.with_advisory_lock_transaction'
app/services/shared/service_context.rb:44:in 'Shared::ServiceContext#in_mutex_context'
app/services/shared/service_context.rb:35:in 'Shared::ServiceContext#in_context'
app/services/base_services/base_contracted.rb:54:in 'BaseServices::BaseContracted#service_context'
app/services/base_services/base_contracted.rb:59:in 'BaseServices::BaseContracted#perform'
app/services/base_services/base_callable.rb:40:in 'block in BaseServices::BaseCallable#call'
app/services/concerns/with_reversible_state.rb:53:in 'BaseServices::BaseCallable#assign_state'
app/services/base_services/base_callable.rb:39:in 'BaseServices::BaseCallable#call'
lib/api/utilities/endpoints/bodied.rb:117:in 'API::Utilities::Endpoints::Bodied#process'
lib/api/utilities/endpoints/bodied.rb:90:in 'block in mount'End of the insertion
```