[bug] Background task update_config launched multiple times

[nemesifier]

There's an easy way I can trigger this on the current master:

In the device change page, make sure to have multiple templates, then edit one of the default values provided by templates in the config variable section, even if they're not used in the config.

In the celery worker I see:

[2025-09-24 00:49:27,262: INFO/MainProcess] Task openwisp_controller.connection.tasks.update_config[c0b37457-d389-48cf-b875-cc85b18fca66] received
[2025-09-24 00:49:27,263: INFO/MainProcess] Task openwisp_controller.connection.tasks.update_config[2a9a4b45-a9a8-43bc-ab5b-b2852e3c41ca] received
[2025-09-24 00:49:27,267: INFO/MainProcess] Task openwisp_controller.connection.tasks.update_config[fb23b160-7d21-4487-91e8-3b39ab404e50] received

Sometimes I see it up to 4 times.

I've observed this in prod too by witnessing multiple SSH connection to a device by looking at the syslog output via logread on OpenWrt.

Recommendation

Let's work on this as a follow up of #1124, let's make sure that the config_modified_signal is only sent when the checksum changes and make sure is only sent once.

Let's double check different ways of changing the config and ensure there's a test for each which asserts the config_modified signal is sent only once:

• Base assumptions for all the tests: one device with at least 2 templates using default variables, have 1 variable not being used
• Admin: change a device: config and templates
• Admin: change a template
• REST APÎ: change a device: config and templates
• REST API: change a template

[pandafy]

This bug only appears when the user makes changes to the Device.Config using the Django admin.

The sorted-m2m field clears the config.templates field and then adds the template back. This operation executes the following code

openwisp-controller/openwisp_controller/config/base/config.py

Lines 273 to 282 in aa3189f

	with transaction.atomic():
	# do not send config modified signal if
	# config instance has just been created
	if not instance._just_created:
	# sends only config modified signal
	instance._send_config_modified_signal(action="m2m_templates_changed")
	if instance.status != "modified":
	# sends both status modified and config modified signals
	instance.set_status_modified(send_config_modified_signal=False)