Fix critical logic bug in change detection

The post_save handler was comparing identical values so changes were never detected.
Split into pre_save (store original) and post_save (compare & invalidate) handlers.
Also added .only('id') optimization and SoftTimeLimitExceeded handling as suggested.

Author: Srinath0916

openwisp_controller/config/apps.py

@@ -273,7 +273,8 @@ def enable_cache_invalidation(self):
             device_cache_invalidation_handler,
             devicegroup_change_handler,
             devicegroup_delete_handler,
-            organization_config_settings_change_handler,
+            organization_config_settings_pre_save_handler,
+            organization_config_settings_post_save_handler,
             vpn_server_change_handler,
         )
 
@@ -340,8 +341,13 @@ def enable_cache_invalidation(self):
             sender=self.vpn_model,
             dispatch_uid="vpn.invalidate_checksum_cache",
         )
+        pre_save.connect(
+            organization_config_settings_pre_save_handler,
+            sender=self.organization_config_settings_model,
+            dispatch_uid="organization_config_settings.store_original_context",
+        )
         post_save.connect(
-            organization_config_settings_change_handler,
+            organization_config_settings_post_save_handler,
             sender=self.organization_config_settings_model,
             dispatch_uid="organization_config_settings.invalidate_vpn_cache",
         )

openwisp_controller/config/handlers.py

@@ -154,21 +154,27 @@ def organization_disabled_handler(instance, **kwargs):
     tasks.invalidate_controller_views_cache.delay(str(instance.id))
 
 
-def organization_config_settings_change_handler(instance, **kwargs):
+def organization_config_settings_pre_save_handler(instance, **kwargs):
     """
-    Invalidates VPN cache when OrganizationConfigSettings context changes.
+    Stores original context before save to detect changes.
     """
     if instance._state.adding:
         return
-
-    # Check if context actually changed
     try:
         db_instance = instance.__class__.objects.only("context").get(id=instance.id)
-        if db_instance.context != instance.context:
-            transaction.on_commit(
-                lambda: tasks.invalidate_organization_vpn_cache.delay(
-                    str(instance.organization_id)
-                )
-            )
+        instance._original_context = db_instance.context
     except instance.__class__.DoesNotExist:
-        pass
+        instance._original_context = None
+
+
+def organization_config_settings_post_save_handler(instance, **kwargs):
+    """
+    Invalidates VPN cache when OrganizationConfigSettings context changes.
+    """
+    original_context = getattr(instance, "_original_context", None)
+    if original_context is not None and original_context != instance.context:
+        transaction.on_commit(
+            lambda: tasks.invalidate_organization_vpn_cache.delay(
+                str(instance.organization_id)
+            )
+        )

openwisp_controller/config/tasks.py

@@ -109,9 +109,17 @@ def invalidate_organization_vpn_cache(organization_id):
     Vpn = load_model("config", "Vpn")
     from .controller.views import GetVpnView
 
-    for vpn in Vpn.objects.filter(organization_id=organization_id).iterator():
-        GetVpnView.invalidate_get_vpn_cache(vpn)
-        vpn.invalidate_checksum_cache()
+    try:
+        for vpn in (
+            Vpn.objects.filter(organization_id=organization_id).only("id").iterator()
+        ):
+            GetVpnView.invalidate_get_vpn_cache(vpn)
+            vpn.invalidate_checksum_cache()
+    except SoftTimeLimitExceeded:
+        logger.error(
+            "soft time limit hit while executing "
+            f"invalidate_organization_vpn_cache for organization {organization_id}"
+        )
 
 
 @shared_task(soft_time_limit=7200)