Fix GC uid races and handling of conflicting ownerReferences #92743

Before deleting an object based on absent owners, GC verifies absence of those owners with a live lookup. The coordinates used to perform that live lookup are the ones specified in the ownerReference of the child. In order to performantly delete multiple children from the same parent (e.g. 1000 pods from a replicaset), a 404 response to a lookup is cached in absentOwnerCache. Previously, the cache was a simple uid set. However, since children can disagree on the coordinates that should be used to look up a given uid, the cache should record the exact coordinates verified absent. This is a [apiVersion, kind, namespace, name, uid] tuple.

Virtual nodes can be added to the GC graph in order to represent objects which have not been observed via an informer, but are referenced via ownerReferences. These virtual nodes are requeued into attemptToDelete until they are observed via an informer, or successfully verified absent via a live lookup. Previously, both of those code paths called markObserved() to stop requeuing into attemptToDelete. Because it is useful to know whether a particular node has been observed via a real informer event, this commit does the following: * adds a `virtual bool` attribute to graph events so we know which ones came from a real informer * limits the markObserved() call to the code path where a real informer event is observed * uses an alternative mechanism to stop requeueing into attemptToDelete when a virtual node is verified absent via a live lookup

If the graph contains a virtual node (because some child object referenced it in an OwnerRef), and a real informer event is observed for that uid at different coordinates, we want to fix the coordinates of the node in the graph to match the actual coordinates. The safe way to do this is to clone the node, replace the identity in the clone, then replace the node with the clone. Modifying the identity directly is not safe because it is accessed lock-free from many code paths. Replacing the node in the graph from processGraphChanges is safe because it is the only graph writer.

… or observed Virtual nodes are added to the attemptToDelete queue, and continue getting requeued until they are successfully verified absent or are observed via informer. In the meantime, if the real object associated with that UID is observed via informer, or is observed to be deleted via informer, the graph node for that UID can be removed or marked as observed. In that case, we should stop retrying to get the virtual node coordinates.

…tch observed parent coordinates When adding a dependent to the graph, we ensure there is a node representing each owner reference, and add the dependent to each parent node. If the parent node already exists, and the dependent's ownerReference coordinates disagree with the verified coordinates, add the dependent to the attemptToDelete queue. This queue will check the dependent's ownerReferences using the coordinates specified by the dependent. If all of the owners can be verified absent, the dependent will be deleted. If some are still present, or if there are errors looking them up, the dependent will not be deleted. If the parent node has been observed via informer event (so we know the coordinates are accurate), and the verified owner is namespaced, and the dependent is not in the same namespace, an event will be recorded for user visibility, since cross-namespace ownerReferences are not supported.

…inates If a virtual delete event is received for a node whose dependents disagree on the parent's coordinates: 1. propagate the delete to children that matched the verified absent coordinates 2. if the existing node is virtual, select a new set of coordinates from the remaining dependents 3. do not delete the parent node from the graph if the parent node is non-virtual, or if there are dependents that do not agree with the virtual delete event coordinates

…d as observed When we observe valid coordinates for a previously virtual node, if there are dependents that do not agree with those coordinates, add them to the attemptToDelete queue. This queue will check the dependent's ownerReferences using the coordinates specified by the dependent. If all of the owners can be verified absent, the dependent will be deleted. If some are still present, or if there are errors looking them up, the dependent will not be deleted. If the verified owner is namespaced, and the dependent is not in the same namespace, an event will be recorded for user visibility, since cross-namespace ownerReferences are not supported.

…ng lookups forever If a cluster-scoped dependent references a namespace-scoped owner, this is an invalid relationship, and the lookup will never succeed in attemptToDelete. Short-circuit requeueing in attemptToDelete and log.

Adds unit tests covering the problematic scenarios identified around conflicting data in child owner references Before After package level 51% 68% garbagecollector.go 60% 75% graph_builder.go 50% 81% graph.go 50% 68% Added/improved coverage of key functions that had lacking unit test coverage: * attemptToDeleteWorker * attemptToDeleteItem * processGraphChanges (added coverage of all added code)

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Fix GC uid races and handling of conflicting ownerReferences #92743

Fix GC uid races and handling of conflicting ownerReferences #92743

Commits on Nov 17, 2020