Mitigate potential range panic

[mariusvniekerk]

What type of PR is this?

/kind bug

What this PR does / why we need it:

When a podgroup has a MinMember set to 0 and no pods exist, the reconciler can encounter a range exception.

I have observed this on v0.26.7. The underlying code is still the same so it is likely the same weakness exists in the currently.

The crash appears as follows

panic: runtime error: index out of range [0] with length 0 [recovered]
	panic: runtime error: index out of range [0] with length 0

goroutine 227 [running]:
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Reconcile.func1()
	/go/src/sigs.k8s.io/scheduler-plugins/vendor/sigs.k8s.io/controller-runtime/pkg/internal/controller/controller.go:119 +0x1fa
panic({0x16c9880, 0xc0001dc000})
	/usr/local/go/src/runtime/panic.go:884 +0x212
sigs.k8s.io/scheduler-plugins/pkg/controllers.(*PodGroupReconciler).Reconcile(0xc000477d60, {0x1a1fbb8, 0xc0003cf230}, {{{0xc000a08378?, 0x10?}, {0xc0005010c0?, 0x40da67?}}})
	/go/src/sigs.k8s.io/scheduler-plugins/pkg/controllers/podgroup_controller.go:112 +0x9c6
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Reconcile(0x1a1fbb8?, {0x1a1fbb8?, 0xc0003cf230?}, {{{0xc000a08378?, 0x1567320?}, {0xc0005010c0?, 0x0?}}})
	/go/src/sigs.k8s.io/scheduler-plugins/vendor/sigs.k8s.io/controller-runtime/pkg/internal/controller/controller.go:122 +0xc8
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).reconcileHandler(0xc000422a00, {0x1a1fb10, 0xc0008a0c80}, {0x1634dc0?, 0xc000460020?})
	/go/src/sigs.k8s.io/scheduler-plugins/vendor/sigs.k8s.io/controller-runtime/pkg/internal/controller/controller.go:323 +0x38f
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).processNextWorkItem(0xc000422a00, {0x1a1fb10, 0xc0008a0c80})
	/go/src/sigs.k8s.io/scheduler-plugins/vendor/sigs.k8s.io/controller-runtime/pkg/internal/controller/controller.go:274 +0x1d9
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Start.func2.2()
	/go/src/sigs.k8s.io/scheduler-plugins/vendor/sigs.k8s.io/controller-runtime/pkg/internal/controller/controller.go:235 +0x85
created by sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Start.func2
	/go/src/sigs.k8s.io/scheduler-plugins/vendor/sigs.k8s.io/controller-runtime/pkg/internal/controller/controller.go:231 +0x333

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

NONE

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• ✅ login: mariusvniekerk / name: Marius van Niekerk (af11077)

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Hi @mariusvniekerk. Thanks for your PR.

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[APPROVALNOTIFIER] This PR is NOT APPROVED

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[Huang-Wei]

/ok-to-test

[Huang-Wei]

When a podgroup has a MinMember set to 0

I think we should always ensure the PodGroup's .minMember is greater than 0:

diff --git a/apis/scheduling/v1alpha1/types.go b/apis/scheduling/v1alpha1/types.go
index 86901dd5..8aaf6aa5 100644
--- a/apis/scheduling/v1alpha1/types.go
+++ b/apis/scheduling/v1alpha1/types.go
@@ -137,6 +137,7 @@ type PodGroupSpec struct {
 	// MinMember defines the minimal number of members/tasks to run the pod group;
 	// if there's not enough resources to start all tasks, the scheduler
 	// will not start anyone.
+	// +kubebuilder:validation:Minimum=1
 	MinMember int32 `json:"minMember,omitempty"`
 
 	// MinResources defines the minimal resource of members/tasks to run the pod group;

After that, run hack/update-codegen.sh to generate a new CRD manifest. (and also update manifests/coscheduling/crd.yaml manually)

[mariusvniekerk]

I think we should always ensure the PodGroup's .minMember is greater than 0:

I assumed that it could be validly be 0 if relying on .minResources instead.

[Huang-Wei]

I assumed that it could be validly be 0 if relying on .minResources instead.

IMHO, I think the case (0 .minMember along with non-empty .minResources) is not legit. Are you have some real-world usecase using this semantics?