[Cherry-pick 1.12] Fix scheduler panic by moving InitKubeSchedulerRelatedMetrics outside…

[JesseStutler]

Cherry-picks #4731 for release-1.12.

What type of PR is this?

Bug fix

What this PR does / why we need it:

Scheduler panics with nil pointer dereference during pod scheduling when started without --enable-metrics=true. The Kubernetes scheduler framework plugins unconditionally access k8smetrics.Goroutines, which was only initialized when metrics were enabled.

Changes:

• Moved metrics.InitKubeSchedulerRelatedMetrics() outside the if opt.EnableMetrics || opt.EnablePprof block in cmd/scheduler/app/server.go
• Ensures k8smetrics.Goroutines is always initialized before scheduler starts

// Before: InitKubeSchedulerRelatedMetrics only called when metrics enabled
if opt.EnableMetrics || opt.EnablePprof {
    metrics.InitKubeSchedulerRelatedMetrics()
    go startMetricsServer(opt)
}

// After: Always initialize required metrics
metrics.InitKubeSchedulerRelatedMetrics()

if opt.EnableMetrics || opt.EnablePprof {
    go startMetricsServer(opt)
}

Which issue(s) this PR fixes:

Fixes #4729

Special notes for your reviewer:

The panic occurs in k8s.io/kubernetes/pkg/scheduler/framework/parallelize.Parallelizer.Until at line 57 when calling Goroutines.WithLabelValues(). This metric must be initialized regardless of whether metrics export is enabled.

Does this PR introduce a user-facing change?

release-note Fix scheduler panic when starting without --enable-metrics=true flag

[gemini-code-assist]

Summary of Changes

Hello @JesseStutler, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical bug in the Kubernetes scheduler where it would panic due to a nil pointer dereference if started without metrics enabled. The fix involves a minor but crucial change to the scheduler's initialization logic, ensuring that a specific metrics-related function is always invoked. This guarantees that essential metrics components are properly set up, thereby preventing the panic and enhancing the scheduler's robustness and reliability under various configuration settings.

Highlights

• Bug Fix: Resolves a nil pointer dereference panic in the Kubernetes scheduler that occurred when the scheduler was started without the --enable-metrics=true flag.
• Metrics Initialization: Ensures that metrics.InitKubeSchedulerRelatedMetrics() is always called during scheduler startup, regardless of whether metrics export or pprof are enabled.
• Dependency Resolution: Guarantees that k8smetrics.Goroutines, which is unconditionally accessed by scheduler framework plugins, is properly initialized to prevent runtime errors.

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[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please assign wpeng102 for approval. For more information see the Kubernetes Code Review Process.

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[gemini-code-assist]

Code Review

This pull request correctly fixes a scheduler panic that occurs when metrics are disabled. The issue is caused by an uninitialized metric variable that is used by the Kubernetes scheduler framework. The fix moves the metric initialization outside of the conditional block, ensuring it always runs. The change is correct and effectively resolves the bug. I have added one suggestion to improve the clarity of the comment accompanying the fix, making it more explicit about why this initialization is critical.

[hajnalmt]

/lgtm