slackhq/nebula · error

bad cpulist range

Error message

bad cpulist range %q

What it means

parseCPUList parses CPU list strings like "0-3,8" into individual CPU IDs. This error is returned when a range's end is less than its start (e.g. "5-2") or the range spans more than 8192 CPUs, which would produce an absurdly large allocation. It guards against malformed or pathological cpulist input.

Solutions

1. Fix the CPU list so each range's start is <= its end (e.g. change "10-4" to "4-10").
2. Split very large ranges into explicit lists or smaller ranges within the 8192-CPU span limit.
3. Validate the cpulist string before passing it in (check each range start <= end and span <= 8192).

Example fix

// before
parseCPUList("10-4") // error: bad cpulist range "10-4"
// after
parseCPUList("4-10") // [4,5,6,7,8,9,10]

func validateCPUList(s string) error {
    for _, part := range strings.Split(s, ",") {
        r := strings.SplitN(part, "-", 2)
        if len(r) == 2 {
            a, err1 := strconv.Atoi(strings.TrimSpace(r[0]))
            b, err2 := strconv.Atoi(strings.TrimSpace(r[1]))
            if err1 != nil || err2 != nil { return fmt.Errorf("bad entry %q", part) }
            if b < a { return fmt.Errorf("range start > end in %q", part) }
            if b-a > 8192 { return fmt.Errorf("range too large in %q", part) }
        }
    }
    return nil
}

cpus, err := parseCPUList(flagValue)
if err != nil {
    return fmt.Errorf("invalid -cpulist %q: %w", flagValue, err)
}

When it happens

Trigger: Calling parseCPUList (directly, or via byIntelCoreMask or numaNodes) with a range token where b < a, e.g. "10-4", or a span b-a > 8192, e.g. "0-99999".

Common situations: Hand-edited CPU affinity settings in config (cpuset, taskset-style strings), environment-specific NUMA parsing on unusual hardware, typos reversing range endpoints, or hostile/garbage input to configuration parsers.

Related errors

• appears to be a range but could not be parsed;
• could not parse rule
• ErrBadFormat
• ErrInvalidLocalIP
• ErrNoCredential

AI-assisted analysis of slackhq/nebula@dd8f660c0a (2026-09-03). Data as JSON: /api/errors/f0ed5cd6d566271c. Report an issue: GitHub.

Appendix: source

Thrown at cpupick/perf_linux.go:139

		part = strings.TrimSpace(part)
		if part == "" {
			continue
		}
		lo, hi, isRange := strings.Cut(part, "-")
		a, err := strconv.Atoi(lo)
		if err != nil {
			return nil, fmt.Errorf("bad cpulist entry %q: %w", part, err)
		}
		if !isRange {
			out = append(out, a)
			continue
		}
		b, err := strconv.Atoi(hi)
		if err != nil {
			return nil, fmt.Errorf("bad cpulist entry %q: %w", part, err)
		}
		if b < a || b-a > 8192 {
			return nil, fmt.Errorf("bad cpulist range %q", part)
		}
		for v := a; v <= b; v++ {
			out = append(out, v)
		}
	}
	return out, nil
}

func readIntFile(path string) (int, error) {
	b, err := os.ReadFile(path)
	if err != nil {
		return 0, err
	}
	return strconv.Atoi(strings.TrimSpace(string(b)))
}

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