STRUCT CPUHP_STEP(9)

✨ struct cpuhp_step(9) ✨

okay so bestie, welcome to the Kernel API Manual 💅 we're looking at struct cpuhp_step(9) and honestly? it's giving main character energy in the CPU hotplug world. 🫶

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🌸 NAME 🌸

struct cpuhp_step — the Hotplug state machine step ✨ lowkey the little building block that makes the whole hotplug dance work, no cap.

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🦋 SYNOPSIS 🦋

struct cpuhp_step {
    const char              *name;
    union {
      int (*single)(unsigned int cpu);
      int (*multi)(unsigned int cpu, struct hlist_node *node);
    } startup;
    union {
      int (*single)(unsigned int cpu);
      int (*multi)(unsigned int cpu, struct hlist_node *node);
    } teardown;
    bool cant_stop;
    bool multi_instance;
 };

like, that's the whole vibe right there ⬆️ copy it exactly, don't come for me 🙈

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🎀 Members 🎀

• name — the name of the step, literally its whole identity 🪪
• startup — the startup function of the step, aka what it does when things spin up 🔥
• teardown — the teardown function</teardown> of the step, aka the goodbye routine when things wind down 💀
• cant_stop — a bool that says bringup/teardown can't be stopped at this step 🛑 like, no take-backsies, periodt
• multi_instance — a bool meaning the state has multiple instances which get added afterwards 👑 (yes, plural, she's multifaceted)

💡 quick vibe check: startup and teardown are each a union of a single and a multi function pointer — single takes (unsigned int cpu), multi takes (unsigned int cpu, struct hlist_node *node). iykyk 🧚

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⭐ SEE ALSO ⭐

go bestie, go read these too, they're all icons fr fr:

• Kernel file ./kernel/cpu.c struct cpuhp_cpu_state(9)
• cpuhp_invoke_callback(9)
• cpuhp_ap_update_sync_state(9)
• cpuhp_ap_report_dead(9)
• cpuhp_ap_sync_alive(9)
• clear_tasks_mm_cpumask(9)
• cpu_device_down(9)
• notify_cpu_starting(9)
• cpu_device_up(9)
• bringup_hibernate_cpu(9)
• __cpuhp_setup_state_cpuslocked(9)
• __cpuhp_remove_state_cpuslocked(9)

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and that's the tea 🍓 this lil page lives under ./kernel, dated October 2026, and it's part of the Kernel API Manual — slay, go hotplug some CPUs responsibly 💜✨