STRUCT SMP_HOTPLUG_THREAD(9)

✨ NAME ✨

struct smp_hotplug_thread — the descriptor for a CPU-hotplug-related thread, straight out of the Kernel API Manual, bestie 💖

Like, it's literally the little info packet that tells the kernel everything it needs to know about a per-CPU thread: where to stash the task pointers, what to run, and what to do when a CPU ghosts you (goes offline) or comes back online. Iconic behavior tbh.

🌸 SYNOPSIS 🌸

struct smp_hotplug_thread {
    struct task_struct              * __percpu *store;
    struct list_head                list;
    int (*thread_should_run)(unsigned int cpu);
    void (*thread_fn)(unsigned int cpu);
    void (*create)(unsigned int cpu);
    void (*setup)(unsigned int cpu);
    void (*cleanup)(unsigned int cpu, bool online);
    void (*park)(unsigned int cpu);
    void (*unpark)(unsigned int cpu);
    bool selfparking;
    const char                      *thread_comm;
};

🎀 Members 🎀

Okay so here's the whole cast of characters, no skips, no cap 👑

• store — pointer to the per-CPU storage for the task pointers. It's giving "where did I put my keys" but for task structs 🔑
• list — the list head for core management. Lowkey just the plumbing that keeps everything organized 🧵
• thread_should_run — the vibe check function: it checks whether the thread should run or not. Heads up though — it gets called with preemption disabled, so no funny business 😤
• thread_fn — the associated thread function. This is the main character, the actual work 💅
• create — optional setup function, called when the thread gets created. Important: it is not called from the thread context, so don't get it twisted 🙈
• setup — optional setup function, called when the thread gets operational for the first time. First-day-of-school energy 🎒
• cleanup — optional cleanup function, called when the thread should stop (i.e. on module exit). Say bye bestie 😭
• park — optional park function, called when the thread is parked (CPU offline). Nap time 🛌
• unpark — optional unpark function, called when the thread is unparked (CPU online). Wakey wakey ✨
• selfparking — a bool; means the thread is not parked by the park function. It handles its own parking, independent queen 👑
• thread_comm — the base name of the thread. That's its government name on the process list 🪪

🦋 SEE ALSO 🦋

Kernel file ./include/linux/smpboot.h — go read it, iykyk 🫶

And that's the whole page bb! Straight from ./include/linux, dated October 2026, and filed under struct smp_hotplug_thread(9). Slay, go write some hotplug threads 💜🔥