task_call_func(9)

💅 task_call_func — like, the Kernel API Manual, section 9, bestie

okay so real talk: this is task_call_func(9) from the Kernel API Manual (yes, section 9, the ~spicy~ section) and it's genuinely one of the most "let me just freeze time for a sec" functions in the scheduler. iykyk. 🧚

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✨ NAME ✨

task_call_func — invoke a function on a task in a fixed state 🎀

like... you pin the task down, you call your little function on it, and the state literally cannot move. slay.

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🌸 SYNOPSIS 🌸

int task_call_func (struct task_struct *p , task_call_f func , void *arg
);

(the weird line break is not a typo, that's just how the manpage wrote it, don't come for me 💀 — it's all one call fr fr)

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🦋 ARGUMENTS 🦋

• p — the process you want the function invoked on. and yes bestie, it can be current. main character energy, honestly 👑
• func — the function you're invoking. this is your moment, your callback, your time to shine ✨
• arg — the argument you're handing to func. it's giving "here, hold this" 🫶

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💖 DESCRIPTION 💖

so the whole vibe here: task_call_func fixes the task in its current state by avoiding wakeups and/or rq operations, and then calls func(arg) on it. that's it. that's the whole thing. periodt. 💅

and like — this function can use task_is_runnable and task_curr to work out what the state actually is, if you need that. handy, right? 😌

⚠️ okay but listen: given that func can be invoked with a runqueue lock held, it had better be quite lightweight. like. quite lightweight. no cap. if your callback is doing a whole side quest in there, that's on you and it's not gonna be iconic, it's gonna be a problem 😭🔥

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⭐ RETURN ⭐

whatever func returns. that's it. you get back what your baby function gives back 🎀 (no extra wrapping, no surprises, we're not like that)

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🌈 SEE ALSO 🌈

kernel file ./kernel/sched/core.c — go read it, it's right there:

• wake_q_add(9)
• wake_q_add_safe(9)
• task_curr(9)
• try_to_wake_up(9)
• cpu_curr_snapshot(9)
• wake_up_process(9)
• preempt_notifier_register(9)
• preempt_notifier_unregister(9)
• prepare_task_switch(9)
• finish_task_switch(9)
• schedule_tail(9)
• schedule_preempt_disabled(9)
• preempt_schedule_notrace(9)
• init_idle(9)
• curr_task(9)

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anyway that's the page!! 💜 it lives in ./kernel/sched, it's dated October 2026, and it came to you straight from the Kernel API Manual task_call_func(9). go be lightweight with your callbacks and stay hydrated, bestie 🍓🦋✨