notify_cpu_starting(9)

💖 notify_cpu_starting(9) 💖

okay so welcome to the Kernel API Manual, bestie 🫶 — today's main character is notify_cpu_starting(9), and she is literally the call that invokes the callbacks on the starting CPU. no cap. ✨

🎀 NAME 🎀

notify_cpu_starting — Invoke the callbacks on the starting CPU. that's the whole vibe. iconic. 💅

🌸 SYNOPSIS 🌸

void notify_cpu_starting (unsigned int cpu );

🦋 ARGUMENTS 🦋

• cpu — the cpu that just started. yep, that's the one. 💖

🔥 DESCRIPTION 🔥

okay so the rule is: it must be called by the arch code on the new cpu, and the timing is not a suggestion — it has to happen before the new cpu enables interrupts and before the "boot" cpu returns from __cpu_up. it's giving "last checkpoint before go-live" 😭. if you're the arch code, this is your moment — do not skip it, because the original says must. periodt. 💀

👑 SEE ALSO 👑

the Kernel file ./kernel/cpu.c is where the lore lives, and the whole entourage is:

• struct cpuhp_cpu_state(9)
• struct cpuhp_step(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)
• cpu_device_up(9)
• bringup_hibernate_cpu(9)
• __cpuhp_setup_state_cpuslocked(9)
• __cpuhp_remove_state_cpuslocked(9)

mwah 💋 signed off from the ./kernel source/version corner, dated October 2026, in the Kernel API Manual — notify_cpu_starting(9), out 🫶✨