ct_idle_enter(9)

💤 ct_idle_enter(9) 💤

okay so this is a page from the Kernel API Manual — yes, the kernel has lore too, and this lil function is lowkey iconic in the context-tracking world 🎀

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✨ NAME ✨

ct_idle_enter — the function that tells RCU "bestie, this CPU is heading into idle mode, don't wait up" 💅

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🌸 SYNOPSIS 🌸

void noinstr ct_idle_enter (void );

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🦋 ARGUMENTS 🦋

• void — literally no arguments. nothing. zero. the void is voiding 🙈

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💖 DESCRIPTION 💖

So what it does: it enters idle mode. Which is to say — and this is the important bit — it -leaves- the mode where RCU read-side critical sections can occur. like, it's the exit door for that whole situation 🚪✨

(and yes, before you come for me: RCU read-side critical sections can still occur in irq handlers while in idle. that whole possibility is handled by irq_enter and irq_exit, so don't @ me 🫶)

⚠️ no cap warning: if you add or remove a call to ct_idle_enter, you gotta test with CONFIG_RCU_EQS_DEBUG=y. like, actually test it. fr fr. don't skip this, it's giving "i'll test in prod" energy and that's not the vibe 💀

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👑 SEE ALSO 👑

• the kernel file ./kernel/context_tracking.c — go read it, it's the main character of this story ⭐
• ct_nmi_exit(9)
• ct_nmi_enter(9)
• ct_idle_exit(9)
• ct_irq_enter(9)
• ct_irq_exit(9)
• __ct_user_enter(9)
• user_enter_callable(9)
• __ct_user_exit(9)
• user_exit_callable(9)

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okay that's the whole page, slay 💅✨ this was ./kernel, October 2026 — catch you on the next one, bestie 🦋🌈💜