preempt_disable_nested(9)

💅 preempt_disable_nested(9) 💅

okay bestie, buckle up, this one's from the Kernel API Manual and it's honestly kinda iconic once you get what it's doing 🎀

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✨ NAME ✨

preempt_disable_nested — disables preemption inside a section that's already normally preempt-disabled. yes, nested. yes, that's the whole point. slay 🌸

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🦋 SYNOPSIS 🦋

preempt_disable_nested

that's it. no arguments, no drama, just vibes ✨

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💖 DESCRIPTION 💖

so here's the tea ☕ — you use this for code that needs preemption protection inside a critical section that's already implicitly preemption-disabled on kernels that are not PREEMPT_RT enabled. and how does that happen, you ask? by, like, things such as:

• holding a spinlock/rwlock 🔒
• soft interrupt context ⚡
• regular interrupt handlers 🛎️

now on PREEMPT_RT enabled kernels, things are different, and this is the part where it gets spicy 🌶️ — spinlock/rwlock held sections, soft interrupt context, and regular interrupt handlers are preemptible and only prevent migration. so preempt_disable_nested steps in and makes sure preemption is actually disabled for the cases that need CPU local serialization, even on PREEMPT_RT. and for non-PREEMPT_RT kernels? it's literally a NOP. no cap, it just sits there looking pretty 💀

the use cases are code sequences that are not serialized by a particular lock instance, like:

• seqcount write side critical sections where the seqcount isn't associated to a particular lock and therefore the automatic protection mechanism doesn't work 🚫. this is what prevents a live lock against a preempting high priority reader. very main character energy of it, honestly 👑
• RMW per CPU variable updates like vmstat 📊

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🌈 SEE ALSO 🌈

• Kernel file ./include/linux/preempt.h 🗂️
• interrupt_context_level(9)
• preempt_enable_nested(9) — the lil sibling that undoes the vibe 🫶

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bestie reminder: this only exists so CPU local serialization actually holds up on PREEMPT_RT. don't go thinking it does anything extra on the non-PREEMPT_RT side — it's a NOP there, periodt 💅

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and that's the whole page, mwah 💋 — this cutie lives in ./include/linux, it's dated October 2026, and it's brought to you by the preempt_disable_nested(9) era of the kernel docs. go forth and nest your preempt disables responsibly, ily 🧚💜