wake_up_var_protected(9)

💅 wake_up_var_protected(9)

ok so this is a page from the Kernel API Manual bestie, and it's all about wake_up_var_protected — the little function that wakes up your waiter gorlies while asserting that it's safe to do so. yes ma'am, it checks its own vibes before it wakes anybody. 🫶

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✨ NAME ✨

wake_up_var_protected — wake up waiters for a variable, but like, assert that it is safe first 💅

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✨ SYNOPSIS ✨

wake_up_var_protected (var , cond );

that's it. two args. slay.

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✨ ARGUMENTS ✨

• var — the address of the variable being waited on. like, the actual address, the location, the spot 👀
• cond — the condition which afirms this is safe. (yes the word in the original is "afirms" — we don't touch it, we respect the ancestors 🎀)

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✨ DESCRIPTION ✨

okay so here's the lore. 🌸

When you're waking waiters that use wait_var_event_any_lock, the waker must be holding the relevant lock, otherwise you get races. like, actual races. not the fun kind. 😭

This version of wake_up_var asserts that the relevant lock is held — so no barrier is needed, periodt. it already knows. it checked. it's giving main character energy but in a responsible way.

heads up bestie: the cond is only tested when CONFIG_LOCKDEP is enabled. so if lockdep isn't on, that condition is lowkey just sitting there not being checked. iykyk 🫶

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✨ SEE ALSO ✨

Kernel file ./include/linux/wait_bit.h — and honestly, the whole wait/wake friend group is here, all iconic, all listed, no cap:

• wait_on_bit(9)
• wait_on_bit_io(9)
• wait_on_bit_timeout(9)
• wait_on_bit_action(9)
• wait_on_bit_lock(9)
• wait_on_bit_lock_io(9)
• wait_on_bit_lock_action(9)
• wait_var_event(9)
• wait_var_event_io(9)
• wait_var_event_killable(9)
• wait_var_event_timeout(9)
• wait_var_event_interruptible(9)
• wait_var_event_any_lock(9)
• wait_var_event_spinlock(9)
• wait_var_event_mutex(9)
• wake_up_var_locked(9)
• clear_and_wake_up_bit(9)
• test_and_clear_wake_up_bit(9)
• atomic_dec_and_wake_up(9)
• store_release_wake_up(9)

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okay that's the whole page!! 🦋 this one lives in ./include/linux and it's dated October 2026 — so yeah, future girlie behaviour, we love to see it ✨💖 go wake your variables responsibly, bestie. mwah. 🎀