spin_is_locked(9)

💅 spin_is_locked(9) — the Kernel API Manual, bestie edition 🎀

Okay so we're in the spin_is_locked(9) manpage today, and yes she's from the Kernel API Manual, and yes she's iconic, let's get into it ✨

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🌸 NAME 🌸

spin_is_locked — check whether a spinlock is locked, that's literally it, that's the whole vibe 💖

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✨ SYNOPSIS ✨

int spin_is_locked (spinlock_t *lock );

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🦋 ARGUMENTS 🦋

• lock — a pointer to the spinlock, bestie. That's the one you're asking about 🫶

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👑 DESCRIPTION 👑

Okay so the first thing you need to know, and I mean really know: this function is NOT required to provide any memory ordering guarantees. Like, none. Zero. Not a single one. Ngl she's just out here existing 😭

So what's she even for? She could be used for debugging purposes — very that — or, when you actually need additional synchronization, she gets accompanied with other constructs (memory barriers, the real ones) that enforce the synchronization. She's the supporting character, not the main character energy 💅

Note that the function only tells you that the spinlock is seen to be locked — not that it is locked on your CPU. Huge distinction. Massive. Do not conflate them 🙈

Further, on CONFIG_SMP=n builds with CONFIG_DEBUG_SPINLOCK=n, the return value is always 0 (see include/linux/spinlock_up.h). So basically in that config she's out here giving nothing 🧚 Therefore you should not rely heavily on the return value. Like, don't build your whole personality on it, fr fr 💀

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⭐ RETURN ⭐

• 1 if lock is locked 💖
• 0 otherwise 🌸

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🌈 SEE ALSO 🌈

Kernel file ./include/linux/spinlock.h

atomic_dec_and_lock(9)

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And that's the page, bestie — sending you off with the source ./include/linux and the date October 2026, mwah, slay, periodt 💅✨🎀