futex_atomi...atomic_local(9)

✨ futex_atomic_cmpxchg_inatomic_local(9) ✨

okay so bestie, welcome to the Kernel API Manual 💖 this one's a kernel-space girly and she's lowkey doing the most important job: the atomic compare-and-exchange for futexes. no cap, she's iconic.

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🌸 NAME 🌸

futex_atomic_cmpxchg_inatomic_local — compares the content of uaddr with newval, and swaps it in only if the current value is oldval. it's giving "i'll only change if you're exactly who i expected you to be" 💅

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🎀 SYNOPSIS 🎀

int futex_atomic_cmpxchg_inatomic_local (u32 *uval , u32 __user *uaddr ,
u32 oldval , u32 newval );

that's the whole vibe. four args, one int back. slay.

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🦋 ARGUMENTS 🦋

okay let's meet the cast 🫶

• uval — pointer to store content of uaddr. she's the little notepad where the result gets written down 📝
• uaddr — pointer to user space address. yes bestie, user space, tread carefully 👀
• oldval — old value. the expected one, the one we're checking against ⭐
• newval — new value to store to uaddr. the glow-up we're trying to apply 💫

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🔥 RETURN 🔥

the return value is literally the whole plot, so pay attention 🙈

• 0 — on success 🎉
• -EFAULT — user access resulted in a page fault 😭
• -EAGAIN — atomic operation was unable to complete due to contention 💀

fr fr, if you see -EAGAIN it's not a you problem, it's just the vibes being contested. try again later ✨

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👑 SEE ALSO 👑

• Kernel file ./include/asm-generic/futex.h — go read the source, iykyk 📖
• futex_atomic_op_inuser_local(9) — her sibling, also doing atomic things 🌈

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and that's the tea 🍓 this page lives in ./include/asm-generic, dated October 2026, and it's brought to you by the futex_atomi...atomic_local(9) girlies themselves. mwah, ily, go write some lock-free code responsibly 💜🧚