atomic_try_cmpxchg_relaxed(9)

📦 version 7.3.1, in nixpkgs unstable

✨ atomic_try_cmpxchg_relaxed ✨

okay so bestie, this is a page from the Kernel API Manual — yes, the Kernel API Manual, we're doing real kernel hours 💅 — and it's all about one lil function called atomic_try_cmpxchg_relaxed. it does a compare-and-exchange on an atomic variable, but ~chill~ about the ordering. let's get into it 🫶

🌸 NAME 🌸

atomic_try_cmpxchg_relaxed — the atomic compare and exchange that's got relaxed ordering vibes ✨

🦋 SYNOPSIS 🦋

bool atomic_try_cmpxchg_relaxed (atomic_t *v , int *old , int new );

like, look at her. returns a bool, takes three things. iconic signature honestly 👑

🎀 ARGUMENTS 🎀

  • v — a pointer to atomic_t. this is the variable we're doing the whole operation on, no big deal 💖
  • old — a pointer to an int value, and it's the thing we compare against. heads up, she's also an out param later, so she's booked and busy 😭
  • new — the int value we're gonna assign. the new kid on the block 🦋

🔥 DESCRIPTION 🔥

okay so here's the tea ☕ — if (v == old), then v gets atomically updated to new with relaxed ordering. slay, done, exchange complete ✨

but if that comparison does not hold? then v is not modified at all (she stays exactly as she was, main character energy 💅), and instead old gets updated to the current value of v. and relaxed ordering is provided either way, so that part's consistent, no cap.

⚠️ important warning bestie, do not skip this: it is unsafe to use in noinstr code! if you're in noinstr land, use raw_atomic_try_cmpxchg_relaxed there instead. i'm literally begging you 🙈

💀 RETURN 💀

  • true — the exchange actually happened 🎉
  • false — it did not, better luck next time 😭

🌈 SEE ALSO 🌈

the whole extended family, fr fr. these all live in the kernel file ./include/linux/atomic/atomic-instrumented.h by the way 🧚

💜 the 32-bit girlies — atomic_*

🦋 the 64-bit icons — atomic64_*

⭐ the long-distance besties — atomic_long_*

and that's the whole page bestie, you ate that 💅✨ go forth and compare-and-exchange responsibly (and remember: not in noinstr code, use raw_atomic_try_cmpxchg_relaxed there, i'm watching 👀).

mwah 🫶 this lil tour came to you from ./include/linux/atomic, dated October 2026, and yes the page is literally called atomic_try_cmpxchg_relaxed(9) — she's booked, she's titled, she's the moment 💖

📦 where this page comes from