raw_atomic64_cmpxchg(9)

📦 version 7.3.1, in nixpkgs unstable

💅 raw_atomic64_cmpxchg(9) — from the Kernel API Manual, bestie

okay so picture this: you're deep in the kernel, it's late, and you need a compare-and-swap that goes all the way on the ordering. that's this. welcome to raw_atomic64_cmpxchg(9), the full-ordering baddie of the raw atomic64 family. she's iconic, she's precise, and she has main character energy. 🎀

✨ SYNOPSIS ✨

s64 raw_atomic64_cmpxchg (atomic64_t *v , s64 old , s64 new );

like, that's the whole vibe. three args, one s64 coming back at you. no cap. 🦋

🌸 ARGUMENTS 🌸

  • v — pointer to atomic64_t. this is the thing we're lookin' at, bestie. the target. the moment. 👑
  • old — an s64 value to compare with. like, "is v giving old today or not" energy. 🔍
  • new — an s64 value to assign. this is what v gets to become if the vibe check passes. ✨

💖 DESCRIPTION 💖

okay so here's the tea: if (v == old), it atomically updates v to new with full ordering. like, full. ordering. no shortcuts, no relaxed nonsense, the whole memory-barrier moment. periodt. 🔥

otherwise — and this is the part people miss — v is not modified, and relaxed ordering is provided. so if the compare doesn't hit, you get the chill version. not me having two different orderings in one function 😭

and here's the bonus: it's safe to use in noinstr code. that's literally the whole point of the raw_ prefix, iykyk. but outside of that? please, prefer atomic64_cmpxchg elsewhere. that's not a suggestion, that's the manual telling you directly. 🫶

⭐ RETURN ⭐

the original value of v. that's it, that's the return. 🎁

so yeah, you always find out what was actually in there — whether your compare landed or not — because the function hands you the pre-swap value either way. slay. 💜

🦋 SEE ALSO 🦋

the whole squad, fr fr. every single one of these is (9):

not me listing every single relative and then some 💀 but that's the family, bestie — read them, love them, know them. 🌈

and the kernel file that's living rent-free behind all of this: ./include/linux/atomic/atomic-arch-fallback.h 🐧

okay that's the page!! mwah 💋 this lil slice of lore comes to you from ./include/linux/atomic, dated October 2026 — so yeah, she's from the future and she's still serving full ordering. go forth and compare-and-exchange responsibly, bestie 🫶🎀💖

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