raw_atomic_fetch_add_unless(9)

okay so bestie, we’re in the Kernel API Manual and today’s main character is raw_atomic_fetch_add_unless(9) — the “atomic add unless value with full ordering” girlie. No cap, she’s lowkey iconic in kernel-land. 💅✨

💖 NAME 💖

raw_atomic_fetch_add_unless — atomic add unless value with full ordering. That’s the whole serve: it’s an atomic add, but it only adds unless a value matches, and it comes with full ordering. Periodt. 🌈

✨ SYNOPSIS ✨

Here’s the exact signature, bestie — copy it character for character:

int raw_atomic_fetch_add_unless (atomic_t *v , int a , int u );

🎀 ARGUMENTS 🎀

These are the three little parameters you’re working with:

• v — pointer to atomic_t. It’s the atomic thing being updated. 🫶
• a — int value to add. ➕
• u — int value to compare with. 👀

🦋 DESCRIPTION 🦋

Okay so here’s the behavior, and it’s actually pretty straightforward once you clock it:

• When (v != u), it atomically updates v to (v + a) with full ordering. Slay.
• Otherwise, v is not modified, and relaxed ordering is provided. So it backs off but still gives you ordering vibes.

Also important: it’s safe to use in noinstr code. But the manual says prefer atomic_fetch_add_unless elsewhere — so don’t just use this one everywhere, okay? 💖

🌸 RETURN 🌸

It returns the original value of v — that’s the receipt, bestie. 🧾💖

🌈 SEE ALSO 🌈

Kernel file: ./include/linux/atomic/atomic-arch-fallback.h

Then the whole extended atomic family is here — every single one, no skips:

raw_atomic_read(9), raw_atomic_read_acquire(9), raw_atomic_set(9),
raw_atomic_set_release(9), raw_atomic_add(9), raw_atomic_add_return(9),
raw_atomic_add_return_acquire(9), raw_atomic_add_return_release(9),
raw_atomic_add_return_relaxed(9), raw_atomic_fetch_add(9),
raw_atomic_fetch_add_acquire(9), raw_atomic_fetch_add_release(9),
raw_atomic_fetch_add_relaxed(9), raw_atomic_sub(9),
raw_atomic_sub_return(9), raw_atomic_sub_return_acquire(9),
raw_atomic_sub_return_release(9), raw_atomic_sub_return_relaxed(9),
raw_atomic_fetch_sub(9), raw_atomic_fetch_sub_acquire(9),
raw_atomic_fetch_sub_release(9), raw_atomic_fetch_sub_relaxed(9),
raw_atomic_inc(9), raw_atomic_inc_return(9),
raw_atomic_inc_return_acquire(9), raw_atomic_inc_return_release(9),
raw_atomic_inc_return_relaxed(9), raw_atomic_fetch_inc(9),
raw_atomic_fetch_inc_acquire(9), raw_atomic_fetch_inc_release(9),
raw_atomic_fetch_inc_relaxed(9), raw_atomic_dec(9),
raw_atomic_dec_return(9), raw_atomic_dec_return_acquire(9),
raw_atomic_dec_return_release(9), raw_atomic_dec_return_relaxed(9),
raw_atomic_fetch_dec(9), raw_atomic_fetch_dec_acquire(9),
raw_atomic_fetch_dec_release(9), raw_atomic_fetch_dec_relaxed(9),
raw_atomic_and(9), raw_atomic_fetch_and(9),
raw_atomic_fetch_and_acquire(9), raw_atomic_fetch_and_release(9),
raw_atomic_fetch_and_relaxed(9), raw_atomic_andnot(9),
raw_atomic_fetch_andnot(9), raw_atomic_fetch_andnot_acquire(9),
raw_atomic_fetch_andnot_release(9), raw_atomic_fetch_andnot_relaxed(9),
raw_atomic_or(9), raw_atomic_fetch_or(9),
raw_atomic_fetch_or_acquire(9), raw_atomic_fetch_or_release(9),
raw_atomic_fetch_or_relaxed(9), raw_atomic_xor(9),
raw_atomic_fetch_xor(9), raw_atomic_fetch_xor_acquire(9),
raw_atomic_fetch_xor_release(9), raw_atomic_fetch_xor_relaxed(9),
raw_atomic_xchg(9), raw_atomic_xchg_acquire(9),
raw_atomic_xchg_release(9), raw_atomic_xchg_relaxed(9),
raw_atomic_cmpxchg(9), raw_atomic_cmpxchg_acquire(9),
raw_atomic_cmpxchg_release(9), raw_atomic_cmpxchg_relaxed(9),
raw_atomic_try_cmpxchg(9), raw_atomic_try_cmpxchg_acquire(9),
raw_atomic_try_cmpxchg_release(9), raw_atomic_try_cmpxchg_relaxed(9),
raw_atomic_sub_and_test(9), raw_atomic_dec_and_test(9),
raw_atomic_inc_and_test(9), raw_atomic_add_negative(9),
raw_atomic_add_negative_acquire(9), raw_atomic_add_negative_release(9),
raw_atomic_add_negative_relaxed(9), raw_atomic_add_unless(9),
raw_atomic_inc_not_zero(9), raw_atomic_inc_unless_negative(9),
raw_atomic_dec_unless_positive(9), raw_atomic_dec_if_positive(9),
raw_atomic64_read(9), raw_atomic64_read_acquire(9), raw_atomic64_set(9),
raw_atomic64_set_release(9), raw_atomic64_add(9),
raw_atomic64_add_return(9), raw_atomic64_add_return_acquire(9),
raw_atomic64_add_return_release(9), raw_atomic64_add_return_relaxed(9),
raw_atomic64_fetch_add(9), raw_atomic64_fetch_add_acquire(9),
raw_atomic64_fetch_add_release(9), raw_atomic64_fetch_add_relaxed(9),
raw_atomic64_sub(9), raw_atomic64_sub_return(9),
raw_atomic64_sub_return_acquire(9), raw_atomic64_sub_return_release(9),
raw_atomic64_sub_return_relaxed(9), raw_atomic64_fetch_sub(9),
raw_atomic64_fetch_sub_acquire(9), raw_atomic64_fetch_sub_release(9),
raw_atomic64_fetch_sub_relaxed(9), raw_atomic64_inc(9),
raw_atomic64_inc_return(9), raw_atomic64_inc_return_acquire(9),
raw_atomic64_inc_return_release(9), raw_atomic64_inc_return_relaxed(9),
raw_atomic64_fetch_inc(9), raw_atomic64_fetch_inc_acquire(9),
raw_atomic64_fetch_inc_release(9), raw_atomic64_fetch_inc_relaxed(9),
raw_atomic64_dec(9), raw_atomic64_dec_return(9),
raw_atomic64_dec_return_acquire(9), raw_atomic64_dec_return_release(9),
raw_atomic64_dec_return_relaxed(9), raw_atomic64_fetch_dec(9),
raw_atomic64_fetch_dec_acquire(9), raw_atomic64_fetch_dec_release(9),
raw_atomic64_fetch_dec_relaxed(9), raw_atomic64_and(9),
raw_atomic64_fetch_and(9), raw_atomic64_fetch_and_acquire(9),
raw_atomic64_fetch_and_release(9), raw_atomic64_fetch_and_relaxed(9),
raw_atomic64_andnot(9), raw_atomic64_fetch_andnot(9),
raw_atomic64_fetch_andnot_acquire(9),
raw_atomic64_fetch_andnot_release(9),
raw_atomic64_fetch_andnot_relaxed(9), raw_atomic64_or(9),
raw_atomic64_fetch_or(9), raw_atomic64_fetch_or_acquire(9),
raw_atomic64_fetch_or_release(9), raw_atomic64_fetch_or_relaxed(9),
raw_atomic64_xor(9), raw_atomic64_fetch_xor(9),
raw_atomic64_fetch_xor_acquire(9), raw_atomic64_fetch_xor_release(9),
raw_atomic64_fetch_xor_relaxed(9), raw_atomic64_xchg(9),
raw_atomic64_xchg_acquire(9), raw_atomic64_xchg_release(9),
raw_atomic64_xchg_relaxed(9), raw_atomic64_cmpxchg(9),
raw_atomic64_cmpxchg_acquire(9), raw_atomic64_cmpxchg_release(9),
raw_atomic64_cmpxchg_relaxed(9), raw_atomic64_try_cmpxchg(9),
raw_atomic64_try_cmpxchg_acquire(9),
raw_atomic64_try_cmpxchg_release(9),
raw_atomic64_try_cmpxchg_relaxed(9), raw_atomic64_sub_and_test(9),
raw_atomic64_dec_and_test(9), raw_atomic64_inc_and_test(9),
raw_atomic64_add_negative(9), raw_atomic64_add_negative_acquire(9),
raw_atomic64_add_negative_release(9),
raw_atomic64_add_negative_relaxed(9), raw_atomic64_fetch_add_unless(9),
raw_atomic64_add_unless(9), raw_atomic64_inc_not_zero(9),
raw_atomic64_inc_unless_negative(9),
raw_atomic64_dec_unless_positive(9), raw_atomic64_dec_if_positive(9)

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💖 cute sign-off: source/version ./include/linux/atomic, date October 2026, for raw_atomic_fetch_add_unless(9) — mwah, bye bestie! 🎀✨