sync_test_and_change_bit(9)

okay so bestie, this is the sync_test_and_change_bit(9) page from the Kernel API Manual, and it's giving “change a bit, return the old value” main character energy 💅✨

🌸 NAME 🌸

sync_test_and_change_bit — change a bit and return its old value. Periodt. 💖

✨ SYNOPSIS ✨

int sync_test_and_change_bit (long nr , volatile unsigned long *addr );

🎀 ARGUMENTS 🎀

• nr — the bit to change, bestie.
• addr — the address to count from. Yes, that’s the wording fr fr.

💅 DESCRIPTION 💅

okay so the actual tea: this operation is atomic and cannot be reordered. It also implies a memory barrier. That’s the whole lore — no cap. 🦋

👑 SEE ALSO 👑

Kernel file ./arch/x86/include/asm/sync_bitops.h is the home base, and these are the other icons you’re gonna want to check:

• sync_set_bit(9)
• sync_clear_bit(9)
• sync_change_bit(9)
• sync_test_and_set_bit(9)
• sync_test_and_clear_bit(9)

kisses and bit-flips, bestie 🫶 — this page’s source/version is ./arch/x86/include/asm, dated October 2026, signing off as sync_test_and_change_bit(9) 💖