xor_unlock_is_negative_byte(9)

🌸 NAME 🌸

It’s xor_unlock_is_negative_byte, bestie — the Kernel API Manual entry with the long name and a very specific little job. In plain terms: XOR a single byte in memory and test if it is negative, for unlock. Yes, that is literally the whole name-vibe. 💅

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✨ SYNOPSIS ✨

bool xor_unlock_is_negative_byte (unsigned long mask , volatile unsigned
long *addr );

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🎀 ARGUMENTS 🎀

• mask — change the bits which are set in this mask.
• addr — the address of the word containing the byte to change.

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🦋 DESCRIPTION 🦋

Okay so this function changes some of bits 0-6 in the word pointed to by addr. It is atomic and gives release barrier semantics — no cap, that part is important. It’s used to optimise some folio operations which are commonly paired with an unlock or end of writeback. Bit 7 is used as PG_waiters to indicate whether anybody is waiting for the unlock. 🫶

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💖 RETURN 💖

It returns whether the top bit of the byte is set. Simple as that, periodt. ✨

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👑 SEE ALSO 👑

• Kernel file: ./include/asm-generic/bitops/instrumented-lock.h
• clear_bit_unlock(9)
• __clear_bit_unlock(9)
• test_and_set_bit_lock(9)

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Cute sign-off time: source/version is ./include/asm-generic/bitops, dated October 2026, and the page is xor_unlock_is_negative_byte(9). Bye bestie, go be iconic with your bits 🫶💖🎀