generic___test_and_set_bit(9)

💅 generic___test_and_set_bit — from the Kernel API Manual, bestie ✨

Okay so picture this: you're deep in the kernel tree, you open up generic___test_and_set_bit from the Kernel API Manual, and you're like "what does this even do" — don't worry, I got you.

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🌸 NAME 🌸

generic___test_and_set_bit — set a bit and return its old value, like a glow-up for one single bit 👑

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✨ SYNOPSIS ✨

bool generic___test_and_set_bit (unsigned long nr , volatile unsigned long *addr );

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🎀 ARGUMENTS 🎀

• nr — the bit you wanna set 🎯 literally just the bit number, that's it
• addr — the address to count from 📍

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🦋 DESCRIPTION 🦋

So here's the tea, and it's kind of a big deal: this operation is non-atomic and it can be reordered 😭 like, it's not out here protecting you.

And the part that lowkey hurts? If two of these race each other, one can appear to succeed but actually fail 💀 yes, fr fr, it lied to your face.

🚨 So you must protect multiple accesses with a lock. Not optional. Not a vibe suggestion. Get the lock, bestie 🔒

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💜 SEE ALSO 💜

• Kernel file ./include/asm-generic/bitops/generic-non-atomic.h 📁
• generic___set_bit(9)
• generic___change_bit(9)
• generic___test_and_clear_bit(9)
• generic_test_bit(9)
• generic_test_bit_acquire(9)
• const_test_bit(9)

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🫶 okay that's the whole page! This one lives at ./include/asm-generic/bitops, dated October 2026, and it's generic___test_and_set_bit(9) — go forth and lock your accesses, mwah 💋🎀