cpumask_test_and_set_cpu(9)

💅 cpumask_test_and_set_cpu — from the Kernel API Manual, bestie 💖

okay so picture this: you're deep in the kernel, you've got a cpumask, and you need to check one cpu AND flip it on, all in one go, with zero race conditions. that's this function. she's the atomic queen. slay. 👑

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✨ NAME ✨

cpumask_test_and_set_cpu — atomically test and set a cpu in a cpumask 🎀

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🌸 SYNOPSIS 🌸

bool cpumask_test_and_set_cpu (int cpu , struct cpumask *cpumask );

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🦋 ARGUMENTS 🦋

• cpu — the cpu number you're checking, and the vibe check on this one is it must be < nr_cpu_ids 💀 (respect the limit, bestie)
• cpumask — the cpumask pointer. that's your bitmap, your little roster of cpus 🫶

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🧚 DESCRIPTION 🧚

literally it's a test_and_set_bit wrapper for cpumasks. that's the whole thing, and honestly? iconic. 💅

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🔥 RETURN 🔥

true if cpu was set in the old bitmap of cpumask — else it returns false. so you're peeking at the state before the set, not after. iykyk. 😌

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👑 SEE ALSO 👑

so many friends, one big family reunion, and every single one of them is here 🎉

• cpumask_pr_args(9)
• the first-girlies: cpumask_first(9), cpumask_first_zero(9), cpumask_first_and(9), cpumask_first_andnot(9), cpumask_first_and_and(9), cpumask_last(9)
• the next-up crew: cpumask_next(9), cpumask_next_zero(9), cpumask_next_and(9), cpumask_next_andnot(9), cpumask_next_and_wrap(9), cpumask_next_wrap(9), cpumask_random(9)
• the loop icons: for_each_cpu(9), for_each_cpu_wrap(9), for_each_cpu_and(9), for_each_cpu_andnot(9), for_each_cpu_or(9), for_each_cpu_from(9)
• the picky ones: cpumask_any_but(9), cpumask_any_and_but(9), cpumask_any_andnot_but(9), cpumask_nth(9), cpumask_nth_and(9), cpumask_nth_and_andnot(9)
• the set/clear squad: cpumask_set_cpu(9), cpumask_clear_cpus(9), cpumask_clear_cpu(9), cpumask_test_cpu(9), cpumask_test_and_clear_cpu(9), cpumask_setall(9), cpumask_clear(9)
• the bitwise besties: cpumask_and(9), cpumask_or(9), cpumask_weighted_or(9), cpumask_xor(9), cpumask_andnot(9), cpumask_equal(9), cpumask_or_equal(9), cpumask_intersects(9), cpumask_subset(9), cpumask_empty(9), cpumask_full(9), cpumask_weight(9), cpumask_weight_and(9), cpumask_weight_andnot(9)
• the glow-up/dupes: cpumask_shift_right(9), cpumask_shift_left(9), cpumask_copy(9)
• the "just give me one": cpumask_any(9), cpumask_any_and(9), cpumask_of(9)
• the text-parsing girlies: cpumask_parse_user(9), cpumask_parselist_user(9), cpumask_parse(9), cpulist_parse(9)
• the sizing & allocation corner: cpumask_size(9), alloc_cpumask_var(9), to_cpumask(9), num_online_cpus(9)
• the printer besties: cpumap_print_bitmask_to_buf(9), cpumap_print_list_to_buf(9)

and if you wanna read the source yourself (main character behavior honestly), it lives in the kernel file ./include/linux/cpumask.h 📖

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ngl the one rule here: cpu has to be < nr_cpu_ids. no cap. don't be out here passing a cpu number that doesn't exist 🙈

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that's the whole page bestie!! brought to you by ./include/linux, dated October 2026, and this little header goes out to cpumask_test_and_set_cpu(9) — atomic, adorable, absolutely ate. periodt. 💜🌸✨