__futex_hash(9)

💅 __futex_hash — Kernel API Manual, but make it a group chat 🫶

okay so bestie, welcome to the <pink>Kernel API Manual</pink> ✨ this page is about __futex_hash(9) and honestly it's giving "small function, big feelings" energy. Let's get into it 💖

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🌸 NAME 🌸

__futex_hash — return the hash bucket 🪣✨

like, that's it. that's the whole vibe. it hands you back a hash bucket, no cap.

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🦋 SYNOPSIS 🦋

struct futex_hash_bucket * __futex_hash (union futex_key *key , struct
futex_private_hash *fph , struct futex_private_hash **fph_p );

so you call it like that ⬆️ and it gives you back a struct futex_hash_bucket *. periodt 💅

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🎀 ARGUMENTS 🎀

• key — pointer to the futex key where the hash gets calculated 🔑 like, this is the whole reason we're here, she's the main character.
• fph — pointer to the private hash if you already know it 👀 so if you've got it, pass it in, you're so prepared bestie.
• fph_p — pointer to a private hash pointer, and it's also an output for the private hash used when it's set 📤 so like, it goes in, and info comes back out. multi-tasking icon.

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🔥 DESCRIPTION 🔥

so the way that this works 👑 we hash on the keys returned from get_futex_key (see below, bestie, it's right there) and we return the corresponding hash bucket. simple. elegant. slay.

and here's the lil conditional moment you need to know about 💫

if the FUTEX is PROCESS_PRIVATE, then a per-process hash bucket (from the private hash) is returned if existing. iykyk.

otherwise? a hash bucket from the global hash is returned 🌈 that's the fallback, and she ate.

ngl this is exactly the kind of branch you wanna pay attention to — private hash first, global hash as the otherwise. don't mix 'em up 🙈

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⭐ SEE ALSO ⭐

go read these too, they're all lowkey important 🧚 and they live in this kernel file: ./kernel/futex/core.c

• futex_setup_timer(9)
• get_futex_key(9)
• fault_in_user_writeable(9)
• futex_top_waiter(9)
• wait_for_owner_exiting(9)
• __futex_unqueue(9)
• futex_unqueue(9)
• futex_exit_recursive(9)

fr fr, the whole futex friend group is iconic 💜

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and that's the page!! source/version: ./kernel/futex, dated October 2026 🌸 mwah, go forth and hash responsibly bestie 💅🎀🦋