__vdso_fute...4_try_unlock(9)

🦋 NAME 🦋

okay so bestie, __vdso_futex_robust_list64_try_unlock — it tries to unlock an uncontended robust futex with a 64-bit pending op pointer. literally that's the whole vibe ✨

this one lives in the Kernel API Manual, just so u know what corner of the world we're in 🫶

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🌸 SYNOPSIS 🌸

__u32 __vdso_futex_robust_list64_try_unlock (__u32 *lock , __u32 tid ,
__u64 *pop );

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💅 ARGUMENTS 💅

• lock — pointer to the futex lock object 👑
• tid — the TID of the calling task, iykyk
• pop — pointer to the task's robust_list_head::list_pending_op 🎀

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⭐ RETURN ⭐

it hands u back the content of *lock. and on success? that's literally the same as tid. slay 💖

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🔥 DESCRIPTION 🔥

so the function implements this exact thing, no cap:

if (atomic_try_cmpxchg(lock, tid, 0)) *op = NULL; return tid;

now here's the tea ☕ — there's a race between a successful unlock and clearing the pending op pointer in the robust list head. like, they're both happening and it's giving chaos 😭 if the calling task gets interrupted inside that race window and has to handle a (fatal) signal on return to user space, then the kernel handles the clearing of pending_op before attempting to deliver the signal. why? because that ensures a task can't exit with a potentially invalid pending op pointer. protection periodt 🛡️

user space uses it like this, fr fr:

if (__vdso_futex_robust_list64_try_unlock(lock, tid, pending_op) != tid)
err = sys_futex($OP | FUTEX_ROBUST_UNLOCK,....);

and if the unlock attempt fails because the FUTEX_WAITERS bit is set in the lock? then the syscall does the unlock, clears the pending op pointer, and wakes the requested number of waiters. iconic multi-tasking energy 👑

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🧚 SEE ALSO 🧚

• Kernel file ./include/vdso/futex.h
• __vdso_futex_robust_list32_try_unlock(9) — the 32-bit bestie, go say hi 🦋

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and that's the whole page!! sourced from ./include/vdso, dated October 2026 — mwah, drink water, and may ur futexes never stay contended 💜🎀✨