find_alloc_undo(9)

💖 find_alloc_undo(9) 💖

okay bestie, welcome to the Kernel API Manual — this is the page for find_alloc_undo(9), and it’s giving “lookup (and if not present create) undo array” energy ✨

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🌸 NAME 🌸

find_alloc_undo — lookup (and if not present create) undo array

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🎀 SYNOPSIS 🎀

struct sem_undo * find_alloc_undo (struct ipc_namespace *ns , int semid );

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🦋 ARGUMENTS 🦋

• ns — namespace. literally the namespace, bestie 💅
• semid — semaphore array id. the id for the semaphore array 🫶

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✨ DESCRIPTION ✨

okay so here’s the tea: the function looks up (and if not present creates) the undo structure. no cap, that’s the main character move 👑

the size of the undo structure depends on the size of the semaphore array, so the alloc path is not that straightforward. highkey a little tangled, but it’s fine 💀

Lifetime-rules, bestie — listen up: sem_undo is rcu-protected, and on success, the function performs a rcu_read_lock. periodt. that’s the rule 🌈

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🔥 SEE ALSO 🔥

Kernel file ./ipc/sem.c:

• unmerge_queues(9)
• merge_queues(9)
• newary(9)
• wake_const_ops(9)
• do_smart_wakeup_zero(9)
• update_queue(9)
• set_semotime(9)
• do_smart_update(9)

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okay that’s the whole page, bestie — signing off with ./ipc, October 2026, and find_alloc_undo(9) 💅🫶