rcu_head_init(9)

💖 rcu_head_init(9) 💖

okay so bestie, welcome to the Kernel API Manual — yes that's the actual manual name, we're in the big leagues now 🎀 this one's a tiny little function but it's load-bearing, so listen up 👑

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✨ NAME ✨

rcu_head_init — the glow-up ritual you do on an rcu_head so that rcu_head_after_call_rcu() can actually tell you what's going on later 💅

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🌸 SYNOPSIS 🌸

void rcu_head_init (struct rcu_head *rhp );

that's it. that's the whole vibe. one pointer, no return, no drama.

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🦋 ARGUMENTS 🦋

• rhp — the struct rcu_head you're initializing. like, the actual structure, hand it over, she needs the setup 🫶

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💜 DESCRIPTION 💜

okay so picture this: you're planning to call rcu_head_after_call_rcu later to test whether a given rcu_head structure has already been passed to call_rcu. cute, love that for you. but here's the thing — you must also invoke this rcu_head_init function on it just after allocating that structure. no skipping, no "I'll do it later", do it right after alloc. periodt 💀

⚠️ and this is the important part, bestie, don't let it slide: calls to this function must not race with calls to call_rcu, rcu_head_after_call_rcu, or callback invocation. like, not even a little. racing is not it. it's giving undefined behaviour and you do not want that energy 😭

so yeah — init it early, init it clean, and don't let anything else touch it while you do 🌈

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🌟 SEE ALSO 🌟

• Kernel file ./include/linux/rcupdate.h — and literally the entire RCU family reunion, all invited:
• same_state_synchronize_rcu(9), cond_resched_tasks_rcu_qs(9), rcu_softirq_qs_periodic(9), RCU_LOCKDEP_WARN(9), lockdep_assert_in_rcu_read_lock(9), lockdep_assert_in_rcu_read_lock_bh(9), lockdep_assert_in_rcu_read_lock_sched(9), lockdep_assert_in_rcu_reader(9), unrcu_pointer(9), RCU_INITIALIZER(9), rcu_assign_pointer(9), rcu_replace_pointer(9), rcu_access_pointer(9), rcu_dereference_check(9), rcu_dereference_bh_check(9), rcu_dereference_sched_check(9), rcu_dereference_all_check(9), rcu_dereference_protected(9), rcu_dereference(9), rcu_dereference_bh(9), rcu_dereference_sched(9), rcu_dereference_all(9), rcu_pointer_handoff(9), rcu_read_lock(9), rcu_read_unlock(9), rcu_read_lock_bh(9), rcu_read_unlock_bh(9), rcu_read_lock_sched(9), rcu_read_unlock_sched(9), RCU_INIT_POINTER(9), RCU_POINTER_INITIALIZER(9), kfree_rcu(9), kfree_rcu_mightsleep(9), kfree_rcu_nolock(9), rcu_head_after_call_rcu(9)

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and that's the whole page, bestie, you ate that 🍓

sign-off time 🧚 this lil gem lives in the source tree at ./include/linux and it's stamped October 2026 — so like, mark your calendar, the rcu_head_init(9) girlies are thriving 💅✨💖