rcu_read_lock_held(9)

💅 rcu_read_lock_held(9) — a Kernel API Manual moment

okay so we're deep in the kernel manual bestie, welcome to rcu_read_lock_held(9) 🎀 this is the Kernel API Manual and honestly? this little function is doing the most for your debug checks and it deserves its flowers 🌸

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✨ NAME ✨

rcu_read_lock_held — literally "might we be in RCU read-side critical section?" like that's the whole vibe check 💅

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🦋 SYNOPSIS 🦋

int notrace rcu_read_lock_held (void );

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🌸 ARGUMENTS 🌸

• void — no arguments, babe. zero. none. she takes nothing and she gives everything ✨

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💖 DESCRIPTION 💖

okay so here's the tea 🍓: if CONFIG_DEBUG_LOCK_ALLOC is selected, this returns nonzero iff you're in an RCU read-side critical section. iykyk 😌

in the absence of CONFIG_DEBUG_LOCK_ALLOC, this one just assumes we are in an RCU read-side critical section unless it can prove otherwise. she's trusting like that 🫶 this is useful for debug checks in functions that require that they be called within an RCU read-side critical section — basically "hey are you where you're supposed to be" energy 🔥

she also checks debug_lockdep_rcu_enabled to prevent false positives during boot and while lockdep is disabled. thoughtful queen 👑

⚠️ note bestie: rcu_read_lock and the matching rcu_read_unlock must occur in the same context. for example, it is illegal to invoke rcu_read_unlock in process context if the matching rcu_read_lock was invoked from within an irq handler. like... do not do that. that's a no from me 🙈

⚠️ also note: rcu_read_lock is disallowed if the CPU is either idle or offline from an RCU perspective, so check for those as well. main character energy requires a CPU that's actually online, fr fr 💀

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💜 SEE ALSO 💜

Kernel file ./kernel/rcu/update.c

• rcu_read_lock_held_common(9)
• rcu_async_hurry(9)
• rcu_async_relax(9)
• rcu_expedite_gp(9)
• rcu_unexpedite_gp(9)
• rcu_read_lock_bh_held(9)
• wakeme_after_rcu(9)
• init_rcu_head_on_stack(9)
• destroy_rcu_head_on_stack(9)
• get_completed_synchronize_rcu(9)

the whole friend group, iconic lineup honestly 👑🌈

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and that's the page!! 💫 brought to you by ./kernel/rcu, dated October 2026, and signed off with so much love — go forth and check your RCU contexts responsibly bestie 🧚💜