rcu_read_lock_bh_held(9)

📦 version 7.3.1, in nixpkgs unstable

💅 rcu_read_lock_bh_held(9) 💅

okay so bestie, welcome to the Kernel API Manual ✨ this one's a lil function from the kernel's RCU corner of the universe and honestly it's giving "are we even in the right place right now?" energy 🫶

🌸 NAME 🌸

rcu_read_lock_bh_held — lowkey asking: might we be in an RCU-bh read-side critical section? 🤔

✨ SYNOPSIS ✨

int notrace rcu_read_lock_bh_held (void );

like, that's the whole vibe. int notrace, takes nothing, returns an int 💖

🎀 ARGUMENTS 🎀

  • void — no arguments, bestie. zero. nada. the function said "I don't need input, I'm the main character" 👑🙈

🦋 DESCRIPTION 🦋

okay so what it actually does: it checks whether bottom half is disabled, and that one check covers both the CONFIG_PROVE_RCU case and the not case 🔥 like, one check, both worlds, slay.

⚠️ heads up though — if someone uses rcu_read_lock_bh, but then later enables BH, then lockdep (if it's enabled) will show the situation. so like, it will snitch. not in a mean way, just in a "lockdep is watching" way 💀

this whole thing is useful for debug checks in functions that require that they be called within an RCU read-side critical section — basically the function gets to be like "am I being called correctly rn or is this a disaster?" 😭✨

it also checks debug_lockdep_rcu_enabled so we don't get false positives during boot — because boot is chaotic enough already, no cap 🙈

🫶 and one more thing: rcu_read_lock_bh is disallowed if the CPU is either idle or offline from an RCU perspective, so this function checks for those as well. fr fr, both of them.

🌈 SEE ALSO 🌈

kernel file ./kernel/rcu/update.c and honestly the whole friend group 💜:

and that's the page!! 💖✨ this lil icon came to you from ./kernel/rcu and the October 2026 release, so like… remember where you got it from, mwah 🎀🦋💅

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