list_entry_lockless(9)

📦 version 7.3.1, in nixpkgs unstable

💖 list_entry_lockless — bestie's guide to grabbing the struct 💖

okay so real talk, we're deep in the kernel API manual (section 9, the "kernel internals" girlies know) and today's main character is list_entry_lockless. it's a macro. it's giving "small but mighty". let's get into it 🎀

✨ SYNOPSIS ✨

list_entry_lockless (ptr , type , member );

no cap, that's the whole call. three args, zero drama. 💅

🌸 ARGUMENTS 🌸

  • ptr — the struct list_head pointer. this is your starting point, the little node you're turning back into its bigger self. 🦋
  • type — the type of the struct this is embedded in. i.e., what you want back out of this whole situation. 👑
  • member — the name of the list_head within the struct. yes, the member. the inner list head that lives inside your bigger struct. she's literally the key that makes the reverse lookup work. 🔑

🔥 DESCRIPTION 🔥

so what does this primitive actually do? it gets the struct for this entry, bestie — you hand it the list_head pointer and it hands you back the containing struct. iconic behavior. 🫶

and the "lockless" part? not just a cute name. this primitive may safely run concurrently with the _rcu list-mutation primitives — think list_add_rcu and friends — so you can be out here traversing while someone else is mutating. slay. ✨

but — and this is the important part, don't skip it — it requires some implicit RCU read-side guarding. the locklessness is not free. you need to already be under some kind of implicit guard, or this is not it. 🙈

two examples the manual gives you:

  1. running within a special exception-time environment where preemption is disabled and where lockdep cannot be invoked. 🧚
  2. when items are added to the list, but never deleted. 🍓

that's it. those are the vibes. no extra reading, that's what the page says. 💜

💀 SEE ALSO 💀

the whole _rcu friend group lives in the kernel file ./include/linux/rculist.h, and honestly they're all linked below, so let's list them all because we do not gatekeep. 🌈

iykyk, the hlist girlies and the list girlies both showed up for this one. 💅

that's the page, bestie!! 🎀 shoutout to whoever maintains ./include/linux (october 2026 edition, mwah 💋) for keeping this list_entry_lockless(9) lore alive and documented. go forth and be lockless responsibly. 🦋✨

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