kref_get_unless_zero(9)

💅 kref_get_unless_zero — a Kernel API Manual moment (section 9, bestie)

okay so bestie, welcome to kref_get_unless_zero(9) from the Kernel API Manual — yes this whole page lives in section 9 and it's iconic. no cap, this one's short but the logic is chef's kiss. 🎀

---

✨ NAME ✨

kref_get_unless_zero — increment the refcount for an object unless it's zero. that's it. that's the whole vibe. 💅

---

✨ SYNOPSIS ✨

int kref_get_unless_zero (struct kref *kref );

---

✨ ARGUMENTS ✨

• kref — the object. that's the whole arg, she's low maintenance. 🦋

---

✨ DESCRIPTION ✨

so here's the tea 🍓: this function exists to make locking around refcounting so much simpler for objects that can be looked up from a lookup structure — and which get removed from that lookup structure inside the object destructor.

operations on objects like that need at least a read lock wrapped around the lookup + kref_get, and a write lock wrapped around kref_put + the removal from the lookup structure. and honestly? RCU implementations get extremely tricky from there. 😭

but here's where it eats 💅✨: if you do a lookup and then a kref_get_unless_zero with return value check, then the locking in the kref_put path can be deferred all the way to the actual removal from the lookup structure — and RCU lookups become trivial. like, embarrassingly easy. main character behaviour, fr fr.

ngl the "with return value check" part is doing a LOT of heavy lifting here — she's bolded and italicised in the original for a reason, bestie. don't skip her. 🙈

---

✨ RETURN ✨

non-zero if the increment succeeded ✨. otherwise, 0. that's it, that's the whole return value arc. 💀

---

✨ SEE ALSO ✨

• the kernel file ./include/linux/kref.h
• kref_init(9)
• kref_get(9)
• kref_put(9)
• kref_put_mutex(9)
• kref_put_lock(9)

go read the whole kref family, they're all baddies. 👑

---

and that's the page, bestie 🫶 — sourced from ./include/linux, dated October 2026, and filed under the kref_get_unless_zero(9) manual. mwah 💋✨