IDR SYNC(9)

✨ idr sync ✨

okay so this is from the Kernel API Manual, section 9, and it's literally called idr sync 💅

🎀 idr synchronization (stolen from radix-tree.h)

bestie, listen. idr_find is able to be called locklessly, using RCU 👑 the caller must ensure calls to this function are made within rcu_read_lock regions. periodt.

other readers (lock-free or otherwise) and modifications may be running concurrently, so like… vibe check your assumptions before you go touching stuff 🙈

🦋 the part where you still have to do your homework

it is still required that the caller manage the synchronization and lifetimes of the items. no cap, that's on you 🫶

so if RCU lock-free lookups are used, typically this would mean that:

• the items have their own locks, or are amenable to lock-free access ✨
• and that the items are freed by RCU (or only freed after having been deleted from the idr tree and a synchronize_rcu grace period) 😭

fr fr do not skip the lifetimes part. the kernel will not be cute about it 💀

🌈 SEE ALSO

• Kernel file ./include/linux/idr.h
• IDR_INIT(9)
• DEFINE_IDR(9)
• idr_get_cursor(9)
• idr_set_cursor(9)
• idr_init_base(9)
• idr_init(9)
• idr_is_empty(9)
• idr_preload_end(9)
• idr_for_each_entry(9)
• idr_for_each_entry_ul(9)
• idr_for_each_entry_continue(9)
• idr_for_each_entry_continue_ul(9)
• ida_alloc(9)
• ida_alloc_min(9)
• ida_alloc_max(9)

💖 and that's the whole page, bestie — so iconic of you to read it. shoutout to ./include/linux for the source, dated October 2026, filed under idr sync(9). slay 🎀🦋✨