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Why Are RCU Leaks Special?

This same pointer-leak problem exists with locking, so it is only fair to ask why we should worry so much about RCU pointer leaks. One answer is that RCU's grace-period delays make it much harder for tools such as KASAN to catch pointer leaks.

What on Earth Does Pointer Provenance Have to do With RCU?

August 6, 2025 from paulmck TL;DR: Unless you are doing very strange things with RCU (read-copy update), not much!!!

What is Pointer Provenance?

Back in the old days, provenance was for objets d'art and the like, and we did not need them for our pointers, no sirree!!! Pointers had bits, those bits formed memory addresses, and as often as not we didn't even need to worry about these addresses being translated. But life is more complicated now.

Why Would Anyone Use Invalid/Dangling Pointers?

Please allow me to introduce you to the famous and frequently re-invented LIFO Push algorithm. You can find this in many places, but let's focus on the Linux kernel's llist_add_batch() and llist_del_all() functions.

What Are Unreasonable Fixes?

We can protect pointers from invalidity by storing them as integers, but: Suppose someone has an element that they are passing to a library function. They should not be required to convert all their ->next pointers to integer just because the library's developers decide to switch to the LIFO Push algorithm for some obscure internal operation.