Re: [PATCH net v2] ppp: defer channel free to an RCU grace period to fix pppol2tp RX UAF

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2026-07-08 15:04:32 [+0200], Petr Pavlu wrote:
> As RCU usage in modules is now more common, I see an argument for the
> module loader to invoke rcu_barrier() during module unload to make RCU
> usage easier. In general, module unloading is a rare operation, so even
> if it becomes somewhat slower, I don't expect it to be a significant
> issue.

Okay.

> One problem is that I'm not sure where the new rcu_barrier() call should
> be placed. The prototype adds it before calling the module's exit
> function. Would this actually fit all modules? From a quick look, I can
> see that various modules call it at different points during their exit.

I don't know why you would use call_rcu() in your module_exit()
(pointing to the same module). But you could have call_rcu() invoking
kmem_cache_free() and destroying that cache (kmem_cache_destroy()) in
your exit path. From that perspective it would make sense to flush all
calls before invoking module_exit().

> -- 
> Thanks,
> Petr

Sebastian