Re: [RFC][PATCH 7/7] kprobes: Replace rp->free_instance with freelist

Masami Hiramatsu
2020-08-28T09:13:47Z

On Fri, 28 Aug 2020 10:48:51 +0200
peterz@infradead.org wrote:

> On Thu, Aug 27, 2020 at 06:12:44PM +0200, Peter Zijlstra wrote:
> > struct kretprobe_instance {
> > union {
> > + /*
> > + * Dodgy as heck, this relies on not clobbering freelist::refs.
> > + * llist: only clobbers freelist::next.
> > + * rcu: clobbers both, but only after rp::freelist is gone.
> > + */
> > + struct freelist_node freelist;
> > struct llist_node llist;
> > - struct hlist_node hlist;
> > struct rcu_head rcu;
> > };
>
> Masami, make sure to make this something like:
>
> union {
> struct freelist_node freelist;
> struct rcu_head rcu;
> };
> struct llist_node llist;
>
> for v4, because after some sleep I'm fairly sure what I wrote above was
> broken.
>
> We'll only use RCU once the freelist is gone, so sharing that storage
> should still be okay.

Hmm, would you mean there is a chance that an instance belongs to
both freelist and llist?

Thank you,

--
Masami Hiramatsu <mhiramat@kernel.org>