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

[Masami Hiramatsu]

On Fri, 28 Aug 2020 10:48:51 +0200
peterz@xxxxxxxxxxxxx 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@xxxxxxxxxx>