linux-kernel - Re: [RFC][PATCH 7/7] kprobes: Replace rp->free

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Date:   Fri, 28 Aug 2020 10:48:51 +0200
From:   peterz@...radead.org
To:     linux-kernel@...r.kernel.org, mhiramat@...nel.org
Cc:     Eddy_Wu@...ndmicro.com, x86@...nel.org, davem@...emloft.net,
        rostedt@...dmis.org, naveen.n.rao@...ux.ibm.com,
        anil.s.keshavamurthy@...el.com, linux-arch@...r.kernel.org,
        cameron@...dycamel.com, oleg@...hat.com, will@...nel.org,
        paulmck@...nel.org
Subject: Re: [RFC][PATCH 7/7] kprobes: Replace rp->free_instance with freelist

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.