netdev - Re: [net-next PATCH v2 02/15] net: rcu-ify tcf

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Date:	Sun, 24 Aug 2014 22:31:33 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	john.fastabend@...il.com
Cc:	xiyou.wangcong@...il.com, jhs@...atatu.com, eric.dumazet@...il.com,
	netdev@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
	brouer@...hat.com
Subject: Re: [net-next PATCH v2 02/15] net: rcu-ify tcf_proto

From: John Fastabend <john.fastabend@...il.com>
Date: Sun, 24 Aug 2014 17:48:31 -0700

> @@ -722,8 +724,9 @@ static void sfq_free(void *addr)
>  static void sfq_destroy(struct Qdisc *sch)
>  {
>  	struct sfq_sched_data *q = qdisc_priv(sch);
> +	struct tcf_proto *fl = rtnl_dereference(q->filter_list);
>  
> -	tcf_destroy_chain(&q->filter_list);
> +	tcf_destroy_chain(&fl);

This will cause tcf_destroy_chain() to set the local variable
'fl' to NULL rather than q->filter_list.

I don't see how this can be correct at all.

You need to make tcf_destroy_chain() take a pointer to an __rcu
pointer, and do the proper dereferencing and RCU assignments in
that chain destroy loop.

This might be why you're getting annotation warnings.
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