Subject: Re: [Patch net 05/13] cls_cgroup: use tcf_exts_get_net() before call_rcu()

From: Roman Mashak <[email-masked]>
Date: Thu, 09 Nov 2017 17:31:10 -0500

Cong Wang <[email-masked]> writes:

[...]

>  static void cls_cgroup_destroy_work(struct work_struct *work)
>  {
>  	struct cls_cgroup_head *head = container_of(work,
>  						    struct cls_cgroup_head,
>  						    work);
>  	rtnl_lock();
> -	tcf_exts_destroy(&head->exts);
> -	tcf_em_tree_destroy(&head->ematches);
> -	kfree(head);
> +	__cls_cgroup_destroy(head);
>  	rtnl_unlock();
>  }
>  
> @@ -124,8 +130,10 @@ static int cls_cgroup_change(struct net *net, struct sk_buff *in_skb,
>  		goto errout;
>  
>  	rcu_assign_pointer(tp->root, new);
> -	if (head)
> +	if (head) {
> +		tcf_exts_get_net(&head->exts);
>  		call_rcu(&head->rcu, cls_cgroup_destroy_rcu);

In this case why do you not need to care about success/failure of
tcf_exts_get_net() ?

> +	}
>  	return 0;
>  errout:
>  	tcf_exts_destroy(&new->exts);
> @@ -138,8 +146,12 @@ static void cls_cgroup_destroy(struct tcf_proto *tp)
>  	struct cls_cgroup_head *head = rtnl_dereference(tp->root);
>  
>  	/* Head can still be NULL due to cls_cgroup_init(). */
> -	if (head)
> -		call_rcu(&head->rcu, cls_cgroup_destroy_rcu);
> +	if (head) {
> +		if (tcf_exts_get_net(&head->exts))
> +			call_rcu(&head->rcu, cls_cgroup_destroy_rcu);
> +		else
> +			__cls_cgroup_destroy(head);
> +	}
>  }
>  
>  static int cls_cgroup_delete(struct tcf_proto *tp, void *arg, bool *last)