linux-kernel - Re: [PATCH 06/14] net: sched: implement reference counted action release

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Message-ID: <20180514164753.GF2134@nanopsycho.orion>
Date:   Mon, 14 May 2018 18:47:53 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Vlad Buslov <vladbu@...lanox.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, jhs@...atatu.com,
        xiyou.wangcong@...il.com, pablo@...filter.org,
        kadlec@...ckhole.kfki.hu, fw@...len.de, ast@...nel.org,
        daniel@...earbox.net, edumazet@...gle.com, keescook@...omium.org,
        linux-kernel@...r.kernel.org, netfilter-devel@...r.kernel.org,
        coreteam@...filter.org, kliteyn@...lanox.com
Subject: Re: [PATCH 06/14] net: sched: implement reference counted action
 release

Mon, May 14, 2018 at 04:27:07PM CEST, vladbu@...lanox.com wrote:

[...]


>+static int tcf_action_del_1(struct net *net, char *kind, u32 index,
>+			    struct netlink_ext_ack *extack)
>+{
>+	const struct tc_action_ops *ops;
>+	int err = -EINVAL;
>+
>+	ops = tc_lookup_action_n(kind);
>+	if (!ops) {

How this can happen? Apparently you hold reference to the module since
you put it couple lines below. In that case, I don't really understand
why you need to lookup and just don't use "ops" pointer you have in
tcf_action_delete().


>+		NL_SET_ERR_MSG(extack, "Specified TC action not found");
>+		goto err_out;
>+	}
>+
>+	if (ops->delete)
>+		err = ops->delete(net, index);
>+
>+	module_put(ops->owner);
>+err_out:
>+	return err;
>+}
>+
> static int tca_action_flush(struct net *net, struct nlattr *nla,
> 			    struct nlmsghdr *n, u32 portid,
> 			    struct netlink_ext_ack *extack)
>@@ -1052,6 +1088,36 @@ static int tca_action_flush(struct net *net, struct nlattr *nla,
> 	return err;
> }
> 
>+static int tcf_action_delete(struct net *net, struct list_head *actions,
>+			     struct netlink_ext_ack *extack)
>+{
>+	int ret;
>+	struct tc_action *a, *tmp;
>+	char kind[IFNAMSIZ];
>+	u32 act_index;
>+
>+	list_for_each_entry_safe(a, tmp, actions, list) {
>+		const struct tc_action_ops *ops = a->ops;
>+
>+		/* Actions can be deleted concurrently
>+		 * so we must save their type and id to search again
>+		 * after reference is released.
>+		 */
>+		strncpy(kind, a->ops->kind, sizeof(kind) - 1);
>+		act_index = a->tcfa_index;
>+
>+		list_del(&a->list);
>+		if (tcf_action_put(a))
>+			module_put(ops->owner);
>+
>+		/* now do the delete */
>+		ret = tcf_action_del_1(net, kind, act_index, extack);
>+		if (ret < 0)
>+			return ret;
>+	}
>+	return 0;
>+}
>+

[...]