netdev - Re: [PATCH v2 net 2/2] net sched actions: decrement module refcount earlier

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Date:   Wed, 19 Apr 2017 17:03:12 +0200 (CEST)
From:   Wolfgang Bumiller <w.bumiller@...xmox.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v2 net 2/2] net sched actions: decrement module refcount
 earlier

> On April 19, 2017 at 1:32 PM Jamal Hadi Salim <jhs@...atatu.com> wrote:
> 
> 
> On 17-04-19 04:09 AM, Wolfgang Bumiller wrote:
> 
> This solves one issue, but I am afraid the issue Cong mentioned is a
> possibility still.
> Lets say user did a replace and tried to also replace the cookie
> in that transaction. The init() succeeds but the cookie allocation
> fails. To be correct we'll have to undo the replace i.e something
> like uninit() which will restore back the old values.
> This is very complex and unnecessary.
> 
> My suggestion:
> If we move the cookie allocation before init we can save it and
> only when init succeeds do we attach it to the action, otherwise
> we free it on error path.

Shouldn't the old code have freed an old a->act_cookie as well before
replacing it then? nla_memdup_cookie() starts off by assigning a->act_cookie.

(I've been running this loop for a while now:
# while : ; do tc actions change action ok index 500 cookie $i; let i++; done
and memory usage *seems* to be growing faster with the loop running - still
slow, but visible. (I stopped most but not all background processes in this
VM))

I don't see the growth with the change below (replacing both patches).
(although given the freeing of the old act_cookie pointer I wonder if
this needs additional locking?)

diff --git a/net/sched/act_api.c b/net/sched/act_api.c
index b70aa57319ea..e05b924618a0 100644
--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c
@@ -529,20 +529,20 @@ int tcf_action_dump(struct sk_buff *skb, struct list_head *actions,
 	return err;
 }
 
-static int nla_memdup_cookie(struct tc_action *a, struct nlattr **tb)
+static struct tc_cookie *nla_memdup_cookie(struct nlattr **tb)
 {
-	a->act_cookie = kzalloc(sizeof(*a->act_cookie), GFP_KERNEL);
-	if (!a->act_cookie)
-		return -ENOMEM;
+	struct tc_cookie *c = kzalloc(sizeof(*c), GFP_KERNEL);
+	if (!c)
+		return NULL;
 
-	a->act_cookie->data = nla_memdup(tb[TCA_ACT_COOKIE], GFP_KERNEL);
-	if (!a->act_cookie->data) {
-		kfree(a->act_cookie);
-		return -ENOMEM;
+	c->data = nla_memdup(tb[TCA_ACT_COOKIE], GFP_KERNEL);
+	if (!c->data) {
+		kfree(c);
+		return NULL;
 	}
-	a->act_cookie->len = nla_len(tb[TCA_ACT_COOKIE]);
+	c->len = nla_len(tb[TCA_ACT_COOKIE]);
 
-	return 0;
+	return c;
 }
 
 struct tc_action *tcf_action_init_1(struct net *net, struct nlattr *nla,
@@ -551,6 +551,7 @@ struct tc_action *tcf_action_init_1(struct net *net, struct nlattr *nla,
 {
 	struct tc_action *a;
 	struct tc_action_ops *a_o;
+	struct tc_cookie *cookie = NULL;
 	char act_name[IFNAMSIZ];
 	struct nlattr *tb[TCA_ACT_MAX + 1];
 	struct nlattr *kind;
@@ -566,6 +567,18 @@ struct tc_action *tcf_action_init_1(struct net *net, struct nlattr *nla,
 			goto err_out;
 		if (nla_strlcpy(act_name, kind, IFNAMSIZ) >= IFNAMSIZ)
 			goto err_out;
+		if (tb[TCA_ACT_COOKIE]) {
+			int cklen = nla_len(tb[TCA_ACT_COOKIE]);
+
+			if (cklen > TC_COOKIE_MAX_SIZE)
+				goto err_out;
+
+			cookie = nla_memdup_cookie(tb);
+			if (!cookie) {
+				err = -ENOMEM;
+				goto err_out;
+			}
+		}
 	} else {
 		err = -EINVAL;
 		if (strlcpy(act_name, name, IFNAMSIZ) >= IFNAMSIZ)
@@ -604,20 +617,12 @@ struct tc_action *tcf_action_init_1(struct net *net, struct nlattr *nla,
 	if (err < 0)
 		goto err_mod;
 
-	if (tb[TCA_ACT_COOKIE]) {
-		int cklen = nla_len(tb[TCA_ACT_COOKIE]);
-
-		if (cklen > TC_COOKIE_MAX_SIZE) {
-			err = -EINVAL;
-			tcf_hash_release(a, bind);
-			goto err_mod;
-		}
-
-		if (nla_memdup_cookie(a, tb) < 0) {
-			err = -ENOMEM;
-			tcf_hash_release(a, bind);
-			goto err_mod;
+	if (name == NULL && tb[TCA_ACT_COOKIE]) {
+		if (a->act_cookie) {
+			kfree(a->act_cookie->data);
+			kfree(a->act_cookie);
 		}
+		a->act_cookie = cookie;
 	}
 
 	/* module count goes up only when brand new policy is created
@@ -632,6 +637,10 @@ struct tc_action *tcf_action_init_1(struct net *net, struct nlattr *nla,
 err_mod:
 	module_put(a_o->owner);
 err_out:
+	if (cookie) {
+		kfree(cookie->data);
+		kfree(cookie);
+	}
 	return ERR_PTR(err);
 }