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Date: Wed, 30 Apr 2014 09:39:59 -0700
From: John Fastabend <john.fastabend@...il.com>
To: xiyou.wangcong@...il.com, jhs@...atatu.com
Cc: netdev@...r.kernel.org, davem@...emloft.net, eric.dumazet@...il.com
Subject: [RFC PATCH 12/15] net: sched: make tc_action safe to walk under RCU
This patch makes tc_actions safe to walk from classifiers under RCU.
Notice that each action act() callback defined in each act_*.c
already does its own locking. This is needed even in the current
infrastructure for the case where users add/remove actions via
'tc actions' and reference them via index from the classifiers.
There are a couple interesting pieces here (i.e. need careful review)
In tcf_exts_exec() the call to tcf_action_exec follows a list_empty
check. However although this is occurring under RCU there is no
guarantee that the list is not empty when tcf_action_exec is called.
This patch fixes up return values from tcf_action_exec() so that
packets wont be dropped on the floor when this occurs. Hopefully
its rare and by using RCU we sort of make this assumption.
Second there is a suspect usage of list_splice_init_rcu() in the
tcf_exts_change() routine. Notice how it is used twice in succession
and the second init works on the src tcf_exts. There is probably a
better way to accomplish that.
Signed-off-by: John Fastabend <john.r.fastabend@...el.com>
---
include/net/act_api.h | 1 +
include/net/pkt_cls.h | 12 ++++++++++--
net/sched/act_api.c | 14 +++++++-------
net/sched/cls_api.c | 17 ++++++++++-------
4 files changed, 28 insertions(+), 16 deletions(-)
diff --git a/include/net/act_api.h b/include/net/act_api.h
index 3ee4c92..ddd0c5a 100644
--- a/include/net/act_api.h
+++ b/include/net/act_api.h
@@ -79,6 +79,7 @@ struct tc_action {
__u32 type; /* for backward compat(TCA_OLD_COMPAT) */
__u32 order;
struct list_head list;
+ struct rcu_head rcu;
};
struct tc_action_ops {
diff --git a/include/net/pkt_cls.h b/include/net/pkt_cls.h
index a2441fb..69f0ec5 100644
--- a/include/net/pkt_cls.h
+++ b/include/net/pkt_cls.h
@@ -63,7 +63,7 @@ tcf_unbind_filter(struct tcf_proto *tp, struct tcf_result *r)
struct tcf_exts {
#ifdef CONFIG_NET_CLS_ACT
__u32 type; /* for backward compat(TCA_OLD_COMPAT) */
- struct list_head actions;
+ struct list_head __rcu actions;
#endif
/* Map to export classifier specific extension TLV types to the
* generic extensions API. Unsupported extensions must be set to 0.
@@ -76,7 +76,7 @@ static inline void tcf_exts_init(struct tcf_exts *exts, int action, int police)
{
#ifdef CONFIG_NET_CLS_ACT
exts->type = 0;
- INIT_LIST_HEAD(&exts->actions);
+ INIT_LIST_HEAD_RCU(&exts->actions);
#endif
exts->action = action;
exts->police = police;
@@ -88,6 +88,8 @@ static inline void tcf_exts_init(struct tcf_exts *exts, int action, int police)
*
* Returns 1 if a predicative extension is present, i.e. an extension which
* might cause further actions and thus overrule the regular tcf_result.
+ *
+ * This check is only valid if done under RTNL.
*/
static inline int
tcf_exts_is_predicative(struct tcf_exts *exts)
@@ -128,6 +130,12 @@ tcf_exts_exec(struct sk_buff *skb, struct tcf_exts *exts,
struct tcf_result *res)
{
#ifdef CONFIG_NET_CLS_ACT
+ /* This check is racy but this is OK, if the list is emptied
+ * before walking the chain of actions the return value has
+ * been updated to return zero. This way packets will not be
+ * dropped when action list deletion occurs after the empty
+ * check but before execution
+ */
if (!list_empty(&exts->actions))
return tcf_action_exec(skb, &exts->actions, res);
#endif
diff --git a/net/sched/act_api.c b/net/sched/act_api.c
index 8a5ba5a..d73a546 100644
--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c
@@ -381,14 +381,14 @@ int tcf_action_exec(struct sk_buff *skb, const struct list_head *actions,
struct tcf_result *res)
{
const struct tc_action *a;
- int ret = -1;
+ int ret = 0;
if (skb->tc_verd & TC_NCLS) {
skb->tc_verd = CLR_TC_NCLS(skb->tc_verd);
ret = TC_ACT_OK;
goto exec_done;
}
- list_for_each_entry(a, actions, list) {
+ list_for_each_entry_rcu(a, actions, list) {
repeat:
ret = a->ops->act(skb, a, res);
if (TC_MUNGED & skb->tc_verd) {
@@ -417,8 +417,8 @@ int tcf_action_destroy(struct list_head *actions, int bind)
module_put(a->ops->owner);
else if (ret < 0)
return ret;
- list_del(&a->list);
- kfree(a);
+ list_del_rcu(&a->list);
+ kfree_rcu(a, rcu);
}
return ret;
}
@@ -584,7 +584,7 @@ int tcf_action_init(struct net *net, struct nlattr *nla,
goto err;
}
act->order = i;
- list_add_tail(&act->list, actions);
+ list_add_tail_rcu(&act->list, actions);
}
return 0;
@@ -746,8 +746,8 @@ static void cleanup_a(struct list_head *actions)
struct tc_action *a, *tmp;
list_for_each_entry_safe(a, tmp, actions, list) {
- list_del(&a->list);
- kfree(a);
+ list_del_rcu(&a->list);
+ kfree_rcu(a, rcu);
}
}
diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index 94c7d38..813e5ca 100644
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -498,7 +498,7 @@ void tcf_exts_destroy(struct tcf_proto *tp, struct tcf_exts *exts)
{
#ifdef CONFIG_NET_CLS_ACT
tcf_action_destroy(&exts->actions, TCA_ACT_UNBIND);
- INIT_LIST_HEAD(&exts->actions);
+ INIT_LIST_HEAD_RCU(&exts->actions);
#endif
}
EXPORT_SYMBOL(tcf_exts_destroy);
@@ -510,7 +510,7 @@ int tcf_exts_validate(struct net *net, struct tcf_proto *tp, struct nlattr **tb,
{
struct tc_action *act;
- INIT_LIST_HEAD(&exts->actions);
+ INIT_LIST_HEAD_RCU(&exts->actions);
if (exts->police && tb[exts->police]) {
act = tcf_action_init_1(net, tb[exts->police], rate_tlv,
"police", TCA_ACT_NOREPLACE,
@@ -519,7 +519,7 @@ int tcf_exts_validate(struct net *net, struct tcf_proto *tp, struct nlattr **tb,
return PTR_ERR(act);
act->type = exts->type = TCA_OLD_COMPAT;
- list_add(&act->list, &exts->actions);
+ list_add_rcu(&act->list, &exts->actions);
} else if (exts->action && tb[exts->action]) {
int err;
err = tcf_action_init(net, tb[exts->action], rate_tlv,
@@ -539,16 +539,19 @@ int tcf_exts_validate(struct net *net, struct tcf_proto *tp, struct nlattr **tb,
}
EXPORT_SYMBOL(tcf_exts_validate);
+/* It is not safe to use src->actions after this due to _init_rcu usage
+ * INIT_LIST_HEAD_RCU() is called on src->actions
+ */
void tcf_exts_change(struct tcf_proto *tp, struct tcf_exts *dst,
struct tcf_exts *src)
{
#ifdef CONFIG_NET_CLS_ACT
if (!list_empty(&src->actions)) {
LIST_HEAD(tmp);
- tcf_tree_lock(tp);
- list_splice_init(&dst->actions, &tmp);
- list_splice(&src->actions, &dst->actions);
- tcf_tree_unlock(tp);
+ list_splice_init_rcu(&dst->actions, &tmp, synchronize_rcu);
+ list_splice_init_rcu(&src->actions,
+ &dst->actions,
+ synchronize_rcu);
tcf_action_destroy(&tmp, TCA_ACT_UNBIND);
}
#endif
--
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