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Message-ID: <20140920045031.9869.76112.stgit@nitbit.x32>
Date: Fri, 19 Sep 2014 21:50:34 -0700
From: John Fastabend <john.fastabend@...il.com>
To: xiyou.wangcong@...il.com, jhs@...atatu.com, eric.dumazet@...il.com,
davem@...emloft.net
Cc: netdev@...r.kernel.org
Subject: [net-next PATCH v2 2/2] net: sched: cls_u32 changes to knode must
appear atomic to readers
Changes to the cls_u32 classifier must appear atomic to the
readers. Before this patch if a change is requested for both
the exts and ifindex, first the ifindex is updated then the
exts with tcf_exts_change(). This opens a small window where
a reader can have a exts chain with an incorrect ifindex. This
violates the the RCU semantics.
Here we resolve this by always passing u32_set_parms() a copy
of the tc_u_knode to work on and then inserting it into the hash
table after the updates have been successfully applied.
Tested with the following short script:
#tc filter add dev p3p2 parent 8001:0 protocol ip prio 99 handle 1: \
u32 divisor 256
#tc filter add dev p3p2 parent 8001:0 protocol ip prio 99 \
u32 link 1: hashkey mask ffffff00 at 12 \
match ip src 192.168.8.0/2
#tc filter add dev p3p2 parent 8001:0 protocol ip prio 102 \
handle 1::10 u32 classid 1:2 ht 1: \
match ip src 192.168.8.0/8 match ip tos 0x0a 1e
#tc filter change dev p3p2 parent 8001:0 protocol ip prio 102 \
handle 1::10 u32 classid 1:2 ht 1: \
match ip src 1.1.0.0/8 match ip tos 0x0b 1e
CC: Eric Dumazet <edumazet@...gle.com>
CC: Jamal Hadi Salim <jhs@...atatu.com>
Signed-off-by: John Fastabend <john.r.fastabend@...el.com>
---
net/sched/cls_u32.c | 135 ++++++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 126 insertions(+), 9 deletions(-)
diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index 8d90e50..e3fb530 100644
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -354,27 +354,53 @@ static int u32_init(struct tcf_proto *tp)
return 0;
}
-static int u32_destroy_key(struct tcf_proto *tp, struct tc_u_knode *n)
+static int u32_destroy_key(struct tcf_proto *tp,
+ struct tc_u_knode *n,
+ bool free_pf)
{
tcf_unbind_filter(tp, &n->res);
tcf_exts_destroy(tp, &n->exts);
if (n->ht_down)
n->ht_down->refcnt--;
#ifdef CONFIG_CLS_U32_PERF
- free_percpu(n->pf);
+ if (free_pf)
+ free_percpu(n->pf);
#endif
#ifdef CONFIG_CLS_U32_MARK
- free_percpu(n->pcpu_success);
+ if (free_pf)
+ free_percpu(n->pcpu_success);
#endif
kfree(n);
return 0;
}
+/* u32_delete_key_rcu should be called when free'ing a copied
+ * version of a tc_u_knode obtained from u32_init_knode(). When
+ * copies are obtained from u32_init_knode() the statistics are
+ * shared between the old and new copies to allow readers to
+ * continue to update the statistics during the copy. To support
+ * this the u32_delete_key_rcu variant does not free the percpu
+ * statistics.
+ */
static void u32_delete_key_rcu(struct rcu_head *rcu)
{
struct tc_u_knode *key = container_of(rcu, struct tc_u_knode, rcu);
- u32_destroy_key(key->tp, key);
+ u32_destroy_key(key->tp, key, false);
+}
+
+/* u32_delete_key_freepf_rcu is the rcu callback variant
+ * that free's the entire structure including the statistics
+ * percpu variables. Only use this if the key is not a copy
+ * returned by u32_init_knode(). See u32_delete_key_rcu()
+ * for the variant that should be used with keys return from
+ * u32_init_knode()
+ */
+static void u32_delete_key_freepf_rcu(struct rcu_head *rcu)
+{
+ struct tc_u_knode *key = container_of(rcu, struct tc_u_knode, rcu);
+
+ u32_destroy_key(key->tp, key, true);
}
static int u32_delete_key(struct tcf_proto *tp, struct tc_u_knode *key)
@@ -390,7 +416,7 @@ static int u32_delete_key(struct tcf_proto *tp, struct tc_u_knode *key)
if (pkp == key) {
RCU_INIT_POINTER(*kp, key->next);
- call_rcu(&key->rcu, u32_delete_key_rcu);
+ call_rcu(&key->rcu, u32_delete_key_freepf_rcu);
return 0;
}
}
@@ -408,7 +434,7 @@ static void u32_clear_hnode(struct tc_u_hnode *ht)
while ((n = rtnl_dereference(ht->ht[h])) != NULL) {
RCU_INIT_POINTER(ht->ht[h],
rtnl_dereference(n->next));
- call_rcu(&n->rcu, u32_delete_key_rcu);
+ call_rcu(&n->rcu, u32_delete_key_freepf_rcu);
}
}
}
@@ -584,6 +610,82 @@ errout:
return err;
}
+static void u32_replace_knode(struct tcf_proto *tp,
+ struct tc_u_common *tp_c,
+ struct tc_u_knode *n)
+{
+ struct tc_u_knode __rcu **ins;
+ struct tc_u_knode *pins;
+ struct tc_u_hnode *ht;
+
+ if (TC_U32_HTID(n->handle) == TC_U32_ROOT)
+ ht = rtnl_dereference(tp->root);
+ else
+ ht = u32_lookup_ht(tp_c, TC_U32_HTID(n->handle));
+
+ ins = &ht->ht[TC_U32_HASH(n->handle)];
+
+ /* The node must always exist for it to be replaced if this is not the
+ * case then something went very wrong elsewhere.
+ */
+ for (pins = rtnl_dereference(*ins); ;
+ ins = &pins->next, pins = rtnl_dereference(*ins))
+ if (pins->handle == n->handle)
+ break;
+
+ RCU_INIT_POINTER(n->next, pins->next);
+ rcu_assign_pointer(*ins, n);
+}
+
+static struct tc_u_knode *u32_init_knode(struct tcf_proto *tp,
+ struct tc_u_knode *n)
+{
+ struct tc_u_knode *new;
+ struct tc_u32_sel *s = &n->sel;
+
+ new = kzalloc(sizeof(*n) + s->nkeys*sizeof(struct tc_u32_key),
+ GFP_KERNEL);
+
+ if (!new)
+ return NULL;
+
+ RCU_INIT_POINTER(new->next, n->next);
+ new->handle = n->handle;
+ RCU_INIT_POINTER(new->ht_up, n->ht_up);
+
+#ifdef CONFIG_NET_CLS_IND
+ new->ifindex = n->ifindex;
+#endif
+ new->fshift = n->fshift;
+ new->res = n->res;
+ RCU_INIT_POINTER(new->ht_down, n->ht_down);
+
+ /* bump reference count as long as we hold pointer to structure */
+ if (new->ht_down)
+ new->ht_down->refcnt++;
+
+#ifdef CONFIG_CLS_U32_PERF
+ /* Statistics may be incremented by readers during update
+ * so we must keep them in tact. When the node is later destroyed
+ * a special destroy call must be made to not free the pf memory.
+ */
+ new->pf = n->pf;
+#endif
+
+#ifdef CONFIG_CLS_U32_MARK
+ new->val = n->val;
+ new->mask = n->mask;
+ /* Similarly success statistics must be moved as pointers */
+ new->pcpu_success = n->pcpu_success;
+#endif
+ new->tp = tp;
+ memcpy(&new->sel, s, sizeof(*s) + s->nkeys*sizeof(struct tc_u32_key));
+
+ tcf_exts_init(&new->exts, TCA_U32_ACT, TCA_U32_POLICE);
+
+ return new;
+}
+
static int u32_change(struct net *net, struct sk_buff *in_skb,
struct tcf_proto *tp, unsigned long base, u32 handle,
struct nlattr **tca,
@@ -610,12 +712,27 @@ static int u32_change(struct net *net, struct sk_buff *in_skb,
n = (struct tc_u_knode *)*arg;
if (n) {
+ struct tc_u_knode *new;
+
if (TC_U32_KEY(n->handle) == 0)
return -EINVAL;
- return u32_set_parms(net, tp, base,
- rtnl_dereference(n->ht_up), n, tb,
- tca[TCA_RATE], ovr);
+ new = u32_init_knode(tp, n);
+ if (!new)
+ return -ENOMEM;
+
+ err = u32_set_parms(net, tp, base,
+ rtnl_dereference(n->ht_up), new, tb,
+ tca[TCA_RATE], ovr);
+
+ if (err) {
+ u32_destroy_key(tp, new, false);
+ return err;
+ }
+
+ u32_replace_knode(tp, tp_c, new);
+ call_rcu(&n->rcu, u32_delete_key_rcu);
+ return 0;
}
if (tb[TCA_U32_DIVISOR]) {
--
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