net: sched: make cls_u32 lockless

Make cls_u32 classifier safe to run without holding lock. This patch
converts statistics that are kept in read section u32_classify into
per cpu counters.

This patch was tested with a tight u32 filter add/delete loop while
generating traffic with pktgen. By running pktgen on vlan devices
created on top of a physical device we can hit the qdisc layer
correctly. For ingress qdisc's a loopback cable was used.

for i in {1..100}; do
        q=`echo $i%8|bc`;
        echo -n "u32 tos: iteration $i on queue $q";
        tc filter add dev p3p2 parent $p prio $i u32 match ip tos 0x10 0xff \
                  action skbedit queue_mapping $q;
        sleep 1;
        tc filter del dev p3p2 prio $i;

        echo -n "u32 tos hash table: iteration $i on queue $q";
        tc filter add dev p3p2 parent $p protocol ip prio $i handle 628: u32 divisor 1
        tc filter add dev p3p2 parent $p protocol ip prio $i u32 \
                match ip protocol 17 0xff link 628: offset at 0 mask 0xf00 shift 6 plus 0
        tc filter add dev p3p2 parent $p protocol ip prio $i u32 \
                ht 628:0 match ip tos 0x10 0xff action skbedit queue_mapping $q
        sleep 2;
        tc filter del dev p3p2 prio $i
        sleep 1;
done

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index f3227d73a7aea0980bb46b7c5941cb2001763e69..5ed5ac4361b135896331c892fdfd1021706a5869 100644 (file)
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -36,6 +36,7 @@
 #include <linux/kernel.h>
 #include <linux/string.h>
 #include <linux/errno.h>
+#include <linux/percpu.h>
 #include <linux/rtnetlink.h>
 #include <linux/skbuff.h>
 #include <linux/bitmap.h>
@@ -44,16 +45,16 @@
 #include <net/pkt_cls.h>
 
 struct tc_u_knode {
-       struct tc_u_knode       *next;
+       struct tc_u_knode __rcu *next;
        u32                     handle;
-       struct tc_u_hnode       *ht_up;
+       struct tc_u_hnode __rcu *ht_up;
        struct tcf_exts         exts;
 #ifdef CONFIG_NET_CLS_IND
        int                     ifindex;
 #endif
        u8                      fshift;
        struct tcf_result       res;
-       struct tc_u_hnode       *ht_down;
+       struct tc_u_hnode __rcu *ht_down;
 #ifdef CONFIG_CLS_U32_PERF
        struct tc_u32_pcnt __percpu *pf;
 #endif
@@ -62,24 +63,28 @@ struct tc_u_knode {
        u32                     mask;
        u32 __percpu            *pcpu_success;
 #endif
+       struct tcf_proto        *tp;
        struct tc_u32_sel       sel;
+       struct rcu_head         rcu;
 };
 
 struct tc_u_hnode {
-       struct tc_u_hnode       *next;
+       struct tc_u_hnode __rcu *next;
        u32                     handle;
        u32                     prio;
        struct tc_u_common      *tp_c;
        int                     refcnt;
        unsigned int            divisor;
-       struct tc_u_knode       *ht[1];
+       struct tc_u_knode __rcu *ht[1];
+       struct rcu_head         rcu;
 };
 
 struct tc_u_common {
-       struct tc_u_hnode       *hlist;
+       struct tc_u_hnode __rcu *hlist;
        struct Qdisc            *q;
        int                     refcnt;
        u32                     hgenerator;
+       struct rcu_head         rcu;
 };
 
 static inline unsigned int u32_hash_fold(__be32 key,
@@ -98,7 +103,7 @@ static int u32_classify(struct sk_buff *skb, const struct tcf_proto *tp, struct
                unsigned int      off;
        } stack[TC_U32_MAXDEPTH];
 
-       struct tc_u_hnode *ht = tp->root;
+       struct tc_u_hnode *ht = rcu_dereference_bh(tp->root);
        unsigned int off = skb_network_offset(skb);
        struct tc_u_knode *n;
        int sdepth = 0;
@@ -110,7 +115,7 @@ static int u32_classify(struct sk_buff *skb, const struct tcf_proto *tp, struct
        int i, r;
 
 next_ht:
-       n = ht->ht[sel];
+       n = rcu_dereference_bh(ht->ht[sel]);
 
 next_knode:
        if (n) {
@@ -123,7 +128,7 @@ next_knode:
 
 #ifdef CONFIG_CLS_U32_MARK
                if ((skb->mark & n->mask) != n->val) {
-                       n = n->next;
+                       n = rcu_dereference_bh(n->next);
                        goto next_knode;
                } else {
                        __this_cpu_inc(*n->pcpu_success);
@@ -141,7 +146,7 @@ next_knode:
                        if (!data)
                                goto out;
                        if ((*data ^ key->val) & key->mask) {
-                               n = n->next;
+                               n = rcu_dereference_bh(n->next);
                                goto next_knode;
                        }
 #ifdef CONFIG_CLS_U32_PERF
@@ -149,14 +154,16 @@ next_knode:
                        j++;
 #endif
                }
-               if (n->ht_down == NULL) {
+
+               ht = rcu_dereference_bh(n->ht_down);
+               if (!ht) {
 check_terminal:
                        if (n->sel.flags & TC_U32_TERMINAL) {
 
                                *res = n->res;
 #ifdef CONFIG_NET_CLS_IND
                                if (!tcf_match_indev(skb, n->ifindex)) {
-                                       n = n->next;
+                                       n = rcu_dereference_bh(n->next);
                                        goto next_knode;
                                }
 #endif
@@ -165,13 +172,13 @@ check_terminal:
 #endif
                                r = tcf_exts_exec(skb, &n->exts, res);
                                if (r < 0) {
-                                       n = n->next;
+                                       n = rcu_dereference_bh(n->next);
                                        goto next_knode;
                                }
 
                                return r;
                        }
-                       n = n->next;
+                       n = rcu_dereference_bh(n->next);
                        goto next_knode;
                }
 
@@ -182,7 +189,7 @@ check_terminal:
                stack[sdepth].off = off;
                sdepth++;
 
-               ht = n->ht_down;
+               ht = rcu_dereference_bh(n->ht_down);
                sel = 0;
                if (ht->divisor) {
                        __be32 *data, hdata;
@@ -224,7 +231,7 @@ check_terminal:
        /* POP */
        if (sdepth--) {
                n = stack[sdepth].knode;
-               ht = n->ht_up;
+               ht = rcu_dereference_bh(n->ht_up);
                off = stack[sdepth].off;
                goto check_terminal;
        }
@@ -241,7 +248,9 @@ u32_lookup_ht(struct tc_u_common *tp_c, u32 handle)
 {
        struct tc_u_hnode *ht;
 
-       for (ht = tp_c->hlist; ht; ht = ht->next)
+       for (ht = rtnl_dereference(tp_c->hlist);
+            ht;
+            ht = rtnl_dereference(ht->next))
                if (ht->handle == handle)
                        break;
 
@@ -258,7 +267,9 @@ u32_lookup_key(struct tc_u_hnode *ht, u32 handle)
        if (sel > ht->divisor)
                goto out;
 
-       for (n = ht->ht[sel]; n; n = n->next)
+       for (n = rtnl_dereference(ht->ht[sel]);
+            n;
+            n = rtnl_dereference(n->next))
                if (n->handle == handle)
                        break;
 out:
@@ -272,7 +283,7 @@ static unsigned long u32_get(struct tcf_proto *tp, u32 handle)
        struct tc_u_common *tp_c = tp->data;
 
        if (TC_U32_HTID(handle) == TC_U32_ROOT)
-               ht = tp->root;
+               ht = rtnl_dereference(tp->root);
        else
                ht = u32_lookup_ht(tp_c, TC_U32_HTID(handle));
 
@@ -293,6 +304,9 @@ static u32 gen_new_htid(struct tc_u_common *tp_c)
 {
        int i = 0x800;
 
+       /* hgenerator only used inside rtnl lock it is safe to increment
+        * without read _copy_ update semantics
+        */
        do {
                if (++tp_c->hgenerator == 0x7FF)
                        tp_c->hgenerator = 1;
@@ -328,11 +342,11 @@ static int u32_init(struct tcf_proto *tp)
        }
 
        tp_c->refcnt++;
-       root_ht->next = tp_c->hlist;
-       tp_c->hlist = root_ht;
+       RCU_INIT_POINTER(root_ht->next, tp_c->hlist);
+       rcu_assign_pointer(tp_c->hlist, root_ht);
        root_ht->tp_c = tp_c;
 
-       tp->root = root_ht;
+       rcu_assign_pointer(tp->root, root_ht);
        tp->data = tp_c;
        return 0;
 }
@@ -350,19 +364,27 @@ static int u32_destroy_key(struct tcf_proto *tp, struct tc_u_knode *n)
        return 0;
 }
 
+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);
+}
+
 static int u32_delete_key(struct tcf_proto *tp, struct tc_u_knode *key)
 {
-       struct tc_u_knode **kp;
+       struct tc_u_knode __rcu **kp;
+       struct tc_u_knode *pkp;
        struct tc_u_hnode *ht = key->ht_up;
 
        if (ht) {
-               for (kp = &ht->ht[TC_U32_HASH(key->handle)]; *kp; kp = &(*kp)->next) {
-                       if (*kp == key) {
-                               tcf_tree_lock(tp);
-                               *kp = key->next;
-                               tcf_tree_unlock(tp);
+               kp = &ht->ht[TC_U32_HASH(key->handle)];
+               for (pkp = rtnl_dereference(*kp); pkp;
+                    kp = &pkp->next, pkp = rtnl_dereference(*kp)) {
+                       if (pkp == key) {
+                               RCU_INIT_POINTER(*kp, key->next);
 
-                               u32_destroy_key(tp, key);
+                               call_rcu(&key->rcu, u32_delete_key_rcu);
                                return 0;
                        }
                }
@@ -371,16 +393,16 @@ static int u32_delete_key(struct tcf_proto *tp, struct tc_u_knode *key)
        return 0;
 }
 
-static void u32_clear_hnode(struct tcf_proto *tp, struct tc_u_hnode *ht)
+static void u32_clear_hnode(struct tc_u_hnode *ht)
 {
        struct tc_u_knode *n;
        unsigned int h;
 
        for (h = 0; h <= ht->divisor; h++) {
-               while ((n = ht->ht[h]) != NULL) {
-                       ht->ht[h] = n->next;
-
-                       u32_destroy_key(tp, n);
+               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);
                }
        }
 }
@@ -388,28 +410,31 @@ static void u32_clear_hnode(struct tcf_proto *tp, struct tc_u_hnode *ht)
 static int u32_destroy_hnode(struct tcf_proto *tp, struct tc_u_hnode *ht)
 {
        struct tc_u_common *tp_c = tp->data;
-       struct tc_u_hnode **hn;
+       struct tc_u_hnode __rcu **hn;
+       struct tc_u_hnode *phn;
 
        WARN_ON(ht->refcnt);
 
-       u32_clear_hnode(tp, ht);
+       u32_clear_hnode(ht);
 
-       for (hn = &tp_c->hlist; *hn; hn = &(*hn)->next) {
-               if (*hn == ht) {
-                       *hn = ht->next;
-                       kfree(ht);
+       hn = &tp_c->hlist;
+       for (phn = rtnl_dereference(*hn);
+            phn;
+            hn = &phn->next, phn = rtnl_dereference(*hn)) {
+               if (phn == ht) {
+                       RCU_INIT_POINTER(*hn, ht->next);
+                       kfree_rcu(ht, rcu);
                        return 0;
                }
        }
 
-       WARN_ON(1);
        return -ENOENT;
 }
 
 static void u32_destroy(struct tcf_proto *tp)
 {
        struct tc_u_common *tp_c = tp->data;
-       struct tc_u_hnode *root_ht = tp->root;
+       struct tc_u_hnode *root_ht = rtnl_dereference(tp->root);
 
        WARN_ON(root_ht == NULL);
 
@@ -421,17 +446,16 @@ static void u32_destroy(struct tcf_proto *tp)
 
                tp->q->u32_node = NULL;
 
-               for (ht = tp_c->hlist; ht; ht = ht->next) {
+               for (ht = rtnl_dereference(tp_c->hlist);
+                    ht;
+                    ht = rtnl_dereference(ht->next)) {
                        ht->refcnt--;
-                       u32_clear_hnode(tp, ht);
+                       u32_clear_hnode(ht);
                }
 
-               while ((ht = tp_c->hlist) != NULL) {
-                       tp_c->hlist = ht->next;
-
-                       WARN_ON(ht->refcnt != 0);
-
-                       kfree(ht);
+               while ((ht = rtnl_dereference(tp_c->hlist)) != NULL) {
+                       RCU_INIT_POINTER(tp_c->hlist, ht->next);
+                       kfree_rcu(ht, rcu);
                }
 
                kfree(tp_c);
@@ -443,6 +467,7 @@ static void u32_destroy(struct tcf_proto *tp)
 static int u32_delete(struct tcf_proto *tp, unsigned long arg)
 {
        struct tc_u_hnode *ht = (struct tc_u_hnode *)arg;
+       struct tc_u_hnode *root_ht = rtnl_dereference(tp->root);
 
        if (ht == NULL)
                return 0;
@@ -450,7 +475,7 @@ static int u32_delete(struct tcf_proto *tp, unsigned long arg)
        if (TC_U32_KEY(ht->handle))
                return u32_delete_key(tp, (struct tc_u_knode *)ht);
 
-       if (tp->root == ht)
+       if (root_ht == ht)
                return -EINVAL;
 
        if (ht->refcnt == 1) {
@@ -473,7 +498,9 @@ static u32 gen_new_kid(struct tc_u_hnode *ht, u32 handle)
        if (!bitmap)
                return handle | 0xFFF;
 
-       for (n = ht->ht[TC_U32_HASH(handle)]; n; n = n->next)
+       for (n = rtnl_dereference(ht->ht[TC_U32_HASH(handle)]);
+            n;
+            n = rtnl_dereference(n->next))
                set_bit(TC_U32_NODE(n->handle), bitmap);
 
        i = find_next_zero_bit(bitmap, NR_U32_NODE, 0x800);
@@ -523,10 +550,8 @@ static int u32_set_parms(struct net *net, struct tcf_proto *tp,
                        ht_down->refcnt++;
                }
 
-               tcf_tree_lock(tp);
-               ht_old = n->ht_down;
-               n->ht_down = ht_down;
-               tcf_tree_unlock(tp);
+               ht_old = rtnl_dereference(n->ht_down);
+               rcu_assign_pointer(n->ht_down, ht_down);
 
                if (ht_old)
                        ht_old->refcnt--;
@@ -606,8 +631,8 @@ static int u32_change(struct net *net, struct sk_buff *in_skb,
                ht->divisor = divisor;
                ht->handle = handle;
                ht->prio = tp->prio;
-               ht->next = tp_c->hlist;
-               tp_c->hlist = ht;
+               RCU_INIT_POINTER(ht->next, tp_c->hlist);
+               rcu_assign_pointer(tp_c->hlist, ht);
                *arg = (unsigned long)ht;
                return 0;
        }
@@ -615,7 +640,7 @@ static int u32_change(struct net *net, struct sk_buff *in_skb,
        if (tb[TCA_U32_HASH]) {
                htid = nla_get_u32(tb[TCA_U32_HASH]);
                if (TC_U32_HTID(htid) == TC_U32_ROOT) {
-                       ht = tp->root;
+                       ht = rtnl_dereference(tp->root);
                        htid = ht->handle;
                } else {
                        ht = u32_lookup_ht(tp->data, TC_U32_HTID(htid));
@@ -623,7 +648,7 @@ static int u32_change(struct net *net, struct sk_buff *in_skb,
                                return -EINVAL;
                }
        } else {
-               ht = tp->root;
+               ht = rtnl_dereference(tp->root);
                htid = ht->handle;
        }
 
@@ -660,6 +685,7 @@ static int u32_change(struct net *net, struct sk_buff *in_skb,
        n->handle = handle;
        n->fshift = s->hmask ? ffs(ntohl(s->hmask)) - 1 : 0;
        tcf_exts_init(&n->exts, TCA_U32_ACT, TCA_U32_POLICE);
+       n->tp = tp;
 
 #ifdef CONFIG_CLS_U32_MARK
        n->pcpu_success = alloc_percpu(u32);
@@ -675,21 +701,23 @@ static int u32_change(struct net *net, struct sk_buff *in_skb,
 
        err = u32_set_parms(net, tp, base, ht, n, tb, tca[TCA_RATE], ovr);
        if (err == 0) {
-               struct tc_u_knode **ins;
-               for (ins = &ht->ht[TC_U32_HASH(handle)]; *ins; ins = &(*ins)->next)
-                       if (TC_U32_NODE(handle) < TC_U32_NODE((*ins)->handle))
+               struct tc_u_knode __rcu **ins;
+               struct tc_u_knode *pins;
+
+               ins = &ht->ht[TC_U32_HASH(handle)];
+               for (pins = rtnl_dereference(*ins); pins;
+                    ins = &pins->next, pins = rtnl_dereference(*ins))
+                       if (TC_U32_NODE(handle) < TC_U32_NODE(pins->handle))
                                break;
 
-               n->next = *ins;
-               tcf_tree_lock(tp);
-               *ins = n;
-               tcf_tree_unlock(tp);
+               RCU_INIT_POINTER(n->next, pins);
+               rcu_assign_pointer(*ins, n);
 
                *arg = (unsigned long)n;
                return 0;
        }
 #ifdef CONFIG_CLS_U32_PERF
-       kfree(n->pf);
+       free_percpu(n->pf);
 #endif
        kfree(n);
        return err;
@@ -705,7 +733,9 @@ static void u32_walk(struct tcf_proto *tp, struct tcf_walker *arg)
        if (arg->stop)
                return;
 
-       for (ht = tp_c->hlist; ht; ht = ht->next) {
+       for (ht = rtnl_dereference(tp_c->hlist);
+            ht;
+            ht = rtnl_dereference(ht->next)) {
                if (ht->prio != tp->prio)
                        continue;
                if (arg->count >= arg->skip) {
@@ -716,7 +746,9 @@ static void u32_walk(struct tcf_proto *tp, struct tcf_walker *arg)
                }
                arg->count++;
                for (h = 0; h <= ht->divisor; h++) {
-                       for (n = ht->ht[h]; n; n = n->next) {
+                       for (n = rtnl_dereference(ht->ht[h]);
+                            n;
+                            n = rtnl_dereference(n->next)) {
                                if (arg->count < arg->skip) {
                                        arg->count++;
                                        continue;
@@ -735,6 +767,7 @@ static int u32_dump(struct net *net, struct tcf_proto *tp, unsigned long fh,
                     struct sk_buff *skb, struct tcmsg *t)
 {
        struct tc_u_knode *n = (struct tc_u_knode *)fh;
+       struct tc_u_hnode *ht_up, *ht_down;
        struct nlattr *nest;
 
        if (n == NULL)
@@ -762,7 +795,9 @@ static int u32_dump(struct net *net, struct tcf_proto *tp, unsigned long fh,
                            sizeof(n->sel) + n->sel.nkeys*sizeof(struct tc_u32_key),
                            &n->sel))
                        goto nla_put_failure;
-               if (n->ht_up) {
+
+               ht_up = rtnl_dereference(n->ht_up);
+               if (ht_up) {
                        u32 htid = n->handle & 0xFFFFF000;
                        if (nla_put_u32(skb, TCA_U32_HASH, htid))
                                goto nla_put_failure;
@@ -770,8 +805,10 @@ static int u32_dump(struct net *net, struct tcf_proto *tp, unsigned long fh,
                if (n->res.classid &&
                    nla_put_u32(skb, TCA_U32_CLASSID, n->res.classid))
                        goto nla_put_failure;
-               if (n->ht_down &&
-                   nla_put_u32(skb, TCA_U32_LINK, n->ht_down->handle))
+
+               ht_down = rtnl_dereference(n->ht_down);
+               if (ht_down &&
+                   nla_put_u32(skb, TCA_U32_LINK, ht_down->handle))
                        goto nla_put_failure;
 
 #ifdef CONFIG_CLS_U32_MARK