net/sched: act_police: don't use spinlock in the data path

use RCU instead of spinlocks, to protect concurrent read/write on
act_police configuration. This reduces the effects of contention in the
data path, in case multiple readers are present.

Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sched/act_police.c b/net/sched/act_police.c
index 965a48d..92649d2 100644 (file)
--- a/net/sched/act_police.c
+++ b/net/sched/act_police.c
@@ -22,8 +22,7 @@
 #include <net/act_api.h>
 #include <net/netlink.h>
 
-struct tcf_police {
-       struct tc_action        common;
+struct tcf_police_params {
        int                     tcfp_result;
        u32                     tcfp_ewma_rate;
        s64                     tcfp_burst;
@@ -36,6 +35,12 @@ struct tcf_police {
        bool                    rate_present;
        struct psched_ratecfg   peak;
        bool                    peak_present;
+       struct rcu_head rcu;
+};
+
+struct tcf_police {
+       struct tc_action        common;
+       struct tcf_police_params __rcu *params;
 };
 
 #define to_police(pc) ((struct tcf_police *)pc)
@@ -84,6 +89,7 @@ static int tcf_police_init(struct net *net, struct nlattr *nla,
        struct tcf_police *police;
        struct qdisc_rate_table *R_tab = NULL, *P_tab = NULL;
        struct tc_action_net *tn = net_generic(net, police_net_id);
+       struct tcf_police_params *new;
        bool exists = false;
        int size;
 
@@ -151,50 +157,60 @@ static int tcf_police_init(struct net *net, struct nlattr *nla,
                goto failure;
        }
 
-       spin_lock_bh(&police->tcf_lock);
+       new = kzalloc(sizeof(*new), GFP_KERNEL);
+       if (unlikely(!new)) {
+               err = -ENOMEM;
+               goto failure;
+       }
+
        /* No failure allowed after this point */
-       police->tcfp_mtu = parm->mtu;
-       if (police->tcfp_mtu == 0) {
-               police->tcfp_mtu = ~0;
+       new->tcfp_mtu = parm->mtu;
+       if (!new->tcfp_mtu) {
+               new->tcfp_mtu = ~0;
                if (R_tab)
-                       police->tcfp_mtu = 255 << R_tab->rate.cell_log;
+                       new->tcfp_mtu = 255 << R_tab->rate.cell_log;
        }
        if (R_tab) {
-               police->rate_present = true;
-               psched_ratecfg_precompute(&police->rate, &R_tab->rate, 0);
+               new->rate_present = true;
+               psched_ratecfg_precompute(&new->rate, &R_tab->rate, 0);
                qdisc_put_rtab(R_tab);
        } else {
-               police->rate_present = false;
+               new->rate_present = false;
        }
        if (P_tab) {
-               police->peak_present = true;
-               psched_ratecfg_precompute(&police->peak, &P_tab->rate, 0);
+               new->peak_present = true;
+               psched_ratecfg_precompute(&new->peak, &P_tab->rate, 0);
                qdisc_put_rtab(P_tab);
        } else {
-               police->peak_present = false;
+               new->peak_present = false;
        }
 
        if (tb[TCA_POLICE_RESULT])
-               police->tcfp_result = nla_get_u32(tb[TCA_POLICE_RESULT]);
-       police->tcfp_burst = PSCHED_TICKS2NS(parm->burst);
-       police->tcfp_toks = police->tcfp_burst;
-       if (police->peak_present) {
-               police->tcfp_mtu_ptoks = (s64) psched_l2t_ns(&police->peak,
-                                                            police->tcfp_mtu);
-               police->tcfp_ptoks = police->tcfp_mtu_ptoks;
+               new->tcfp_result = nla_get_u32(tb[TCA_POLICE_RESULT]);
+       new->tcfp_burst = PSCHED_TICKS2NS(parm->burst);
+       new->tcfp_toks = new->tcfp_burst;
+       if (new->peak_present) {
+               new->tcfp_mtu_ptoks = (s64)psched_l2t_ns(&new->peak,
+                                                        new->tcfp_mtu);
+               new->tcfp_ptoks = new->tcfp_mtu_ptoks;
        }
-       police->tcf_action = parm->action;
 
        if (tb[TCA_POLICE_AVRATE])
-               police->tcfp_ewma_rate = nla_get_u32(tb[TCA_POLICE_AVRATE]);
+               new->tcfp_ewma_rate = nla_get_u32(tb[TCA_POLICE_AVRATE]);
 
+       spin_lock_bh(&police->tcf_lock);
+       new->tcfp_t_c = ktime_get_ns();
+       police->tcf_action = parm->action;
+       rcu_swap_protected(police->params,
+                          new,
+                          lockdep_is_held(&police->tcf_lock));
        spin_unlock_bh(&police->tcf_lock);
-       if (ret != ACT_P_CREATED)
-               return ret;
 
-       police->tcfp_t_c = ktime_get_ns();
-       tcf_idr_insert(tn, *a);
+       if (new)
+               kfree_rcu(new, rcu);
 
+       if (ret == ACT_P_CREATED)
+               tcf_idr_insert(tn, *a);
        return ret;
 
 failure:
@@ -208,68 +224,77 @@ static int tcf_police_act(struct sk_buff *skb, const struct tc_action *a,
                          struct tcf_result *res)
 {
        struct tcf_police *police = to_police(a);
+       struct tcf_police_params *p;
        s64 now, toks, ptoks = 0;
        int ret;
 
        tcf_lastuse_update(&police->tcf_tm);
        bstats_cpu_update(this_cpu_ptr(police->common.cpu_bstats), skb);
 
-       spin_lock(&police->tcf_lock);
-       if (police->tcfp_ewma_rate) {
+       ret = READ_ONCE(police->tcf_action);
+       p = rcu_dereference_bh(police->params);
+
+       if (p->tcfp_ewma_rate) {
                struct gnet_stats_rate_est64 sample;
 
                if (!gen_estimator_read(&police->tcf_rate_est, &sample) ||
-                   sample.bps >= police->tcfp_ewma_rate) {
-                       ret = police->tcf_action;
+                   sample.bps >= p->tcfp_ewma_rate)
                        goto inc_overlimits;
-               }
        }
 
-       if (qdisc_pkt_len(skb) <= police->tcfp_mtu) {
-               if (!police->rate_present) {
-                       ret = police->tcfp_result;
-                       goto unlock;
+       if (qdisc_pkt_len(skb) <= p->tcfp_mtu) {
+               if (!p->rate_present) {
+                       ret = p->tcfp_result;
+                       goto end;
                }
 
                now = ktime_get_ns();
-               toks = min_t(s64, now - police->tcfp_t_c,
-                            police->tcfp_burst);
-               if (police->peak_present) {
-                       ptoks = toks + police->tcfp_ptoks;
-                       if (ptoks > police->tcfp_mtu_ptoks)
-                               ptoks = police->tcfp_mtu_ptoks;
-                       ptoks -= (s64) psched_l2t_ns(&police->peak,
-                                                    qdisc_pkt_len(skb));
+               toks = min_t(s64, now - p->tcfp_t_c, p->tcfp_burst);
+               if (p->peak_present) {
+                       ptoks = toks + p->tcfp_ptoks;
+                       if (ptoks > p->tcfp_mtu_ptoks)
+                               ptoks = p->tcfp_mtu_ptoks;
+                       ptoks -= (s64)psched_l2t_ns(&p->peak,
+                                                   qdisc_pkt_len(skb));
                }
-               toks += police->tcfp_toks;
-               if (toks > police->tcfp_burst)
-                       toks = police->tcfp_burst;
-               toks -= (s64) psched_l2t_ns(&police->rate, qdisc_pkt_len(skb));
+               toks += p->tcfp_toks;
+               if (toks > p->tcfp_burst)
+                       toks = p->tcfp_burst;
+               toks -= (s64)psched_l2t_ns(&p->rate, qdisc_pkt_len(skb));
                if ((toks|ptoks) >= 0) {
-                       police->tcfp_t_c = now;
-                       police->tcfp_toks = toks;
-                       police->tcfp_ptoks = ptoks;
-                       ret = police->tcfp_result;
+                       p->tcfp_t_c = now;
+                       p->tcfp_toks = toks;
+                       p->tcfp_ptoks = ptoks;
+                       ret = p->tcfp_result;
                        goto inc_drops;
                }
        }
-       ret = police->tcf_action;
 
 inc_overlimits:
        qstats_overlimit_inc(this_cpu_ptr(police->common.cpu_qstats));
 inc_drops:
        if (ret == TC_ACT_SHOT)
                qstats_drop_inc(this_cpu_ptr(police->common.cpu_qstats));
-unlock:
-       spin_unlock(&police->tcf_lock);
+end:
        return ret;
 }
 
+static void tcf_police_cleanup(struct tc_action *a)
+{
+       struct tcf_police *police = to_police(a);
+       struct tcf_police_params *p;
+
+       p = rcu_dereference_protected(police->params, 1);
+       if (p)
+               kfree_rcu(p, rcu);
+}
+
 static int tcf_police_dump(struct sk_buff *skb, struct tc_action *a,
                               int bind, int ref)
 {
        unsigned char *b = skb_tail_pointer(skb);
        struct tcf_police *police = to_police(a);
+       struct tcf_police_params *p;
        struct tc_police opt = {
                .index = police->tcf_index,
                .refcnt = refcount_read(&police->tcf_refcnt) - ref,
@@ -279,19 +304,21 @@ static int tcf_police_dump(struct sk_buff *skb, struct tc_action *a,
 
        spin_lock_bh(&police->tcf_lock);
        opt.action = police->tcf_action;
-       opt.mtu = police->tcfp_mtu;
-       opt.burst = PSCHED_NS2TICKS(police->tcfp_burst);
-       if (police->rate_present)
-               psched_ratecfg_getrate(&opt.rate, &police->rate);
-       if (police->peak_present)
-               psched_ratecfg_getrate(&opt.peakrate, &police->peak);
+       p = rcu_dereference_protected(police->params,
+                                     lockdep_is_held(&police->tcf_lock));
+       opt.mtu = p->tcfp_mtu;
+       opt.burst = PSCHED_NS2TICKS(p->tcfp_burst);
+       if (p->rate_present)
+               psched_ratecfg_getrate(&opt.rate, &p->rate);
+       if (p->peak_present)
+               psched_ratecfg_getrate(&opt.peakrate, &p->peak);
        if (nla_put(skb, TCA_POLICE_TBF, sizeof(opt), &opt))
                goto nla_put_failure;
-       if (police->tcfp_result &&
-           nla_put_u32(skb, TCA_POLICE_RESULT, police->tcfp_result))
+       if (p->tcfp_result &&
+           nla_put_u32(skb, TCA_POLICE_RESULT, p->tcfp_result))
                goto nla_put_failure;
-       if (police->tcfp_ewma_rate &&
-           nla_put_u32(skb, TCA_POLICE_AVRATE, police->tcfp_ewma_rate))
+       if (p->tcfp_ewma_rate &&
+           nla_put_u32(skb, TCA_POLICE_AVRATE, p->tcfp_ewma_rate))
                goto nla_put_failure;
 
        t.install = jiffies_to_clock_t(jiffies - police->tcf_tm.install);
@@ -330,6 +357,7 @@ static struct tc_action_ops act_police_ops = {
        .init           =       tcf_police_init,
        .walk           =       tcf_police_walker,
        .lookup         =       tcf_police_search,
+       .cleanup        =       tcf_police_cleanup,
        .size           =       sizeof(struct tcf_police),
 };