From f2cbd485282014132851bf37cb2ca624a456275d Mon Sep 17 00:00:00 2001 From: Davide Caratti Date: Tue, 20 Nov 2018 22:18:44 +0100 Subject: [PATCH] net/sched: act_police: fix race condition on state variables after 'police' configuration parameters were converted to use RCU instead of spinlock, the state variables used to compute the traffic rate (namely 'tcfp_toks', 'tcfp_ptoks' and 'tcfp_t_c') are erroneously read/updated in the traffic path without any protection. Use a dedicated spinlock to avoid race conditions on these variables, and ensure proper cache-line alignment. In this way, 'police' is still faster than what we observed when 'tcf_lock' was used in the traffic path _ i.e. reverting commit 2d550dbad83c ("net/sched: act_police: don't use spinlock in the data path"). Moreover, we preserve the throughput improvement that was obtained after 'police' started using per-cpu counters, when 'avrate' is used instead of 'rate'. Changes since v1 (thanks to Eric Dumazet): - call ktime_get_ns() before acquiring the lock in the traffic path - use a dedicated spinlock instead of tcf_lock - improve cache-line usage Fixes: 2d550dbad83c ("net/sched: act_police: don't use spinlock in the data path") Reported-and-suggested-by: Eric Dumazet Signed-off-by: Davide Caratti Reviewed-by: Eric Dumazet --- net/sched/act_police.c | 35 +++++++++++++++++++++-------------- 1 file changed, 21 insertions(+), 14 deletions(-) diff --git a/net/sched/act_police.c b/net/sched/act_police.c index 052855d47354..ee4665a5a022 100644 --- a/net/sched/act_police.c +++ b/net/sched/act_police.c @@ -27,10 +27,7 @@ struct tcf_police_params { u32 tcfp_ewma_rate; s64 tcfp_burst; u32 tcfp_mtu; - s64 tcfp_toks; - s64 tcfp_ptoks; s64 tcfp_mtu_ptoks; - s64 tcfp_t_c; struct psched_ratecfg rate; bool rate_present; struct psched_ratecfg peak; @@ -41,6 +38,11 @@ struct tcf_police_params { struct tcf_police { struct tc_action common; struct tcf_police_params __rcu *params; + + spinlock_t tcfp_lock ____cacheline_aligned_in_smp; + s64 tcfp_toks; + s64 tcfp_ptoks; + s64 tcfp_t_c; }; #define to_police(pc) ((struct tcf_police *)pc) @@ -186,12 +188,9 @@ static int tcf_police_init(struct net *net, struct nlattr *nla, } new->tcfp_burst = PSCHED_TICKS2NS(parm->burst); - new->tcfp_toks = new->tcfp_burst; - if (new->peak_present) { + if (new->peak_present) new->tcfp_mtu_ptoks = (s64)psched_l2t_ns(&new->peak, new->tcfp_mtu); - new->tcfp_ptoks = new->tcfp_mtu_ptoks; - } if (tb[TCA_POLICE_AVRATE]) new->tcfp_ewma_rate = nla_get_u32(tb[TCA_POLICE_AVRATE]); @@ -207,7 +206,12 @@ static int tcf_police_init(struct net *net, struct nlattr *nla, } spin_lock_bh(&police->tcf_lock); - new->tcfp_t_c = ktime_get_ns(); + spin_lock_bh(&police->tcfp_lock); + police->tcfp_t_c = ktime_get_ns(); + police->tcfp_toks = new->tcfp_burst; + if (new->peak_present) + police->tcfp_ptoks = new->tcfp_mtu_ptoks; + spin_unlock_bh(&police->tcfp_lock); police->tcf_action = parm->action; rcu_swap_protected(police->params, new, @@ -257,25 +261,28 @@ static int tcf_police_act(struct sk_buff *skb, const struct tc_action *a, } now = ktime_get_ns(); - toks = min_t(s64, now - p->tcfp_t_c, p->tcfp_burst); + spin_lock_bh(&police->tcfp_lock); + toks = min_t(s64, now - police->tcfp_t_c, p->tcfp_burst); if (p->peak_present) { - ptoks = toks + p->tcfp_ptoks; + ptoks = toks + police->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 += p->tcfp_toks; + toks += police->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) { - p->tcfp_t_c = now; - p->tcfp_toks = toks; - p->tcfp_ptoks = ptoks; + police->tcfp_t_c = now; + police->tcfp_toks = toks; + police->tcfp_ptoks = ptoks; + spin_unlock_bh(&police->tcfp_lock); ret = p->tcfp_result; goto inc_drops; } + spin_unlock_bh(&police->tcfp_lock); } inc_overlimits: