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net/sched: act_police: fix race condition on state variables

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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 2d550dbad8 ("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: 2d550dbad8 ("net/sched: act_police: don't use spinlock in the data path")
Reported-and-suggested-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
This commit is contained in:
Davide Caratti 2018-11-20 22:18:44 +01:00 committed by David S. Miller
parent b1d9823301
commit f2cbd48528
1 changed files with 21 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

35
net/sched/act_police.c
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@ -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: