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Date: Tue, 25 Aug 2015 20:06:35 -0700
From: Alexei Starovoitov <ast@...mgrid.com>
To: "David S. Miller" <davem@...emloft.net>
Cc: Eric Dumazet <edumazet@...gle.com>,
Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org
Subject: [PATCH v2 net-next 5/5] net_sched: act_bpf: remove spinlock in fast path
Similar to act_gact/act_mirred, act_bpf can be lockless in packet processing
with extra care taken to free bpf programs after rcu grace period.
Replacement of existing act_bpf (very rare) is done with synchronize_rcu()
and final destruction is done from tc_action_ops->cleanup() callback that is
called from tcf_exts_destroy()->tcf_action_destroy()->__tcf_hash_release() when
bind and refcnt reach zero which is only possible when classifier is destroyed.
Previous two patches fixed the last two classifiers (tcindex and rsvp) to
call tcf_exts_destroy() from rcu callback.
Similar to gact/mirred there is a race between prog->filter and
prog->tcf_action. Meaning that the program being replaced may use
previous default action if it happened to return TC_ACT_UNSPEC.
act_mirred race betwen tcf_action and tcfm_dev is similar.
In all cases the race is harmless.
Long term we may want to improve the situation by replacing the whole
tc_action->priv as single pointer instead of updating inner fields one by one.
Signed-off-by: Alexei Starovoitov <ast@...mgrid.com>
---
include/net/tc_act/tc_bpf.h | 2 +-
net/sched/act_bpf.c | 36 +++++++++++++++++++-----------------
2 files changed, 20 insertions(+), 18 deletions(-)
diff --git a/include/net/tc_act/tc_bpf.h b/include/net/tc_act/tc_bpf.h
index a152e9858b2c..958d69cfb19c 100644
--- a/include/net/tc_act/tc_bpf.h
+++ b/include/net/tc_act/tc_bpf.h
@@ -15,7 +15,7 @@
struct tcf_bpf {
struct tcf_common common;
- struct bpf_prog *filter;
+ struct bpf_prog __rcu *filter;
union {
u32 bpf_fd;
u16 bpf_num_ops;
diff --git a/net/sched/act_bpf.c b/net/sched/act_bpf.c
index 458cf647e698..559bfa011bda 100644
--- a/net/sched/act_bpf.c
+++ b/net/sched/act_bpf.c
@@ -37,25 +37,24 @@ static int tcf_bpf(struct sk_buff *skb, const struct tc_action *act,
struct tcf_result *res)
{
struct tcf_bpf *prog = act->priv;
+ struct bpf_prog *filter;
int action, filter_res;
bool at_ingress = G_TC_AT(skb->tc_verd) & AT_INGRESS;
if (unlikely(!skb_mac_header_was_set(skb)))
return TC_ACT_UNSPEC;
- spin_lock(&prog->tcf_lock);
-
- prog->tcf_tm.lastuse = jiffies;
- bstats_update(&prog->tcf_bstats, skb);
+ tcf_lastuse_update(&prog->tcf_tm);
+ bstats_cpu_update(this_cpu_ptr(prog->common.cpu_bstats), skb);
- /* Needed here for accessing maps. */
rcu_read_lock();
+ filter = rcu_dereference(prog->filter);
if (at_ingress) {
__skb_push(skb, skb->mac_len);
- filter_res = BPF_PROG_RUN(prog->filter, skb);
+ filter_res = BPF_PROG_RUN(filter, skb);
__skb_pull(skb, skb->mac_len);
} else {
- filter_res = BPF_PROG_RUN(prog->filter, skb);
+ filter_res = BPF_PROG_RUN(filter, skb);
}
rcu_read_unlock();
@@ -77,7 +76,7 @@ static int tcf_bpf(struct sk_buff *skb, const struct tc_action *act,
break;
case TC_ACT_SHOT:
action = filter_res;
- prog->tcf_qstats.drops++;
+ qstats_drop_inc(this_cpu_ptr(prog->common.cpu_qstats));
break;
case TC_ACT_UNSPEC:
action = prog->tcf_action;
@@ -87,7 +86,6 @@ static int tcf_bpf(struct sk_buff *skb, const struct tc_action *act,
break;
}
- spin_unlock(&prog->tcf_lock);
return action;
}
@@ -263,7 +261,10 @@ static void tcf_bpf_prog_fill_cfg(const struct tcf_bpf *prog,
struct tcf_bpf_cfg *cfg)
{
cfg->is_ebpf = tcf_bpf_is_ebpf(prog);
- cfg->filter = prog->filter;
+ /* updates to prog->filter are prevented, since it's called either
+ * with rtnl lock or during final cleanup in rcu callback
+ */
+ cfg->filter = rcu_dereference_protected(prog->filter, 1);
cfg->bpf_ops = prog->bpf_ops;
cfg->bpf_name = prog->bpf_name;
@@ -294,7 +295,7 @@ static int tcf_bpf_init(struct net *net, struct nlattr *nla,
if (!tcf_hash_check(parm->index, act, bind)) {
ret = tcf_hash_create(parm->index, est, act,
- sizeof(*prog), bind, false);
+ sizeof(*prog), bind, true);
if (ret < 0)
return ret;
@@ -325,7 +326,7 @@ static int tcf_bpf_init(struct net *net, struct nlattr *nla,
goto out;
prog = to_bpf(act);
- spin_lock_bh(&prog->tcf_lock);
+ ASSERT_RTNL();
if (res != ACT_P_CREATED)
tcf_bpf_prog_fill_cfg(prog, &old);
@@ -339,14 +340,15 @@ static int tcf_bpf_init(struct net *net, struct nlattr *nla,
prog->bpf_fd = cfg.bpf_fd;
prog->tcf_action = parm->action;
- prog->filter = cfg.filter;
-
- spin_unlock_bh(&prog->tcf_lock);
+ rcu_assign_pointer(prog->filter, cfg.filter);
- if (res == ACT_P_CREATED)
+ if (res == ACT_P_CREATED) {
tcf_hash_insert(act);
- else
+ } else {
+ /* make sure the program being replaced is no longer executing */
+ synchronize_rcu();
tcf_bpf_cfg_cleanup(&old);
+ }
return res;
out:
--
1.7.9.5
--
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