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net_sched: introduce tcf_exts_get_net() and tcf_exts_put_net()

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Instead of holding netns refcnt in tc actions, we can minimize
the holding time by saving it in struct tcf_exts instead. This
means we can just hold netns refcnt right before call_rcu() and
release it after tcf_exts_destroy() is done.

However, because on netns cleanup path we call tcf_proto_destroy()
too, obviously we can not hold netns for a zero refcnt, in this
case we have to do cleanup synchronously. It is fine for RCU too,
the caller cleanup_net() already waits for a grace period.

For other cases, refcnt is non-zero and we can safely grab it as
normal and release it after we are done.

This patch provides two new API for each filter to use:
tcf_exts_get_net() and tcf_exts_put_net(). And all filters now can
use the following pattern:

void __destroy_filter() {
  tcf_exts_destroy();
  tcf_exts_put_net();  // <== release netns refcnt
  kfree();
}
void some_work() {
  rtnl_lock();
  __destroy_filter();
  rtnl_unlock();
}
void some_rcu_callback() {
  tcf_queue_work(some_work);
}

if (tcf_exts_get_net())  // <== hold netns refcnt
  call_rcu(some_rcu_callback);
else
  __destroy_filter();

Cc: Lucas Bates <lucasb@mojatatu.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Cong Wang 2017-11-06 13:47:19 -08:00 • committed by David S. Miller
parent c7e460ce55
commit e4b95c41df
2 changed files with 25 additions and 0 deletions
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24
include/net/pkt_cls.h
View file

@ -94,6 +94,7 @@ struct tcf_exts {
__u32 type; /* for backward compat(TCA_OLD_COMPAT) */
int nr_actions;
struct tc_action **actions;
struct net *net;
#endif
/* Map to export classifier specific extension TLV types to the
* generic extensions API. Unsupported extensions must be set to 0.
@ -107,6 +108,7 @@ static inline int tcf_exts_init(struct tcf_exts *exts, int action, int police)
#ifdef CONFIG_NET_CLS_ACT
exts->type = 0;
exts->nr_actions = 0;
exts->net = NULL;
exts->actions = kcalloc(TCA_ACT_MAX_PRIO, sizeof(struct tc_action *),
GFP_KERNEL);
if (!exts->actions)
@ -117,6 +119,28 @@ static inline int tcf_exts_init(struct tcf_exts *exts, int action, int police)
return 0;
}
/* Return false if the netns is being destroyed in cleanup_net(). Callers
* need to do cleanup synchronously in this case, otherwise may race with
* tc_action_net_exit(). Return true for other cases.
*/
static inline bool tcf_exts_get_net(struct tcf_exts *exts)
{
#ifdef CONFIG_NET_CLS_ACT
exts->net = maybe_get_net(exts->net);
return exts->net != NULL;
#else
return true;
#endif
}
static inline void tcf_exts_put_net(struct tcf_exts *exts)
{
#ifdef CONFIG_NET_CLS_ACT
if (exts->net)
put_net(exts->net);
#endif
}
static inline void tcf_exts_to_list(const struct tcf_exts *exts,
struct list_head *actions)
{

1
net/sched/cls_api.c
View file

@ -927,6 +927,7 @@ int tcf_exts_validate(struct net *net, struct tcf_proto *tp, struct nlattr **tb,
exts->actions[i++] = act;
exts->nr_actions = i;
}
exts->net = net;
}
#else
if ((exts->action && tb[exts->action]) ||