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net_sched: get rid of tcfa_rcu

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gen estimator has been rewritten in commit 1c0d32fde5
("net_sched: gen_estimator: complete rewrite of rate estimators"),
the caller is no longer needed to wait for a grace period.
So this patch gets rid of it.

This also completely closes a race condition between action free
path and filter chain add/remove path for the following patch.
Because otherwise the nested RCU callback can't be caught by
rcu_barrier().

Please see also the comments in code.

Cc: Jiri Pirko <jiri@mellanox.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Eric Dumazet <edumazet@google.com>
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 2017-09-11 16:33:30 -07:00 committed by David S. Miller
parent da8ab57863
commit d7fb60b9ca
2 changed files with 8 additions and 11 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

2
include/net/act_api.h
View file

@ -34,7 +34,6 @@ struct tc_action {
struct gnet_stats_queue tcfa_qstats;
struct net_rate_estimator __rcu *tcfa_rate_est;
spinlock_t tcfa_lock;
struct rcu_head tcfa_rcu;
struct gnet_stats_basic_cpu __percpu *cpu_bstats;
struct gnet_stats_queue __percpu *cpu_qstats;
struct tc_cookie *act_cookie;
@ -50,7 +49,6 @@ struct tc_action {
#define tcf_qstats common.tcfa_qstats
#define tcf_rate_est common.tcfa_rate_est
#define tcf_lock common.tcfa_lock
#define tcf_rcu common.tcfa_rcu
/* Update lastuse only if needed, to avoid dirtying a cache line.
* We use a temp variable to avoid fetching jiffies twice.

17
net/sched/act_api.c
View file

@ -53,10 +53,13 @@ static void tcf_action_goto_chain_exec(const struct tc_action *a,
res->goto_tp = rcu_dereference_bh(chain->filter_chain);
}
static void free_tcf(struct rcu_head *head)
/* XXX: For standalone actions, we don't need a RCU grace period either, because
* actions are always connected to filters and filters are already destroyed in
* RCU callbacks, so after a RCU grace period actions are already disconnected
* from filters. Readers later can not find us.
*/
static void free_tcf(struct tc_action *p)
{
struct tc_action *p = container_of(head, struct tc_action, tcfa_rcu);
free_percpu(p->cpu_bstats);
free_percpu(p->cpu_qstats);
@ -76,11 +79,7 @@ static void tcf_idr_remove(struct tcf_idrinfo *idrinfo, struct tc_action *p)
idr_remove_ext(&idrinfo->action_idr, p->tcfa_index);
spin_unlock_bh(&idrinfo->lock);
gen_kill_estimator(&p->tcfa_rate_est);
/*
* gen_estimator est_timer() might access p->tcfa_lock
* or bstats, wait a RCU grace period before freeing p
*/
call_rcu(&p->tcfa_rcu, free_tcf);
free_tcf(p);
}
int __tcf_idr_release(struct tc_action *p, bool bind, bool strict)
@ -259,7 +258,7 @@ void tcf_idr_cleanup(struct tc_action *a, struct nlattr *est)
{
if (est)
gen_kill_estimator(&a->tcfa_rate_est);
call_rcu(&a->tcfa_rcu, free_tcf);
free_tcf(a);
}
EXPORT_SYMBOL(tcf_idr_cleanup);