From d7fb60b9cafb982cb2e46a267646a8dfd4f2e5da Mon Sep 17 00:00:00 2001 From: Cong Wang Date: Mon, 11 Sep 2017 16:33:30 -0700 Subject: [PATCH] net_sched: get rid of tcfa_rcu gen estimator has been rewritten in commit 1c0d32fde5bd ("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 Cc: Jamal Hadi Salim Cc: Eric Dumazet Signed-off-by: Cong Wang Signed-off-by: David S. Miller --- include/net/act_api.h | 2 -- net/sched/act_api.c | 17 ++++++++--------- 2 files changed, 8 insertions(+), 11 deletions(-) diff --git a/include/net/act_api.h b/include/net/act_api.h index 8f3d5d8b5ae0..b944e0eb93be 100644 --- a/include/net/act_api.h +++ b/include/net/act_api.h @@ -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. diff --git a/net/sched/act_api.c b/net/sched/act_api.c index a306974e2fb4..fcd7dc7b807a 100644 --- a/net/sched/act_api.c +++ b/net/sched/act_api.c @@ -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); -- 2.30.2