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Date: Wed, 9 Jun 2010 12:50:35 +0000
From: Jarek Poplawski <jarkao2@...il.com>
To: Eric Dumazet <eric.dumazet@...il.com>
Cc: Changli Gao <xiaosuo@...il.com>,
David Miller <davem@...emloft.net>,
netdev <netdev@...r.kernel.org>,
Stephen Hemminger <shemminger@...tta.com>,
Patrick McHardy <kaber@...sh.net>
Subject: Re: [PATCH] pkt_sched: gen_kill_estimator() rcu fixes
On Wed, Jun 09, 2010 at 02:09:23PM +0200, Eric Dumazet wrote:
> Le mercredi 09 juin 2010 ?? 10:41 +0000, Jarek Poplawski a écrit :
>
> > Spelling suggestion: xt_rateest_free_rcu?
> >
> > Since it's only 3 places I'd consider adding little comments,
> > who needs this call_rcu (like in qdisc_destroy).
> >
> > Anyway this patch looks OK to me.
> >
>
> Thanks for reviewing, you are right about typo and adding some comments.
>
> What about following ?
Very nice! (But let's remember these comments aren't very precise
wrt. bstats at the moment ;-)
Thanks,
Jarek P.
>
> [PATCH v2] pkt_sched: gen_kill_estimator() rcu fixes
>
> gen_kill_estimator() API is incomplete or not well documented, since
> caller should make sure an RCU grace period is respected before
> freeing stats_lock.
>
> This was partially addressed in commit 5d944c640b4
> (gen_estimator: deadlock fix), but same problem exist for all
> gen_kill_estimator() users, if lock they use is not already RCU
> protected.
>
> A code review shows xt_RATEEST.c, act_api.c, act_police.c have this
> problem. Other are ok because they use qdisc lock, already RCU
> protected.
>
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> ---
> include/net/act_api.h | 2 ++
> include/net/netfilter/xt_rateest.h | 1 +
> net/core/gen_estimator.c | 1 +
> net/netfilter/xt_RATEEST.c | 12 +++++++++++-
> net/sched/act_api.c | 11 ++++++++++-
> net/sched/act_police.c | 12 +++++++++++-
> 6 files changed, 36 insertions(+), 3 deletions(-)
>
> diff --git a/include/net/act_api.h b/include/net/act_api.h
> index c05fd71..bab385f 100644
> --- a/include/net/act_api.h
> +++ b/include/net/act_api.h
> @@ -20,6 +20,7 @@ struct tcf_common {
> struct gnet_stats_queue tcfc_qstats;
> struct gnet_stats_rate_est tcfc_rate_est;
> spinlock_t tcfc_lock;
> + struct rcu_head tcfc_rcu;
> };
> #define tcf_next common.tcfc_next
> #define tcf_index common.tcfc_index
> @@ -32,6 +33,7 @@ struct tcf_common {
> #define tcf_qstats common.tcfc_qstats
> #define tcf_rate_est common.tcfc_rate_est
> #define tcf_lock common.tcfc_lock
> +#define tcf_rcu common.tcfc_rcu
>
> struct tcf_police {
> struct tcf_common common;
> diff --git a/include/net/netfilter/xt_rateest.h b/include/net/netfilter/xt_rateest.h
> index ddbf37e..5e14277 100644
> --- a/include/net/netfilter/xt_rateest.h
> +++ b/include/net/netfilter/xt_rateest.h
> @@ -9,6 +9,7 @@ struct xt_rateest {
> struct gnet_estimator params;
> struct gnet_stats_rate_est rstats;
> struct gnet_stats_basic_packed bstats;
> + struct rcu_head rcu;
> };
>
> extern struct xt_rateest *xt_rateest_lookup(const char *name);
> diff --git a/net/core/gen_estimator.c b/net/core/gen_estimator.c
> index 785e527..9fbe7f7 100644
> --- a/net/core/gen_estimator.c
> +++ b/net/core/gen_estimator.c
> @@ -263,6 +263,7 @@ static void __gen_kill_estimator(struct rcu_head *head)
> *
> * Removes the rate estimator specified by &bstats and &rate_est.
> *
> + * Note : Caller should respect an RCU grace period before freeing stats_lock
> */
> void gen_kill_estimator(struct gnet_stats_basic_packed *bstats,
> struct gnet_stats_rate_est *rate_est)
> diff --git a/net/netfilter/xt_RATEEST.c b/net/netfilter/xt_RATEEST.c
> index 69c01e1..de079ab 100644
> --- a/net/netfilter/xt_RATEEST.c
> +++ b/net/netfilter/xt_RATEEST.c
> @@ -60,13 +60,22 @@ struct xt_rateest *xt_rateest_lookup(const char *name)
> }
> EXPORT_SYMBOL_GPL(xt_rateest_lookup);
>
> +static void xt_rateest_free_rcu(struct rcu_head *head)
> +{
> + kfree(container_of(head, struct xt_rateest, rcu));
> +}
> +
> void xt_rateest_put(struct xt_rateest *est)
> {
> mutex_lock(&xt_rateest_mutex);
> if (--est->refcnt == 0) {
> hlist_del(&est->list);
> gen_kill_estimator(&est->bstats, &est->rstats);
> - kfree(est);
> + /*
> + * gen_estimator est_timer() might access est->lock or bstats,
> + * wait a RCU grace period before freeing 'est'
> + */
> + call_rcu(&est->rcu, xt_rateest_free_rcu);
> }
> mutex_unlock(&xt_rateest_mutex);
> }
> @@ -179,6 +188,7 @@ static int __init xt_rateest_tg_init(void)
> static void __exit xt_rateest_tg_fini(void)
> {
> xt_unregister_target(&xt_rateest_tg_reg);
> + rcu_barrier(); /* Wait for completion of call_rcu()'s (xt_rateest_free_rcu) */
> }
>
>
> diff --git a/net/sched/act_api.c b/net/sched/act_api.c
> index 972378f..23b25f8 100644
> --- a/net/sched/act_api.c
> +++ b/net/sched/act_api.c
> @@ -26,6 +26,11 @@
> #include <net/act_api.h>
> #include <net/netlink.h>
>
> +static void tcf_common_free_rcu(struct rcu_head *head)
> +{
> + kfree(container_of(head, struct tcf_common, tcfc_rcu));
> +}
> +
> void tcf_hash_destroy(struct tcf_common *p, struct tcf_hashinfo *hinfo)
> {
> unsigned int h = tcf_hash(p->tcfc_index, hinfo->hmask);
> @@ -38,7 +43,11 @@ void tcf_hash_destroy(struct tcf_common *p, struct tcf_hashinfo *hinfo)
> write_unlock_bh(hinfo->lock);
> gen_kill_estimator(&p->tcfc_bstats,
> &p->tcfc_rate_est);
> - kfree(p);
> + /*
> + * gen_estimator est_timer() might access p->tcfc_lock
> + * or bstats, wait a RCU grace period before freeing p
> + */
> + call_rcu(&p->tcfc_rcu, tcf_common_free_rcu);
> return;
> }
> }
> diff --git a/net/sched/act_police.c b/net/sched/act_police.c
> index 654f73d..537a487 100644
> --- a/net/sched/act_police.c
> +++ b/net/sched/act_police.c
> @@ -97,6 +97,11 @@ nla_put_failure:
> goto done;
> }
>
> +static void tcf_police_free_rcu(struct rcu_head *head)
> +{
> + kfree(container_of(head, struct tcf_police, tcf_rcu));
> +}
> +
> static void tcf_police_destroy(struct tcf_police *p)
> {
> unsigned int h = tcf_hash(p->tcf_index, POL_TAB_MASK);
> @@ -113,7 +118,11 @@ static void tcf_police_destroy(struct tcf_police *p)
> qdisc_put_rtab(p->tcfp_R_tab);
> if (p->tcfp_P_tab)
> qdisc_put_rtab(p->tcfp_P_tab);
> - kfree(p);
> + /*
> + * gen_estimator est_timer() might access p->tcf_lock
> + * or bstats, wait a RCU grace period before freeing p
> + */
> + call_rcu(&p->tcf_rcu, tcf_police_free_rcu);
> return;
> }
> }
> @@ -397,6 +406,7 @@ static void __exit
> police_cleanup_module(void)
> {
> tcf_unregister_action(&act_police_ops);
> + rcu_barrier(); /* Wait for completion of call_rcu()'s (tcf_police_free_rcu) */
> }
>
> module_init(police_init_module);
>
>
--
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