From: Stefano Brivio <sbrivio@redhat.com>
To: Vlad Buslov <vladbu@mellanox.com>
Cc: "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"jhs@mojatatu.com" <jhs@mojatatu.com>,
"xiyou.wangcong@gmail.com" <xiyou.wangcong@gmail.com>,
"jiri@resnulli.us" <jiri@resnulli.us>,
"davem@davemloft.net" <davem@davemloft.net>
Subject: Re: [PATCH net-next 03/12] net: sched: flower: introduce reference counting for filters
Date: Fri, 15 Feb 2019 13:32:10 +0100 [thread overview]
Message-ID: <20190215133210.64a99e93@redhat.com> (raw)
In-Reply-To: <vbfef89jny6.fsf@mellanox.com>
On Fri, 15 Feb 2019 11:22:45 +0000
Vlad Buslov <vladbu@mellanox.com> wrote:
> On Thu 14 Feb 2019 at 20:34, Stefano Brivio <sbrivio@redhat.com> wrote:
> > On Thu, 14 Feb 2019 09:47:03 +0200
> > Vlad Buslov <vladbu@mellanox.com> wrote:
> >
> >> +static struct cls_fl_filter *fl_get_next_filter(struct tcf_proto *tp,
> >> + unsigned long *handle)
> >> +{
> >> + struct cls_fl_head *head = fl_head_dereference(tp);
> >> + struct cls_fl_filter *f;
> >> +
> >> + rcu_read_lock();
> >> + /* don't return filters that are being deleted */
> >> + while ((f = idr_get_next_ul(&head->handle_idr,
> >> + handle)) != NULL &&
> >> + !refcount_inc_not_zero(&f->refcnt))
> >> + ++(*handle);
> >
> > This... hurts :) What about:
> >
> > while ((f = idr_get_next_ul(&head->handle_idr, &handle))) {
> > if (refcount_inc_not_zero(&f->refcnt))
> > break;
> > ++(*handle);
> > }
> >
> > ?
>
> I prefer to avoid using value of assignment as boolean and
> non-structured jumps, when possible. In this case it seems OK either
> way, but how about:
>
> for (f = idr_get_next_ul(&head->handle_idr, handle);
> f && !refcount_inc_not_zero(&f->refcnt);
> f = idr_get_next_ul(&head->handle_idr, handle))
> ++(*handle);
Honestly, I preferred the original, this is repeating idr_get_next_ul()
twice.
Maybe, just:
[...]
struct idr *idr;
[...]
idr = &head->handle_idr;
while ((f = idr_get_next_ul(idr, handle)) != NULL &&
!refcount_inc_not_zero(&f->refcnt))
++(*handle);
also rather ugly, but not entirely unreadable. I tried drafting a
helper for this, but it just ends up hiding what this does.
> >> @@ -1349,6 +1404,7 @@ static int fl_change(struct net *net, struct sk_buff *in_skb,
> >> err = -ENOBUFS;
> >> goto errout_tb;
> >> }
> >> + refcount_set(&fnew->refcnt, 1);
> >>
> >> err = tcf_exts_init(&fnew->exts, TCA_FLOWER_ACT, 0);
> >> if (err < 0)
> >> @@ -1381,6 +1437,7 @@ static int fl_change(struct net *net, struct sk_buff *in_skb,
> >> if (!tc_in_hw(fnew->flags))
> >> fnew->flags |= TCA_CLS_FLAGS_NOT_IN_HW;
> >>
> >> + refcount_inc(&fnew->refcnt);
> >
> > I guess I'm not getting the semantics but... why is it 2 now?
>
> As soon as fnew is inserted into head->handle_idr (one reference), it
> becomes accessible to concurrent users, which means that it can be
> deleted at any time. However, tp->change() returns a reference to newly
> created filter to cls_api by assigning "arg" parameter to it (second
> reference). After tp->change() returns, cls API continues to use fnew
> and releases it with tfilter_put() when finished.
I see, thanks for the explanation!
--
Stefano
next prev parent reply other threads:[~2019-02-15 12:32 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-14 7:47 [PATCH net-next 00/12] Refactor flower classifier to remove dependency on rtnl lock Vlad Buslov
2019-02-14 7:47 ` [PATCH net-next 01/12] net: sched: flower: don't check for rtnl on head dereference Vlad Buslov
2019-02-18 19:08 ` Cong Wang
2019-02-19 9:45 ` Vlad Buslov
2019-02-20 22:33 ` Cong Wang
2019-02-21 17:45 ` Vlad Buslov
2019-02-22 19:32 ` Cong Wang
2019-02-25 16:11 ` Vlad Buslov
2019-02-25 22:39 ` Cong Wang
2019-02-26 14:57 ` Vlad Buslov
2019-02-28 0:49 ` Cong Wang
2019-02-28 18:35 ` Vlad Buslov
2019-03-02 0:51 ` Cong Wang
2019-02-14 7:47 ` [PATCH net-next 02/12] net: sched: flower: refactor fl_change Vlad Buslov
2019-02-14 20:34 ` Stefano Brivio
2019-02-15 10:38 ` Vlad Buslov
2019-02-15 10:47 ` Stefano Brivio
2019-02-15 16:25 ` Vlad Buslov
2019-02-18 18:20 ` Stefano Brivio
2019-02-14 7:47 ` [PATCH net-next 03/12] net: sched: flower: introduce reference counting for filters Vlad Buslov
2019-02-14 20:34 ` Stefano Brivio
2019-02-15 11:22 ` Vlad Buslov
2019-02-15 12:32 ` Stefano Brivio [this message]
2019-02-14 7:47 ` [PATCH net-next 04/12] net: sched: flower: track filter deletion with flag Vlad Buslov
2019-02-14 20:49 ` Stefano Brivio
2019-02-15 15:54 ` Vlad Buslov
2019-02-14 7:47 ` [PATCH net-next 05/12] net: sched: flower: add reference counter to flower mask Vlad Buslov
2019-02-14 7:47 ` [PATCH net-next 06/12] net: sched: flower: handle concurrent mask insertion Vlad Buslov
2019-02-15 22:46 ` Stefano Brivio
2019-02-14 7:47 ` [PATCH net-next 07/12] net: sched: flower: protect masks list with spinlock Vlad Buslov
2019-02-14 7:47 ` [PATCH net-next 08/12] net: sched: flower: handle concurrent filter insertion in fl_change Vlad Buslov
2019-02-14 7:47 ` [PATCH net-next 09/12] net: sched: flower: handle concurrent tcf proto deletion Vlad Buslov
2019-02-18 20:47 ` Cong Wang
2019-02-19 14:08 ` Vlad Buslov
2019-02-14 7:47 ` [PATCH net-next 10/12] net: sched: flower: protect flower classifier state with spinlock Vlad Buslov
2019-02-14 7:47 ` [PATCH net-next 11/12] net: sched: flower: track rtnl lock state Vlad Buslov
2019-02-15 22:46 ` Stefano Brivio
2019-02-18 9:35 ` Vlad Buslov
2019-02-14 7:47 ` [PATCH net-next 12/12] net: sched: flower: set unlocked flag for flower proto ops Vlad Buslov
2019-02-18 19:27 ` Cong Wang
2019-02-19 10:15 ` Vlad Buslov
2019-02-20 22:36 ` Cong Wang
2019-02-18 19:15 ` [PATCH net-next 00/12] Refactor flower classifier to remove dependency on rtnl lock Cong Wang
2019-02-19 10:00 ` Vlad Buslov
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