netdev - Re: [PATCH net-next] net: sched: ingress: set 'unlocked' flag for Qdisc ops

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Message-ID: <72a3e9e9-e417-d46a-e0b2-b7e684c60b47@iogearbox.net>
Date:   Thu, 13 Jun 2019 10:27:32 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Vlad Buslov <vladbu@...lanox.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "jhs@...atatu.com" <jhs@...atatu.com>,
        "xiyou.wangcong@...il.com" <xiyou.wangcong@...il.com>,
        "jiri@...nulli.us" <jiri@...nulli.us>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "alexei.starovoitov@...il.com" <alexei.starovoitov@...il.com>
Subject: Re: [PATCH net-next] net: sched: ingress: set 'unlocked' flag for
 Qdisc ops

On 06/13/2019 09:06 AM, Vlad Buslov wrote:
> On Wed 12 Jun 2019 at 19:33, Daniel Borkmann <daniel@...earbox.net> wrote:
>> On 06/12/2019 09:14 AM, Vlad Buslov wrote:
>>> To remove rtnl lock dependency in tc filter update API when using ingress
>>> Qdisc, set QDISC_CLASS_OPS_DOIT_UNLOCKED flag in ingress Qdisc_class_ops.
>>>
>>> Ingress Qdisc ops don't require any modifications to be used without rtnl
>>> lock on tc filter update path. Ingress implementation never changes its
>>> q->block and only releases it when Qdisc is being destroyed. This means it
>>> is enough for RTM_{NEWTFILTER|DELTFILTER|GETTFILTER} message handlers to
>>> hold ingress Qdisc reference while using it without relying on rtnl lock
>>> protection. Unlocked Qdisc ops support is already implemented in filter
>>> update path by unlocked cls API patch set.
>>>
>>> Signed-off-by: Vlad Buslov <vladbu@...lanox.com>
>>> ---
>>>  net/sched/sch_ingress.c | 1 +
>>>  1 file changed, 1 insertion(+)
>>>
>>> diff --git a/net/sched/sch_ingress.c b/net/sched/sch_ingress.c
>>> index 0f65f617756b..d5382554e281 100644
>>> --- a/net/sched/sch_ingress.c
>>> +++ b/net/sched/sch_ingress.c
>>> @@ -114,6 +114,7 @@ static int ingress_dump(struct Qdisc *sch, struct sk_buff *skb)
>>>  }
>>>
>>>  static const struct Qdisc_class_ops ingress_class_ops = {
>>> +	.flags		=	QDISC_CLASS_OPS_DOIT_UNLOCKED,
>>>  	.leaf		=	ingress_leaf,
>>>  	.find		=	ingress_find,
>>>  	.walk		=	ingress_walk,
>>>
>>
>> Vlad, why is clsact_class_ops not updated here? Please elaborate!
> 
> Daniel, no particular reason to not enable unlocked execution for
> clsact. I set the unlocked flag for ingress because that was the Qdisc
> that I tested all my parallel tc changes on. However, ingress and clsact
> implementations are quite similar, so I can send a followup patch that
> updates clsact_class_ops, if you want.

Yes, please do, they are pretty much the same except that clsact supersedes
ingress in that it also offers an egress hook.