linux-kernel - Re: [PATCH 07/14] net: sched: use reference counting action init

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Message-ID: <vbflgclm9wc.fsf@reg-r-vrt-018-180.mtr.labs.mlnx>
Date:   Tue, 15 May 2018 14:32:51 +0300
From:   Vlad Buslov <vladbu@...lanox.com>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, jhs@...atatu.com,
        xiyou.wangcong@...il.com, pablo@...filter.org,
        kadlec@...ckhole.kfki.hu, fw@...len.de, ast@...nel.org,
        daniel@...earbox.net, edumazet@...gle.com, keescook@...omium.org,
        linux-kernel@...r.kernel.org, netfilter-devel@...r.kernel.org,
        coreteam@...filter.org, kliteyn@...lanox.com
Subject: Re: [PATCH 07/14] net: sched: use reference counting action init


On Tue 15 May 2018 at 11:24, Jiri Pirko <jiri@...nulli.us> wrote:
> Mon, May 14, 2018 at 04:27:08PM CEST, vladbu@...lanox.com wrote:
>>Change action API to assume that action init function always takes
>>reference to action, even when overwriting existing action. This is
>>necessary because action API continues to use action pointer after init
>>function is done. At this point action becomes accessible for concurrent
>>modifications so user must always hold reference to it.
>>
>>Implement helper put list function to atomically release list of actions
>>after action API init code is done using them.
>>
>>Signed-off-by: Vlad Buslov <vladbu@...lanox.com>
>>---
>> net/sched/act_api.c | 38 +++++++++++++++++---------------------
>> 1 file changed, 17 insertions(+), 21 deletions(-)
>>
>
> [...]
>
>
>>@@ -1196,8 +1190,7 @@ tca_action_gd(struct net *net, struct nlattr *nla, struct nlmsghdr *n,
>> 		return ret;
>> 	}
>> err:
>>-	if (event != RTM_GETACTION)
>
> Howcome you do this for RTM_GETACTION now too? Where is the related
> "get"?

In patch 5. There is always a possibility of concurrent delete without
rtnl lock so all usages of action pointers were converted to hold
reference to action.

>
>
>>-		tcf_action_destroy(&actions, 0);
>>+	tcf_action_put_lst(&actions);
>> 	return ret;
>> }
>> 
>
> [...]