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

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Date:   Tue, 15 May 2018 15:00:28 +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 11:57, Jiri Pirko <jiri@...nulli.us> wrote:
> Tue, May 15, 2018 at 01:41:45PM CEST, vladbu@...lanox.com wrote:
>>
>>On Tue 15 May 2018 at 11:39, Jiri Pirko <jiri@...nulli.us> wrote:
>>> Tue, May 15, 2018 at 01:32:51PM CEST, vladbu@...lanox.com wrote:
>>>>
>>>>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.
>>>
>>> So that means that if you run kernel in between, with patch 5 but
>>> without patch 7 and you do RTM_GETACTION, you leak a reference, right?
>>
>>Right.
>
> That is an issue. You need to make sure that the code is without bugs
> like this after every applied patch. You need to make sure the code is
> bisectable.

Got it. Will fix in V2.

>
> Thanks.