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

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Date:   Tue, 15 May 2018 13:39:54 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Vlad Buslov <vladbu@...lanox.com>
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

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?


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