linux-kernel - Re: [PATCH 05/14] net: sched: always take reference to action

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Date:   Tue, 15 May 2018 10:58:27 +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 05/14] net: sched: always take reference to action

Mon, May 14, 2018 at 08:49:07PM CEST, vladbu@...lanox.com wrote:
>
>On Mon 14 May 2018 at 16:23, Jiri Pirko <jiri@...nulli.us> wrote:
>> Mon, May 14, 2018 at 04:27:06PM CEST, vladbu@...lanox.com wrote:
>>>Without rtnl lock protection it is no longer safe to use pointer to tc
>>>action without holding reference to it. (it can be destroyed concurrently)
>>>
>>>Remove unsafe action idr lookup function. Instead of it, implement safe tcf
>>>idr check function that atomically looks up action in idr and increments
>>>its reference and bind counters.
>>>
>>>Implement both action search and check using new safe function.
>>>
>>>Signed-off-by: Vlad Buslov <vladbu@...lanox.com>
>>>---
>>> net/sched/act_api.c | 38 ++++++++++++++++----------------------
>>> 1 file changed, 16 insertions(+), 22 deletions(-)
>>>
>>>diff --git a/net/sched/act_api.c b/net/sched/act_api.c
>>>index 1331beb..9459cce 100644
>>>--- a/net/sched/act_api.c
>>>+++ b/net/sched/act_api.c
>>>@@ -284,44 +284,38 @@ int tcf_generic_walker(struct tc_action_net *tn, struct sk_buff *skb,
>>> }
>>> EXPORT_SYMBOL(tcf_generic_walker);
>>> 
>>>-static struct tc_action *tcf_idr_lookup(u32 index, struct tcf_idrinfo *idrinfo)
>>>+bool __tcf_idr_check(struct tc_action_net *tn, u32 index, struct tc_action **a,
>>>+		     int bind)
>>> {
>>>-	struct tc_action *p = NULL;
>>>+	struct tcf_idrinfo *idrinfo = tn->idrinfo;
>>>+	struct tc_action *p;
>>> 
>>> 	spin_lock_bh(&idrinfo->lock);
>>
>> Why "_bh" variant is necessary here?
>
>It is not my code.

Yeah, yet still I wonder :)