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

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Date:   Mon, 14 May 2018 18:23:01 +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 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?

> 	p = idr_find(&idrinfo->action_idr, index);
>+	if (p) {
>+		refcount_inc(&p->tcfa_refcnt);
>+		if (bind)
>+			atomic_inc(&p->tcfa_bindcnt);
>+	}
> 	spin_unlock_bh(&idrinfo->lock);

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