netdev - Re: [PATCH net 1/1] net sched actions: fix GETing actions

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Date:   Thu, 8 Sep 2016 10:12:20 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>
Cc:     David Miller <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH net 1/1] net sched actions: fix GETing actions

On Thu, Sep 8, 2016 at 5:12 AM, Jamal Hadi Salim <jhs@...atatu.com> wrote:
> From: Jamal Hadi Salim <jhs@...atatu.com>
>
> Example of what broke:
> ...add a gact action to drop
> sudo $TC actions add action drop index 10
> ...now retrieve it, looks good
> sudo $TC actions get action gact index 10
> ...retrieve it again and find it is gone!
> sudo $TC actions get action gact index 10

This changelog sucks, it only tells the phenomenon of the bug,
never explains what causes the bug, which is crucial for review.

>
> Fixes: f07fed82ad79 ("net_sched: remove the leftover cleanup_a())
>
> Signed-off-by: Jamal Hadi Salim <jhs@...atatu.com>
> ---
>  net/sched/act_api.c | 20 +++++++++++++++++---
>  1 file changed, 17 insertions(+), 3 deletions(-)
>
> diff --git a/net/sched/act_api.c b/net/sched/act_api.c
> index d09d068..d4b4704 100644
> --- a/net/sched/act_api.c
> +++ b/net/sched/act_api.c
> @@ -612,6 +612,8 @@ int tcf_action_init(struct net *net, struct nlattr *nla,
>                         goto err;
>                 }
>                 act->order = i;
> +               if (ovr)
> +                       act->tcfa_refcnt+=1;

This looks like not relevant to commit f07fed82ad79 at all?


>                 list_add_tail(&act->list, actions);
>         }
>         return 0;
> @@ -856,6 +858,15 @@ tcf_del_notify(struct net *net, struct nlmsghdr *n, struct list_head *actions,
>         return ret;
>  }
>
> +static void cleanup_a(struct list_head *actions)
> +{
> +       struct tc_action *a, *tmp;
> +
> +       list_for_each_entry_safe(a, tmp, actions, list) {
> +               list_del(&a->list);
> +       }

After my patches, all the action lists are now temporary,
you didn't explain why we should remove an action from
a temporary list, they should just come and go, since
we call ist_add() every time.

Did see any list corruption or kernel crash (your changelog
didn't say so)?


> +}
> +
>  static int
>  tca_action_gd(struct net *net, struct nlattr *nla, struct nlmsghdr *n,
>               u32 portid, int event)
> @@ -883,6 +894,7 @@ tca_action_gd(struct net *net, struct nlattr *nla, struct nlmsghdr *n,
>                         goto err;
>                 }
>                 act->order = i;
> +               act->tcfa_refcnt+=1;


Maybe we only need to fixup the refcnt without touching list,
from my quick observation to your bug report (again, you didn't explain).


>                 list_add_tail(&act->list, &actions);
>         }
>
> @@ -892,10 +904,12 @@ tca_action_gd(struct net *net, struct nlattr *nla, struct nlmsghdr *n,
>                 ret = tcf_del_notify(net, n, &actions, portid);
>                 if (ret)
>                         goto err;
> +               cleanup_a(&actions);
>                 return ret;
>         }
>  err:
>         tcf_action_destroy(&actions, 0);
> +       cleanup_a(&actions);
>         return ret;
>  }
>
> @@ -931,10 +945,10 @@ tcf_action_add(struct net *net, struct nlattr *nla, struct nlmsghdr *n,
>         LIST_HEAD(actions);
>
>         ret = tcf_action_init(net, nla, NULL, NULL, ovr, 0, &actions);
> -       if (ret)
> -               return ret;
>
> -       return tcf_add_notify(net, n, &actions, portid);
> +       ret = tcf_add_notify(net, n, &actions, portid);
> +       cleanup_a(&actions);
> +       return ret;
>  }
>
>  static int tc_ctl_action(struct sk_buff *skb, struct nlmsghdr *n)
> --
> 1.9.1
>