netdev - Re: [PATCH] net: net_cls: remove a NULL check for css_cls

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Date:   Wed, 25 Apr 2018 16:35:02 +0800
From:   Li RongQing <roy.qing.li@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     lirongqing@...du.com, netdev@...r.kernel.org
Subject: Re: [PATCH] net: net_cls: remove a NULL check for css_cls_state

On 4/20/18, David Miller <davem@...emloft.net> wrote:
> From: Li RongQing <lirongqing@...du.com>
> Date: Thu, 19 Apr 2018 12:59:21 +0800
>
>> The input of css_cls_state() is impossible to NULL except
>> cgrp_css_online, so simplify it
>>
>> Signed-off-by: Li RongQing <lirongqing@...du.com>
>
> I don't view this as an improvement.  Just let the helper always check
> NULL and that way there are less situations to audit.
>
css_cls_state maybe return NULL, but nearly no places check the return
value with NULL, this seems unreadable.

net/core/netclassid_cgroup.c:27:        return
css_cls_state(task_css_check(p, net_cls_cgrp_id,
net/core/netclassid_cgroup.c:46:        struct cgroup_cls_state *cs =
css_cls_state(css);
net/core/netclassid_cgroup.c:47:        struct cgroup_cls_state
*parent = css_cls_state(css->parent);
net/core/netclassid_cgroup.c:57:        kfree(css_cls_state(css));
net/core/netclassid_cgroup.c:82:                           (void
*)(unsigned long)css_cls_state(css)->classid);
net/core/netclassid_cgroup.c:89:        return css_cls_state(css)->classid;
net/core/netclassid_cgroup.c:95:        struct cgroup_cls_state *cs =
css_cls_state(css);

> And it's not like this is a critical fast path either.
>

I see css_cls_state will be called  when send packet if
CONFIG_NET_CLS_ACT and CONFIG_NET_EGRESS enabled, the calling stack is
like below:

css_cls_state
  task_cls_state
    task_get_classid
       cls_cgroup_classify
          tcf_classify
            sch_handle_egress
               __dev_queue_xmit
                        CONFIG_NET_CLS_ACT
                         CONFIG_NET_EGRESS

-RongQing






> I'm not applying this, sorry.
>