netdev - Re: [PATCH net-next 3/3] net/sched: act_pedit: rate limit datapath messages

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Message-ID: <dbdb0bf7-2bc6-4002-d7f2-e561d6120856@mojatatu.com>
Date:   Mon, 13 Mar 2023 15:24:47 -0300
From:   Pedro Tammela <pctammela@...atatu.com>
To:     Simon Horman <simon.horman@...igine.com>
Cc:     netdev@...r.kernel.org, jhs@...atatu.com, xiyou.wangcong@...il.com,
        jiri@...nulli.us, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com
Subject: Re: [PATCH net-next 3/3] net/sched: act_pedit: rate limit datapath
 messages

On 10/03/2023 11:21, Simon Horman wrote:
> On Thu, Mar 09, 2023 at 03:51:58PM -0300, Pedro Tammela wrote:
>> Unbounded info messages in the pedit datapath can flood the printk ring buffer quite easily
>> depending on the action created. As these messages are informational, usually printing
>> some, not all, is enough to bring attention to the real issue.
> 
> Would this reasoning also apply to other TC actions?

Hi Simon,

So far, the only action that has datapath pr_info() messages is pedit.
This seems like it comes from the old days, according to git.

> 
>> Reviewed-by: Jamal Hadi Salim <jhs@...atatu.com>
>> Signed-off-by: Pedro Tammela <pctammela@...atatu.com>
>> ---
>>   net/sched/act_pedit.c | 17 +++++++----------
>>   1 file changed, 7 insertions(+), 10 deletions(-)
>>
>> diff --git a/net/sched/act_pedit.c b/net/sched/act_pedit.c
>> index e42cbfc369ff..b5a8fc19ee55 100644
>> --- a/net/sched/act_pedit.c
>> +++ b/net/sched/act_pedit.c
>> @@ -388,9 +388,8 @@ TC_INDIRECT_SCOPE int tcf_pedit_act(struct sk_buff *skb,
>>   		}
>>   
>>   		rc = pedit_skb_hdr_offset(skb, htype, &hoffset);
>> -		if (rc) {
>> -			pr_info("tc action pedit bad header type specified (0x%x)\n",
>> -				htype);
>> +		if (unlikely(rc)) {
> 
> Do you really need unlikely() here (and no where else?)

This case in particular is already checked in the netlink parsing code 
on create/update.
I was gonna delete the condition initially but then thought of hiding it 
under an unlikely branch.
As for the other branches, I didn't see much of a reason.

> 
>> +			pr_info_ratelimited("tc action pedit bad header type specified (0x%x)\n", htype);
>>   			goto bad;
>>   		}
>>   
> 
> ...