netdev - Re: [PATCH] af_unix: fix holding spinlock in oob handling

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Date:   Thu, 12 Aug 2021 13:38:39 -0700
From:   Shoaib Rao <rao.shoaib@...cle.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     netdev <netdev@...r.kernel.org>, Jakub Kicinski <kuba@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH] af_unix: fix holding spinlock in oob handling


On 8/12/21 1:33 PM, Eric Dumazet wrote:
> On Thu, Aug 12, 2021 at 7:37 PM Shoaib Rao <rao.shoaib@...cle.com> wrote:
>>
>> On 8/12/21 12:53 AM, Eric Dumazet wrote:
>>>           if (ousk->oob_skb)
>>> -               kfree_skb(ousk->oob_skb);
>>> +               consume_skb(ousk->oob_skb);
>> Should I be using consume_skb(), as the skb is not being consumed, the
>> ref count is decremented and if zero skb will be freed.
>>
> consume_skb() and kfree_skb() have the same ref count handling.
>
> The difference is that kfree_skb() is used by convention when a packet
> is dropped
>
> Admins can look closely at packet drops with drop_monitor, or :
>
> perf record -a -g -e skb:kfree_skb sleep 10
> perf report
>
> In your case, the oob_skb is not really dropped. It is replaced by
> another one, it is part of the normal operation.

Thanks a lot for the explanation. This was very helpful. In my case the 
skb may be dropped (oob was not read but the read has passed beyond oob, 
or could become part of normal data). Anyways, I will change it to use 
consume_skb().

Regards,

Shoaib