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Date:   Tue, 15 Feb 2022 11:47:01 -0700
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Subject: Re: [PATCH net-next 01/19] net: tcp: introduce tcp_drop_reason()
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To:     Eric Dumazet <edumazet@google.com>,
        Menglong Dong <menglong8.dong@gmail.com>
Cc:     Jakub Kicinski <kuba@kernel.org>,
        David Miller <davem@davemloft.net>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Jesper Dangaard Brouer <hawk@kernel.org>,
        John Fastabend <john.fastabend@gmail.com>,
        Menglong Dong <imagedong@tencent.com>,
        Talal Ahmad <talalahmad@google.com>,
        Kees Cook <keescook@chromium.org>,
        Ilias Apalodimas <ilias.apalodimas@linaro.org>,
        Alexander Lobakin <alobakin@pm.me>,
        Kumar Kartikeya Dwivedi <memxor@gmail.com>,
        Antoine Tenart <atenart@kernel.org>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Paolo Abeni <pabeni@redhat.com>,
        Yunsheng Lin <linyunsheng@huawei.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Yajun Deng <yajun.deng@linux.dev>,
        Roopa Prabhu <roopa@nvidia.com>,
        Willem de Bruijn <willemb@google.com>,
        Vasily Averin <vvs@virtuozzo.com>,
        Cong Wang <cong.wang@bytedance.com>,
        Luiz Augusto von Dentz <luiz.von.dentz@intel.com>,
        LKML <linux-kernel@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
        flyingpeng@tencent.com
References: <20220215112812.2093852-1-imagedong@tencent.com>
 <20220215112812.2093852-2-imagedong@tencent.com>
 <CANn89iLWOBy=X1CpY+gvukhQ-bb7hDWd5y+m46K7o5XR0Pbt_A@mail.gmail.com>
From:   David Ahern <dsahern@kernel.org>
In-Reply-To: <CANn89iLWOBy=X1CpY+gvukhQ-bb7hDWd5y+m46K7o5XR0Pbt_A@mail.gmail.com>
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On 2/15/22 10:34 AM, Eric Dumazet wrote:
>> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
>> index af94a6d22a9d..e3811afd1756 100644
>> --- a/net/ipv4/tcp_input.c
>> +++ b/net/ipv4/tcp_input.c
>> @@ -4684,10 +4684,19 @@ static bool tcp_ooo_try_coalesce(struct sock *sk,
>>         return res;
>>  }
>>
>> -static void tcp_drop(struct sock *sk, struct sk_buff *skb)
>> +static void tcp_drop_reason(struct sock *sk, struct sk_buff *skb,
>> +                           enum skb_drop_reason reason)
>>  {
>>         sk_drops_add(sk, skb);
>> -       __kfree_skb(skb);
>> +       /* why __kfree_skb() used here before, other than kfree_skb()?
>> +        * confusing......
> 
> Do not add comments like that if you do not know the difference...
> 
> __kfree_skb() is used by TCP stack because it owns skb in receive
> queues, and avoids touching skb->users
> because it must be one already.

and it bypasses kfree_skb tracepoint which seems by design.