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Date: Wed, 16 Feb 2022 10:38:28 +0800 From: Menglong Dong <menglong8.dong@...il.com> To: David Ahern <dsahern@...nel.org> Cc: Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, David Miller <davem@...emloft.net>, Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...hat.com>, Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Jesper Dangaard Brouer <hawk@...nel.org>, John Fastabend <john.fastabend@...il.com>, Menglong Dong <imagedong@...cent.com>, Talal Ahmad <talalahmad@...gle.com>, Kees Cook <keescook@...omium.org>, Ilias Apalodimas <ilias.apalodimas@...aro.org>, Alexander Lobakin <alobakin@...me>, Kumar Kartikeya Dwivedi <memxor@...il.com>, Antoine Tenart <atenart@...nel.org>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Paolo Abeni <pabeni@...hat.com>, Yunsheng Lin <linyunsheng@...wei.com>, Arnd Bergmann <arnd@...db.de>, Yajun Deng <yajun.deng@...ux.dev>, Roopa Prabhu <roopa@...dia.com>, Willem de Bruijn <willemb@...gle.com>, Vasily Averin <vvs@...tuozzo.com>, Cong Wang <cong.wang@...edance.com>, Luiz Augusto von Dentz <luiz.von.dentz@...el.com>, LKML <linux-kernel@...r.kernel.org>, netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>, flyingpeng@...cent.com Subject: Re: [PATCH net-next 01/19] net: tcp: introduce tcp_drop_reason() On Wed, Feb 16, 2022 at 2:47 AM David Ahern <dsahern@...nel.org> wrote: > > 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. Do you mean it shouldn't be traced here? According to my understanding, __kfree_skb() was used in the beginning as skb->users aren't touched by TCP. Later, tcp_drop() was introduced to record drop count to the socket. Considering the skb is indeed dropped and no other event is triggered, is it ok to trigger the kfree_skb tracepoint? Thanks! Menglong Dong
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