On Wed, Feb 16, 2022 at 1:34 AM Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
>
> On Tue, Feb 15, 2022 at 3:30 AM <menglong8.dong@xxxxxxxxx> wrote:
> >
> > From: Menglong Dong <imagedong@xxxxxxxxxxx>
> >
> > For TCP protocol, tcp_drop() is used to free the skb when it needs
> > to be dropped. To make use of kfree_skb_reason() and collect drop
> > reasons, introduce the function tcp_drop_reason().
> >
> > tcp_drop_reason() will finally call kfree_skb_reason() and pass the
> > drop reason to 'kfree_skb' tracepoint.
> >
> > PS: __kfree_skb() was used in tcp_drop(), I'm not sure if it's ok
> > to replace it with kfree_skb_reason().
> >
> > Signed-off-by: Menglong Dong <imagedong@xxxxxxxxxxx>
> > ---
> > net/ipv4/tcp_input.c | 13 +++++++++++--
> > 1 file changed, 11 insertions(+), 2 deletions(-)
> >
> > 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.
>
> (We made sure not using skb_get() in TCP)
>
> It seems fine to use kfree_skb() in tcp_drop(), it is hardly fast
> path, and the added cost is pure noise.
I understand why __kfree_skb() was used now, and it seems
this commit is ok (with the comments removed of course). I'll
keep it still.
Thanks!
Menglong Dong
