Re: [PATCH net-next] net_sched: make qdisc_reset() smaller

From: Eric Dumazet <edumazet@google.com>
To: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>,
	"David S . Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Jamal Hadi Salim <jhs@mojatatu.com>,
	Jiri Pirko <jiri@resnulli.us>, netdev <netdev@vger.kernel.org>
Subject: Re: [PATCH net-next] net_sched: make qdisc_reset() smaller
Date: Sun, 17 Apr 2022 15:41:40 -0700	[thread overview]
Message-ID: <CANn89iLrk_iQ8MJTLcueijnmowkuJEVSO_kBmm7y8Z--AGpz4g@mail.gmail.com> (raw)
In-Reply-To: <CAM_iQpXb=-hdGbdbpTbDBGJKyYPhn3SxXUUowHg5gTy20W=iiQ@mail.gmail.com>

On Sun, Apr 17, 2022 at 3:30 PM Cong Wang <xiyou.wangcong@gmail.com> wrote:
>
> On Wed, Apr 13, 2022 at 6:11 PM Eric Dumazet <eric.dumazet@gmail.com> wrote:
> >
> > From: Eric Dumazet <edumazet@google.com>
> >
> > For some unknown reason qdisc_reset() is using
> > a convoluted way of freeing two lists of skbs.
> >
> > Use __skb_queue_purge() instead.
> [...]
> >
> > -       skb_queue_walk_safe(&qdisc->gso_skb, skb, tmp) {
> > -               __skb_unlink(skb, &qdisc->gso_skb);
> > -               kfree_skb_list(skb);
>
> Isn't it precisely because of this kfree_skb_list()?

Note the __skb_unlink(skb, &qdisc->gso_skb) which happens at the line above.

__skb_unlink(...)
{
...
skb->next  = skb->prev = NULL;
...
}

This means skb->next is NULL, thus there is no list of skb attached to @skb ?

kfree_skb_list(skb) is thus a convoluted way to call kfree_skb(skb)

It seems to me that this construct had been copy/pasted from elsewhere.