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

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Message-ID: <CANn89iKx9JW8atr96MJHpU34C7c3Wm72cbxkxUJQmoj=mX2UoQ@mail.gmail.com>
Date:   Thu, 12 Aug 2021 22:33:30 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Shoaib Rao <rao.shoaib@...cle.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 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.