netdev - Re: [Patch net] kcm: fix a race condition in kcm

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Message-ID: <Y1wrp4pL4BmUL0LE@pop-os.localdomain>
Date:   Fri, 28 Oct 2022 12:21:11 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, Cong Wang <cong.wang@...edance.com>,
        shaozhengchao <shaozhengchao@...wei.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Tom Herbert <tom@...bertland.com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [Patch net] kcm: fix a race condition in kcm_recvmsg()

On Tue, Oct 25, 2022 at 04:02:22PM -0700, Jakub Kicinski wrote:
> On Sat, 22 Oct 2022 19:30:44 -0700 Cong Wang wrote:
> > +			spin_lock_bh(&mux->rx_lock);
> >  			KCM_STATS_INCR(kcm->stats.rx_msgs);
> >  			skb_unlink(skb, &sk->sk_receive_queue);
> > +			spin_unlock_bh(&mux->rx_lock);
> 
> Why not switch to __skb_unlink() at the same time?
> Abundance of caution?

What gain do we have? Since we have rx_lock, skb queue lock should never
be contended?

Thanks.