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Date:   Wed, 17 May 2023 11:48:25 -0700
From:   Jakub Kicinski <kuba@kernel.org>
To:     Peilin Ye <yepeilin.cs@gmail.com>
Cc:     "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Paolo Abeni <pabeni@redhat.com>,
        Jamal Hadi Salim <jhs@mojatatu.com>,
        Cong Wang <xiyou.wangcong@gmail.com>,
        Jiri Pirko <jiri@resnulli.us>,
        Peilin Ye <peilin.ye@bytedance.com>,
        Daniel Borkmann <daniel@iogearbox.net>,
        John Fastabend <john.r.fastabend@intel.com>,
        Vlad Buslov <vladbu@mellanox.com>,
        Pedro Tammela <pctammela@mojatatu.com>,
        Hillf Danton <hdanton@sina.com>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, Cong Wang <cong.wang@bytedance.com>
Subject: Re: [PATCH net 6/6] net/sched: qdisc_destroy() old ingress and
 clsact Qdiscs before grafting
Message-ID: <20230517114825.5d7c85a4@kernel.org>
In-Reply-To: <e6c4681dd9205d702ae2e6124e20c6210520e76e.1683326865.git.peilin.ye@bytedance.com>
References: <cover.1683326865.git.peilin.ye@bytedance.com>
        <e6c4681dd9205d702ae2e6124e20c6210520e76e.1683326865.git.peilin.ye@bytedance.com>
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On Fri,  5 May 2023 17:16:10 -0700 Peilin Ye wrote:
>  		} else {
> -			dev_queue = dev_ingress_queue(dev);
> -			old = dev_graft_qdisc(dev_queue, new);
> +			old = dev_graft_qdisc(dev_queue, NULL);
> +
> +			/* {ingress,clsact}_destroy() "old" before grafting "new" to avoid
> +			 * unprotected concurrent accesses to net_device::miniq_{in,e}gress
> +			 * pointer(s) in mini_qdisc_pair_swap().
> +			 */
> +			qdisc_notify(net, skb, n, classid, old, new, extack);
> +			qdisc_destroy(old);
> +
> +			dev_graft_qdisc(dev_queue, new);

BTW can't @old be NULL here?