linux-kernel - Re: [PATCH] net/sched: use spin_lock_bh() on &gact->tcf

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Date:   Thu, 5 Oct 2023 07:46:55 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Chengfeng Ye <dg573847474@...il.com>
Cc:     Jakub Kicinski <kuba@...nel.org>, xiyou.wangcong@...il.com,
        jiri@...nulli.us, davem@...emloft.net, edumazet@...gle.com,
        pabeni@...hat.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Horatiu Vultur <horatiu.vultur@...rochip.com>
Subject: Re: [PATCH] net/sched: use spin_lock_bh() on &gact->tcf_lock

On Thu, Oct 5, 2023 at 5:01 AM Chengfeng Ye <dg573847474@...il.com> wrote:
>
> Hi Jakub,
>
> Thanks for the reply,
>
> I inspected the code a bit more, it seems that the TC action is called from
> tcf_proto_ops.classify() callback, which is called from Qdisc_ops enqueue
> callback.
>
> Then Qdisc enqueue callback is from
>
> -> __dev_queue_xmit()
> -> __dev_xmit_skb()
> -> dev_qdisc_enqueue()
>
> inside the net core. It seems that this __dev_queue_xmit() callback is
> typically called from BH context (e.g.,  NET_TX_SOFTIRQ) with BH
> already disabled, but sometimes also can from a work queue under
> process context, one case is the br_mrp_test_work_expired() inside
> net/bridge/br_mrp.c. Does it indicate that this TC action could also be
> called with BH enable? I am not a developer so really not sure about it,
> as the networking code is a bit long and complicated.

net/bridge/br_mrp.c seems to need some love +Cc Horatiu Vultur
<horatiu.vultur@...rochip.com>
Maybe that code needs to run in a tasklet?
In any case your patch is incorrect.

cheers,
jamal