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From:   Jamal Hadi Salim <jhs@mojatatu.com>
Date:   Thu, 5 Oct 2023 07:46:55 -0400
Message-ID: <CAM0EoMkgUPF751LpEij4QjwsP_Z3qBMW_Nss67OVN1hxyN0mGQ@mail.gmail.com>
Subject: Re: [PATCH] net/sched: use spin_lock_bh() on &gact->tcf_lock
To:     Chengfeng Ye <dg573847474@gmail.com>
Cc:     Jakub Kicinski <kuba@kernel.org>, xiyou.wangcong@gmail.com,
        jiri@resnulli.us, davem@davemloft.net, edumazet@google.com,
        pabeni@redhat.com, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Horatiu Vultur <horatiu.vultur@microchip.com>
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On Thu, Oct 5, 2023 at 5:01=E2=80=AFAM Chengfeng Ye <dg573847474@gmail.com>=
 wrote:
>
> Hi Jakub,
>
> Thanks for the reply,
>
> I inspected the code a bit more, it seems that the TC action is called fr=
om
> 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@microchip.com>
Maybe that code needs to run in a tasklet?
In any case your patch is incorrect.

cheers,
jamal