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From:   Jamal Hadi Salim <jhs@mojatatu.com>
Date:   Mon, 9 Oct 2023 11:52:11 -0400
Message-ID: <CAM0EoMkYSs9oX+343OpkYbEFPPFcdEEaa92jnwmyzK2gqdKy2A@mail.gmail.com>
Subject: Re: [PATCH] net/sched: use spin_lock_bh() on &gact->tcf_lock
To:     Horatiu Vultur <horatiu.vultur@microchip.com>
Cc:     Chengfeng Ye <dg573847474@gmail.com>,
        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
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On Mon, Oct 9, 2023 at 2:36=E2=80=AFAM Horatiu Vultur
<horatiu.vultur@microchip.com> wrote:
>
> The 10/05/2023 07:46, Jamal Hadi Salim wrote:
>
> Hi Jamal,
>
> > 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 calle=
d from
> > > tcf_proto_ops.classify() callback, which is called from Qdisc_ops enq=
ueue
> > > 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 i=
s
> > > 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.
>
> I am currently out traveling and it would be a little bit hard for me to
> look at this right now. I can have a look after I come back in office
> around mid November.
> But I was wondering if this is stil an issue for MRP as Cong Wang
> pointed out, the function __dev_queue_xmit is already disabling the BH.

Yeah, sorry - should have read the code. Cong is right, there's
nothing for you to do.

cheers,
jamal

> >
> > cheers,
> > jamal
> >
>
> --
> /Horatiu