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

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Date: Mon, 9 Oct 2023 08:35:49 +0200
From: Horatiu Vultur <horatiu.vultur@...rochip.com>
To: Jamal Hadi Salim <jhs@...atatu.com>
CC: Chengfeng Ye <dg573847474@...il.com>, 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>
Subject: Re: [PATCH] net/sched: use spin_lock_bh() on &gact->tcf_lock

The 10/05/2023 07:46, Jamal Hadi Salim wrote:

Hi Jamal,

> 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.

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.

> 
> cheers,
> jamal
> 

-- 
/Horatiu