netdev - Re: [PATCH net v2] net/sched: act

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Date:   Mon, 24 Apr 2023 15:10:11 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Jamal Hadi Salim <jhs@...atatu.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Leon Romanovsky <leon@...nel.org>,
        Victor Nogueira <victor@...atatu.com>, davem@...emloft.net,
        edumazet@...gle.com, pabeni@...hat.com, netdev@...r.kernel.org,
        xiyou.wangcong@...il.com, jiri@...nulli.us, kernel@...atatu.com
Subject: Re: [PATCH net v2] net/sched: act_mirred: Add carrier check

On Mon, 24 Apr 2023 17:53:03 -0400
Jamal Hadi Salim <jhs@...atatu.com> wrote:

> On Mon, Apr 24, 2023 at 5:36 PM Jakub Kicinski <kuba@...nel.org> wrote:
> >
> > On Mon, 24 Apr 2023 13:59:15 -0400 Jamal Hadi Salim wrote:  
> > > > Then fix the driver. It shouldn't hang.
> > > > Other drivers just drop packets if link is down.  
> > >
> > > We didnt do extensive testing of drivers but consider this a safeguard
> > > against buggy driver (its a huge process upgrading drivers in some
> > > environments). It may even make sense to move this to dev_queue_xmit()
> > > i.e the arguement is: why is the core sending a packet to hardware
> > > that has link down to begin with? BTW, I believe the bridge behaves
> > > this way ...  
> >
> > I'm with Stephen, even if the check makes sense in general we should
> > first drill down into the real bug, and squash it.  
> 
> Ok then, I guess in keeping up with the spirit of trivial patches
> generating the most discussion, these are two separate issues in my
> opinion: IOW, the driver bug should be fixed (we have reached out to
> the  vendor) - but the patch stands on its own.

There are many other ways packet could arrive at driver when link
is down. You are addressing only one small corner case by patching
mirred.