netdev - Re: [net 05/11] net/mlx5e: Hold reference on mirred devices while accessing them

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Date:   Tue, 7 Jul 2020 19:57:23 +0300
From:   Or Gerlitz <gerlitz.or@...il.com>
To:     Eli Cohen <eli@...lanox.com>
Cc:     Saeed Mahameed <saeedm@...lanox.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Linux Netdev List <netdev@...r.kernel.org>,
        Vlad Buslov <vladbu@...lanox.com>
Subject: Re: [net 05/11] net/mlx5e: Hold reference on mirred devices while
 accessing them

On Tue, Jul 7, 2020 at 5:57 PM Eli Cohen <eli@...lanox.com> wrote:
> On Mon, Jul 06, 2020 at 09:13:06AM +0300, Or Gerlitz wrote:
> > On Sun, Jul 5, 2020 at 10:19 AM Eli Cohen <eli@...lanox.com> wrote:
> >
> > so what are we protecting here against? someone removing the device
> > while the tc rule is being added?
> >
> Not necessairly. In case of ecmp, the rule may be copied to another
> eswitch. At this time, if the mirred device does not exsist anymore, we
> will crash.
>
> I saw this problem at a customer's machine and this solved the problem.
> It was an older kernel but I think we have the same issue here as well.
> All you have is the ifindex of the mirred device so what I did here is
> required.

Repeating myself, why do it in the driver and not higher in the tc stack?
if I got you correctly, the same problem can happen for sw only (skip-hw) rules