netdev - Re: Questioning requirement for ASSERT

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Message-ID: <20210914072629.3d486b6b@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Tue, 14 Sep 2021 07:26:29 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Eli Cohen <elic@...dia.com>
Cc:     <john.hurley@...ronome.com>, <sriharsha.basavapatna@...adcom.com>,
        <ozsh@...lanox.com>, netdev <netdev@...r.kernel.org>
Subject: Re: Questioning requirement for ASSERT_RTNL in indirect code

On Tue, 14 Sep 2021 09:05:00 +0300 Eli Cohen wrote:
> I see the same assert and the same comment, "All callback list access
> should be protected by RTNL.", in the following locations
> 
> drivers/net/ethernet/broadcom/bnxt/bnxt_tc.c:1873
> drivers/net/ethernet/mellanox/mlx5/core/en/rep/tc.c:303
> drivers/net/ethernet/netronome/nfp/flower/offload.c:1770
> 
> I assume the source of this comment is the same. Can you guys explain
> why is this necessary?

Because most drivers (all but mlx5?) depend on rtnl_lock for
serializing tc offload operations.

> Currently, with
> 74fc4f828769 ("net: Fix offloading indirect devices dependency on qdisc order creation"
> 
> the assert will emit a warning into dmesg with no other noticable
> effect. I am thinking maybe we need to remove this assert.
> 
> Comments?

rtnl_lock must be held unless unlocked_driver_cb is set.