netdev - Re: Questioning requirement for ASSERT

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Date:   Tue, 14 Sep 2021 17:54:39 +0300
From:   Eli Cohen <elic@...dia.com>
To:     Jakub Kicinski <kuba@...nel.org>
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, Sep 14, 2021 at 07:26:29AM -0700, Jakub Kicinski wrote:
> 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.
> 

But the assert I am referring to is called as part of setting up the
callback that will be used for offload operations, e.g. for adding a new
filter with tc. It's not the actual filter insetion code.

And as far as I can see this call sequence is already serialized by
flow_indr_block_lock.

> > 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.