netdev - Re: Questioning requirement for ASSERT

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Date:   Tue, 14 Sep 2021 08:07:46 -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 17:54:39 +0300 Eli Cohen wrote:
> 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.

Hm, indeed, should've looked at the code. There doesn't seem to be
anything on the driver side this is protecting. The assert was added
before the flow/nftables rewrite of the infra, perhaps that's the
answer. IOW the lock did not exist back then.