netdev - Re: [PATCH iwl-net 0/3] ice: fix synchronization between .ndo

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Date: Wed, 12 Jun 2024 14:09:35 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Larysa Zaremba <larysa.zaremba@...el.com>
Cc: <intel-wired-lan@...ts.osuosl.org>, Jesse Brandeburg
 <jesse.brandeburg@...el.com>, Tony Nguyen <anthony.l.nguyen@...el.com>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Alexei Starovoitov
 <ast@...nel.org>, "Daniel Borkmann" <daniel@...earbox.net>, Jesper Dangaard
 Brouer <hawk@...nel.org>, John Fastabend <john.fastabend@...il.com>, Maciej
 Fijalkowski <maciej.fijalkowski@...el.com>, <netdev@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, <bpf@...r.kernel.org>,
 <magnus.karlsson@...el.com>, Michal Kubiak <michal.kubiak@...el.com>
Subject: Re: [PATCH iwl-net 0/3] ice: fix synchronization between .ndo_bpf()
 and reset

On Wed, 12 Jun 2024 08:56:38 +0200 Larysa Zaremba wrote:
> On Tue, Jun 11, 2024 at 07:38:37PM -0700, Jakub Kicinski wrote:
> > On Mon, 10 Jun 2024 17:37:12 +0200 Larysa Zaremba wrote:  
> > > Fix the problems that are triggered by tx_timeout and ice_xdp() calls,
> > > including both pool and program operations.  
> > 
> > Is there really no way for ice to fix the locking? :(
> > The busy loops and trylocks() are not great, and seem like duct tape.
> 
> The locking mechanisms I use here do not look pretty, but if I am not missing 
> anything, the synchronization they provide must be robust.

Robust as in they may be correct here, but you lose lockdep and all
other infra normal mutex would give you.

> A prettier way of protecting the same critical sections would be replacing 
> ICE_CFG_BUSY around ice_vsi_rebuild() with rtnl_lock(), this would eliminate 
> locking code from .ndo_bpf() altogether, ice_rebuild_pending() logic will have 
> to stay.
> 
> At some point I have decided to avoid using rtnl_lock(), if I do not have to. I 
> think this is a goal worth pursuing?

Is the reset for failure recovery, rather than reconfiguration? 
If so netif_device_detach() is generally the best way of avoiding
getting called (I think I mentioned it to someone @intal recently).