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

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Date: Thu, 13 Jun 2024 12:44:28 +0200
From: Przemek Kitszel <przemyslaw.kitszel@...el.com>
To: Larysa Zaremba <larysa.zaremba@...el.com>, Jakub Kicinski
	<kuba@...nel.org>
CC: Maciej Fijalkowski <maciej.fijalkowski@...el.com>, Jesper Dangaard Brouer
	<hawk@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
	<netdev@...r.kernel.org>, John Fastabend <john.fastabend@...il.com>, "Alexei
 Starovoitov" <ast@...nel.org>, Eric Dumazet <edumazet@...gle.com>, "Michal
 Kubiak" <michal.kubiak@...el.com>, Tony Nguyen <anthony.l.nguyen@...el.com>,
	<magnus.karlsson@...el.com>, <intel-wired-lan@...ts.osuosl.org>,
	<bpf@...r.kernel.org>, Paolo Abeni <pabeni@...hat.com>, "David S. Miller"
	<davem@...emloft.net>, <linux-kernel@...r.kernel.org>
Subject: Re: [Intel-wired-lan] [PATCH iwl-net 0/3] ice: fix synchronization
 between .ndo_bpf() and reset

On 6/13/24 10:54, Larysa Zaremba wrote:
> On Wed, Jun 12, 2024 at 02:09:35PM -0700, Jakub Kicinski wrote:
>> 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.
>>
> 
> I know, but __netif_queue_set_napi() requires rtnl_lock() inside the potential
> critical section and creates a deadlock this way. However, after reading
> patches that introduce this function, I think it is called too early in the
> configuration. Seems like it should be called somewhere right after
> netif_set_real_num_rx/_tx_queues(), much later in the configuration where we
> already hold the rtnl_lock(). In such way, ice_vsi_rebuild() could be protected
> with an internal mutex. WDYT?
> 
>>> 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).

for the reference, it was to Dawid here:
https://lore.kernel.org/netdev/20240610194756.5be5be90@kernel.org/

> 
> AFAIK, netif_device_detach() does not affect .ndo_bpf() calls. We were trying
> such approach with idpf and it does work for ethtool, but not for XDP.