netdev - Re: [PATCH net] bonding: only set speed/duplex to unknown, if getting speed failed

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Message-ID: <fef5419d-081d-4601-9ce6-f597beed7716@blackwall.org>
Date: Fri, 30 Jan 2026 18:07:28 +0200
From: Nikolay Aleksandrov <razor@...ckwall.org>
To: Jay Vosburgh <jv@...sburgh.net>, Hangbin Liu <liuhangbin@...il.com>
Cc: Thomas Bogendoerfer <tbogendoerfer@...e.de>,
 Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] bonding: only set speed/duplex to unknown, if getting
 speed failed

On 30/01/2026 17:38, Jay Vosburgh wrote:
> Hangbin Liu <liuhangbin@...il.com> wrote:
> 
>> On Fri, Jan 30, 2026 at 12:19:04PM +0100, Thomas Bogendoerfer wrote:
>>> bond_update_speed_duplex() first set speed/duplex to unknown and
>>> then asks slave driver for current speed/duplex. Since getting
>>> speed/duplex might take longer there is a race, where this false state
>>> is visible by /proc/net/bonding. With commit 691b2bf14946 ("bonding:
>>
>> The patch looks good to me. But based on your description, I don't think
>> the fixes tag is correct.
> 
> 	Agreed on both points; I suspect the origin of the race window
> is:
> 
> commit e9fe8efeeae11f19bb6fafd6153ec77deaeb4b83
> Author: Nikolay Aleksandrov <razor@...ckwall.org>
> Date:   Tue Sep 9 23:17:01 2014 +0200
> 
>      bonding: procfs: clean bond->lock usage and use RCU
> 
> 	as this patch converted some locking in the procfs logic to be
> solely RCU.
> 
> 	-J
> 

I don't think so. :-)
bond_update_speed_duplex() can sleep and has never been called with the write_lock.
See for example:
  commit 876254ae2758
  Author: Veaceslav Falico <vfalico@...hat.com>
  Date:   Tue Mar 12 06:31:32 2013 +0000

     bonding: don't call update_speed_duplex() under spinlocks

It seems to me that behaviour has always been there, regardless of having a
read_lock in procfs or not.

Cheers,
  Nik