netdev - Re: [RFC PATCH net-next 1/4] net-sysfs: remove rtnl

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Message-ID: <173710240479.5144.11769826495170395041@kwain>
Date: Fri, 17 Jan 2025 09:26:44 +0100
From: Antoine Tenart <atenart@...nel.org>
To: Jakub Kicinski <kuba@...nel.org>
Cc: davem@...emloft.net, pabeni@...hat.com, edumazet@...gle.com, netdev@...r.kernel.org, gregkh@...uxfoundation.org, mhocko@...e.com, stephen@...workplumber.org
Subject: Re: [RFC PATCH net-next 1/4] net-sysfs: remove rtnl_trylock from device attributes

Quoting Jakub Kicinski (2025-01-17 00:43:19)
> On Thu, 16 Jan 2025 15:42:41 -0800 Jakub Kicinski wrote:
> > On Thu, 16 Jan 2025 14:36:17 +0100 Antoine Tenart wrote:
> > > While refreshing the series, especially after adding the dev_isalive()
> > > check, I found out we actually do not need to drop the sysfs protection
> > > and hold a reference to the net device during the whole rtnl locking
> > > section. This is because after getting the rtnl lock and once we know
> > > the net device dismantle hasn't started yet, we're sure dismantle won't
> > > start (and the device won't be freed) until we give back the rtnl lock.
> > > 
> > > This makes the new helpers easier to use, does not require to expose
> > > the kernfs node to users, making the code more contained; but the
> > > locking order is not as perfect.
> > > 
> > > We would go from (version 1),
> > > 
> > > 1. unlocking sysfs
> > > 2. locking rtnl
> > > 3. unlocking rtnl
> > > 4. locking sysfs
> > > 
> > > to (version 2),
> > > 
> > > 1. unlocking sysfs
> > > 2. locking rtnl
> > > 3. locking sysfs
> > > 4. unlocking rtnl
> > > 
> > > This is actually fine because the "sysfs lock" isn't a lock but a
> > > refcnt, with the only deadlock situation being when draining it.
> > > 
> > > Version 1: https://github.com/atenart/linux/commit/596c5d9895ccdb75057978abd6be1a42ee4b448e
> > > Version 2: https://github.com/atenart/linux/commit/c6659bb26f564f1fd63d1c279616f57141e9f2bf
> > > 
> > > Thoughts? Apart from that question, either series is ready for
> > > submission.  
> > 
> > Nice, yes, I think that works!
> 
> To be clear - by "that" I mean version 2 :)

Thanks! Will send version 2 then.