netdev - Re: [PATCH net] team: replace team lock with rtnl lock

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Message-ID: <ae7e9800-e395-4b9e-9878-83a5e768cc98@I-love.SAKURA.ne.jp>
Date: Thu, 22 May 2025 22:47:19 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Network Development <netdev@...r.kernel.org>,
        Jiri Pirko <jiri@...nulli.us>, Andrew Lunn <andrew+netdev@...n.ch>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
        Hillf Danton <hdanton@...a.com>,
        Stanislav Fomichev <stfomichev@...il.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>
Subject: Re: [PATCH net] team: replace team lock with rtnl lock

On 2025/05/22 10:00, Tetsuo Handa wrote:
> On 2025/05/22 3:00, Jakub Kicinski wrote:
>> And as he pointed out this patch promptly generates all sort 
>> of locking warnings, please test this properly.
> 
> I didn't get any compile-time warnings, and
> https://lkml.kernel.org/r/682e6b1f.a00a0220.2a3337.0007.GAE@google.com didn't
> get any run-time locking warnings.
> 
> What locking warnings did you get? Is there an automated testing environment
> (like https://lkml.kernel.org/r/66a4b1a7.050a0220.12c792.8f9e@mx.google.com )
> which I can use for testing this patch?
> 

Ah, I got which posts you are referring to. I was failing to receive Jiri's mails
because my spam filter setting was sending mails from .us domain to trash.
Now I removed the .us entry.



Jiri Pirko wrote:
> Sat, May 17, 2025 at 09:32:20AM +0200, penguin-kernel@...ove.SAKURA.ne.jp wrote:
> 
> [..]
> 
> >@@ -2319,13 +2301,12 @@ static struct team *team_nl_team_get(struct genl_info *info)
> > 	}
> > 
> > 	team = netdev_priv(dev);
> >-	mutex_lock(&team->lock);
> > 	return team;
> > }
> 
> 
> Why do you think this is safe?
> 
> Rtnl is held only for set doit.

I assumed that the caller already held rtnl lock.

> 
> 
> > 
> > static void team_nl_team_put(struct team *team)
> > {
> >-	mutex_unlock(&team->lock);
> >+	ASSERT_RTNL();
> 
> Did you test this? How? Howcome you didn't hit this assertion?

Tests using syzbot's reproducer did not hit this assertion.

> 
> 
> > 	dev_put(team->dev);
> > }
> > 

Anyway, we can't remove team lock. Too bad.