netdev - Re: [PATCH net] net: revert RTNL changes in unregister_netdevice_many

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Message-ID: <20250130004941.71433-1-kuniyu@amazon.com>
Date: Wed, 29 Jan 2025 16:49:41 -0800
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <edumazet@...gle.com>
CC: <davem@...emloft.net>, <eric.dumazet@...il.com>, <horms@...nel.org>,
	<kuba@...nel.org>, <netdev@...r.kernel.org>, <pabeni@...hat.com>,
	<syzbot+5b9196ecf74447172a9a@...kaller.appspotmail.com>, Kuniyuki Iwashima
	<kuniyu@...zon.com>
Subject: Re: [PATCH net] net: revert RTNL changes in unregister_netdevice_many_notify()

From: Eric Dumazet <edumazet@...gle.com>
Date: Wed, 29 Jan 2025 14:27:26 +0000
> This patch reverts following changes:
> 
> 83419b61d187 net: reduce RTNL hold duration in unregister_netdevice_many_notify() (part 2)
> ae646f1a0bb9 net: reduce RTNL hold duration in unregister_netdevice_many_notify() (part 1)
> cfa579f66656 net: no longer hold RTNL while calling flush_all_backlogs()
> 
> This caused issues in layers holding a private mutex:
> 
> cleanup_net()
>   rtnl_lock();
> 	mutex_lock(subsystem_mutex);
> 
> 	unregister_netdevice();
> 
> 	   rtnl_unlock();		// LOCKDEP violation
> 	   rtnl_lock();
> 
> I will revisit this in next cycle, opt-in for the new behavior
> from safe contexts only.
> 
> Fixes: cfa579f66656 ("net: no longer hold RTNL while calling flush_all_backlogs()")
> Fixes: ae646f1a0bb9 ("net: reduce RTNL hold duration in unregister_netdevice_many_notify() (part 1)")
> Fixes: 83419b61d187 ("net: reduce RTNL hold duration in unregister_netdevice_many_notify() (part 2)")
> Reported-by: syzbot+5b9196ecf74447172a9a@...kaller.appspotmail.com
> Closes: https://lore.kernel.org/netdev/6789d55f.050a0220.20d369.004e.GAE@google.com/
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@...zon.com>