netdev - Re: for_each_netdev_rcu() protected by RTNL and CONFIG_PROVE_RCU

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Message-ID: <20250207-active-solid-vole-26a2c6@leitao>
Date: Fri, 7 Feb 2025 02:46:21 -0800
From: Breno Leitao <leitao@...ian.org>
To: Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: andrew+netdev@...n.ch, edumazet@...gle.com, kernel-team@...a.com,
	kuba@...nel.org, netdev@...r.kernel.org, ushankar@...estorage.com
Subject: Re: for_each_netdev_rcu() protected by RTNL and CONFIG_PROVE_RCU_LIST

Hello Kuniyuki,

On Fri, Feb 07, 2025 at 12:38:22PM +0900, Kuniyuki Iwashima wrote:
> From: Breno Leitao <leitao@...ian.org>
> Date: Thu, 6 Feb 2025 07:51:55 -0800

> > Are there better approaches to silence these warnings when RTNL is held?
> > Any suggestions would be appreciated.
> 
> We can't use lockdep_rtnl_net_is_held() there yet because most users are
> not converted to per-netns RTNL, so it will complain loudly.

Right, so, I understand the best approach is to leverage
lockdep_rtnl_is_held() only right now. Something as:

	diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
	index 1dcc76af75203..0deee1313f23a 100644
	--- a/include/linux/netdevice.h
	+++ b/include/linux/netdevice.h
	@@ -3217,7 +3217,8 @@ int call_netdevice_notifiers_info(unsigned long val,
	#define for_each_netdev_reverse(net, d)        \
			list_for_each_entry_reverse(d, &(net)->dev_base_head, dev_list)
	#define for_each_netdev_rcu(net, d)            \
	-               list_for_each_entry_rcu(d, &(net)->dev_base_head, dev_list)
	+               list_for_each_entry_rcu(d, &(net)->dev_base_head, dev_list, \
	+                                       lockdep_rtnl_is_held())
	#define for_each_netdev_safe(net, d, n)        \
			list_for_each_entry_safe(d, n, &(net)->dev_base_head, dev_list)
	#define for_each_netdev_continue(net, d)               \

Which brings another problem:

lockdep_rtnl_is_held() is defined in include/linux/rtnetlink.h, so,
we'll need to include 'linux/rtnetlink.h' in linux/netdevice.h, which
doesn't seem correct (!?).

Otherwise drivers using for_each_netdev_rcu() will not be able to find
lockdep_rtnl_is_held().

I suppose we will need to move some of definitions around, but, I am
confident in which way.

--breno