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Date: Wed, 8 Jan 2025 10:40:40 +0000
From: Simon Horman <horms@kernel.org>
To: Kuniyuki Iwashima <kuniyu@amazon.com>
Cc: "David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Andrew Lunn <andrew+netdev@lunn.ch>,
	Xiao Liang <shaw.leon@gmail.com>,
	Kuniyuki Iwashima <kuni1840@gmail.com>, netdev@vger.kernel.org,
	Pablo Neira Ayuso <pablo@netfilter.org>,
	Harald Welte <laforge@gnumonks.org>
Subject: Re: [PATCH v1 net 1/3] gtp: Use for_each_netdev_rcu() in
 gtp_genl_dump_pdp().
Message-ID: <20250108104040.GA7706@kernel.org>
References: <20250108062834.11117-1-kuniyu@amazon.com>
 <20250108062834.11117-2-kuniyu@amazon.com>
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In-Reply-To: <20250108062834.11117-2-kuniyu@amazon.com>

On Wed, Jan 08, 2025 at 03:28:32PM +0900, Kuniyuki Iwashima wrote:
> gtp_newlink() links the gtp device to a list in dev_net(dev).
> 
> However, even after the gtp device is moved to another netns,
> it stays on the list but should be invisible.
> 
> Let's use for_each_netdev_rcu() for netdev traversal in
> gtp_genl_dump_pdp().
> 
> Note that gtp_dev_list is no longer used under RCU, so list
> helpers are converted to the non-RCU variant.
> 
> Fixes: 459aa660eb1d ("gtp: add initial driver for datapath of GPRS Tunneling Protocol (GTP-U)")
> Reported-by: Xiao Liang <shaw.leon@gmail.com>
> Closes: https://lore.kernel.org/netdev/CABAhCOQdBL6h9M2C+kd+bGivRJ9Q72JUxW+-gur0nub_=PmFPA@mail.gmail.com/
> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> ---
> Cc: Pablo Neira Ayuso <pablo@netfilter.org>
> Cc: Harald Welte <laforge@gnumonks.org>

...

> @@ -2280,7 +2281,10 @@ static int gtp_genl_dump_pdp(struct sk_buff *skb,
>  		return 0;
>  
>  	rcu_read_lock();
> -	list_for_each_entry_rcu(gtp, &gn->gtp_dev_list, list) {
> +	for_each_netdev_rcu(net, dev) {
> +		if (dev->rtnl_link_ops != &gtp_link_ops)
> +			continue;
> +
>  		if (last_gtp && last_gtp != gtp)
>  			continue;
>  		else

Hi Iwashima-san,

With this change gtp seems to be uninitialised here.
And, also, it looks like gn is now set but otherwise unused in this function.

Flagged by W=1 builds with clang-19.

...