netdev - Re: [PATCH net-next] netlink: support dumping IPv4 multicast addresses

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Message-ID: <CADXeF1Fq+AimSZSf480D3Hgimzgk2eUCjs0XHNAq5jPkEPjwsA@mail.gmail.com>
Date: Tue, 17 Dec 2024 19:03:23 +0900
From: Yuyang Huang <yuyanghuang@...gle.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, David Ahern <dsahern@...nel.org>, 
	roopa@...ulusnetworks.com, jiri@...nulli.us, stephen@...workplumber.org, 
	jimictw@...gle.com, prohr@...gle.com, liuhangbin@...il.com, 
	nicolas.dichtel@...nd.com, andrew@...n.ch, netdev@...r.kernel.org, 
	Maciej Żenczykowski <maze@...gle.com>, 
	Lorenzo Colitti <lorenzo@...gle.com>
Subject: Re: [PATCH net-next] netlink: support dumping IPv4 multicast addresses

Hi Eric

Thanks for the suggestion.

>Have you tested your patch with LOCKDEP enabled ?

>CONFIG_PROVE_LOCKING=y

>I think this should splat, considering your use of for_each_pmc_rtnl()
>in a section where rtnl is not held.

>Please make sure to use RCU variant only in the dump operation.

After turn on CONFIG_PROVE_LOCKING=y, I can see the error like follows:

net/ipv4/devinet.c:1876 suspicious rcu_dereference_protected() usage!

I will fix it properly in the next patch version.

Thanks,
Yuyang



On Tue, Dec 17, 2024 at 4:07 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Tue, Dec 17, 2024 at 7:31 AM Yuyang Huang <yuyanghuang@...gle.com> wrote:
> >
> > Extended RTM_GETMULTICAST to support dumping joined IPv4 multicast
> > addresses, in addition to the existing IPv6 functionality. This allows
> > userspace applications to retrieve both IPv4 and IPv6 multicast
> > addresses through similar netlink command and then monitor future
> > changes by registering to RTNLGRP_IPV4_MCADDR and RTNLGRP_IPV6_MCADDR.
>
> Hi Yuyang
>
> Have you tested your patch with LOCKDEP enabled ?
>
> CONFIG_PROVE_LOCKING=y
>
> I think this should splat, considering your use of for_each_pmc_rtnl()
> in a section where rtnl is not held.
>
> Please make sure to use RCU variant only in the dump operation.