netdev - Re: [PATCH net] ipv4: ip_tunnel: Fix suspicious RCU usage warning in ip_tunnel

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Message-ID: <ZxdoY8Uehc3qs89P@shredder.mtl.com>
Date: Tue, 22 Oct 2024 11:54:59 +0300
From: Ido Schimmel <idosch@...dia.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
	pabeni@...hat.com, dsahern@...nel.org, horms@...nel.org,
	pshelar@...ira.com
Subject: Re: [PATCH net] ipv4: ip_tunnel: Fix suspicious RCU usage warning in
 ip_tunnel_find()

On Tue, Oct 22, 2024 at 09:26:11AM +0200, Eric Dumazet wrote:
> I was looking at this recently, and my thinking is the following :
> 
> 1) ASSERT_RTNL() is adding code even on non debug kernels.
> 
> 2) It does not check if the current thread is owning the RTNL mutex,
> only that _some_ thread is owning it.
> 
> I would think that using lockdep_rtnl_is_held() would be better ?

Yes, agree. I see I did the same thing in 7f6f32bb7d335. Will post v2
tomorrow unless you prefer to submit it yourself (I don't mind).

Thanks

> 
> diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
> index d591c73e2c0e53efefb8fb9262610cbbd1dd71ea..25505f9b724c33d2c3ec2fca5355d7fdd4e01c14
> 100644
> --- a/net/ipv4/ip_tunnel.c
> +++ b/net/ipv4/ip_tunnel.c
> @@ -218,7 +218,7 @@ static struct ip_tunnel *ip_tunnel_find(struct
> ip_tunnel_net *itn,
> 
>         ip_tunnel_flags_copy(flags, parms->i_flags);
> 
> -       hlist_for_each_entry_rcu(t, head, hash_node) {
> +       hlist_for_each_entry_rcu(t, head, hash_node, lockdep_rtnl_is_held()) {
>                 if (local == t->parms.iph.saddr &&
>                     remote == t->parms.iph.daddr &&
>                     link == READ_ONCE(t->parms.link) &&