netdev - Re: [PATCH net] l2tp: fix lockdep splat

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Message-ID: <Zrj7ggOFooYu0hHE@pop-os.localdomain>
Date: Sun, 11 Aug 2024 10:57:22 -0700
From: Cong Wang <xiyou.wangcong@...il.com>
To: James Chapman <jchapman@...alix.com>
Cc: netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
	kuba@...nel.org, pabeni@...hat.com, dsahern@...nel.org,
	tparkin@...alix.com,
	syzbot+6acef9e0a4d1f46c83d4@...kaller.appspotmail.com,
	gnault@...hat.com, cong.wang@...edance.com
Subject: Re: [PATCH net] l2tp: fix lockdep splat

On Tue, Aug 06, 2024 at 05:06:26PM +0100, James Chapman wrote:
> diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
> index c80ab3f26084..2e86f520f799 100644
> --- a/net/l2tp/l2tp_core.c
> +++ b/net/l2tp/l2tp_core.c
> @@ -86,6 +86,11 @@
>  /* Default trace flags */
>  #define L2TP_DEFAULT_DEBUG_FLAGS	0
>  
> +#define L2TP_DEPTH_NESTING		2
> +#if L2TP_DEPTH_NESTING == SINGLE_DEPTH_NESTING
> +#error "L2TP requires its own lockdep subclass"
> +#endif

This looks a bit over-engineering.

Why not just #define L2TP_DEPTH_NESTING SINGLE_DEPTH_NESTING+1?

Thanks.