netdev - Re: [PATCH v2 net-next 2/4] rtnetlink: Add per-netns RTNL.

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Message-ID: <20241004205104.69430-1-kuniyu@amazon.com>
Date: Fri, 4 Oct 2024 13:51:04 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <kuniyu@...zon.com>
CC: <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
	<kuni1840@...il.com>, <netdev@...r.kernel.org>, <pabeni@...hat.com>
Subject: Re: [PATCH v2 net-next 2/4] rtnetlink: Add per-netns RTNL.

From: Kuniyuki Iwashima <kuniyu@...zon.com>
Date: Fri, 4 Oct 2024 13:45:26 -0700
> From: Jakub Kicinski <kuba@...nel.org>
> Date: Fri, 4 Oct 2024 13:21:45 -0700
> > On Wed, 2 Oct 2024 08:12:38 -0700 Kuniyuki Iwashima wrote:
> > > +#ifdef CONFIG_DEBUG_NET_SMALL_RTNL
> > > +void __rtnl_net_lock(struct net *net);
> > > +void __rtnl_net_unlock(struct net *net);
> > > +void rtnl_net_lock(struct net *net);
> > > +void rtnl_net_unlock(struct net *net);
> > > +int rtnl_net_lock_cmp_fn(const struct lockdep_map *a, const struct lockdep_map *b);
> > > +#else
> > > +#define __rtnl_net_lock(net)
> > > +#define __rtnl_net_unlock(net)
> > > +#define rtnl_net_lock(net) rtnl_lock()
> > > +#define rtnl_net_unlock(net) rtnl_unlock()
> > 
> > Let's make sure net is always evaluated?
> > At the very least make sure the preprocessor doesn't eat it completely
> > otherwise we may end up with config-dependent "unused variable"
> > warnings down the line.
> 
> Sure, what comes to mind is void casting, which I guess is old-school
> style ?  Do you have any other idea or is this acceptable ?
> 
> #define __rtnl_net_lock(net) (void)(net)
> #define __rtnl_net_unlock(net) (void)(net)
> #define rtnl_net_lock(net)	\
> 	do {			\
> 		(void)(net);	\
> 		rtnl_lock();	\
> 	} while (0)
> #define rtnl_net_unlock(net)	\
> 	do {			\
> 		(void)(net);	\
> 		rtnl_unlock();	\
> 	} while (0)

or simply define these as static inline functions and
probably this is more preferable ?

static inline void __rtnl_net_lock(struct net *net) {}
static inline void __rtnl_net_unlock(struct net *net) {}
static inline void rtnl_net_lock(struct net *net)
{
	rtnl_lock();
}
static inline void rtnl_net_unlock(struct net *net)
{
	rtnl_unlock();
}