Re: [PATCH v1 net-next 05/11] ipv4: Use per-netns RTNL helpers in inet_rtm_newaddr().

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: kernel test robot <lkp@intel.com>
Date: Sun, 20 Oct 2024 04:03:55 +0800
> Hi Kuniyuki,
> 
> kernel test robot noticed the following build warnings:
> 
> [auto build test WARNING on net-next/main]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Kuniyuki-Iwashima/rtnetlink-Define-RTNL_FLAG_DOIT_PERNET-for-per-netns-RTNL-doit/20241018-092802
> base:   net-next/main
> patch link:    https://lore.kernel.org/r/20241018012225.90409-6-kuniyu%40amazon.com
> patch subject: [PATCH v1 net-next 05/11] ipv4: Use per-netns RTNL helpers in inet_rtm_newaddr().
> config: x86_64-randconfig-122-20241019 (https://download.01.org/0day-ci/archive/20241020/202410200325.SaEJmyZS-lkp@intel.com/config)
> compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20241020/202410200325.SaEJmyZS-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202410200325.SaEJmyZS-lkp@intel.com/
> 
> sparse warnings: (new ones prefixed by >>)
> >> net/ipv4/devinet.c:941:9: sparse: sparse: incorrect type in argument 2 (different address spaces) @@     expected void *p @@     got struct in_ifaddr [noderef] __rcu *ifa_list @@
>    net/ipv4/devinet.c:941:9: sparse:     expected void *p
>    net/ipv4/devinet.c:941:9: sparse:     got struct in_ifaddr [noderef] __rcu *ifa_list

Hmm.. when DEBUG_NET_SMALL_RTNL is off, we use static inline helper
returning (void *) to make sure net is always evaluated as requested
in this thread.

  https://lore.kernel.org/netdev/20241004132145.7fd208e9@kernel.org/

But it seems we can't do that when the pointer has __rcu annotation.

Also, this (void *)net evaluation  in turn makes build fail due to
-Werror=unused-value.

  #define rtnl_net_dereference(net, p)			\
  	({						\
  		(void *)net;				\
  		rtnl_dereference(p);			\
  	})

  net/ipv4/devinet.c: In function ‘inet_rtm_deladdr’:
  ./include/linux/rtnetlink.h:154:17: error: statement with no effect [-Werror=unused-value]
    154 |                 (void *)net;                            \
  net/ipv4/devinet.c:674:21: note: in expansion of macro ‘rtnl_net_dereference’
    674 |              (ifa = rtnl_net_dereference(net, *ifap)) != NULL;
        |                     ^~~~~~~~~~~~~~~~~~~~


So, we need to go back to the simplest macro.

  #define rtnl_net_dereference(net, p)			\
  	rtnl_dereference(p);

I'll include the fix in v2.


> >> net/ipv4/devinet.c:941:9: sparse: sparse: incorrect type in argument 2 (different address spaces) @@     expected void *p @@     got struct in_ifaddr [noderef] __rcu *ifa_next @@
>    net/ipv4/devinet.c:941:9: sparse:     expected void *p
>    net/ipv4/devinet.c:941:9: sparse:     got struct in_ifaddr [noderef] __rcu *ifa_next
>    net/ipv4/devinet.c: note: in included file:
> >> include/linux/inetdevice.h:261:54: sparse: sparse: incorrect type in argument 2 (different address spaces) @@     expected void *p @@     got struct in_device [noderef] __rcu *const ip_ptr @@
>    include/linux/inetdevice.h:261:54: sparse:     expected void *p
>    include/linux/inetdevice.h:261:54: sparse:     got struct in_device [noderef] __rcu *const ip_ptr
>    net/ipv4/devinet.c: note: in included file (through include/linux/inetdevice.h):
> >> include/linux/rtnetlink.h:147:16: sparse: sparse: incompatible types in comparison expression (different address spaces):
>    include/linux/rtnetlink.h:147:16: sparse:    void [noderef] __rcu *
>    include/linux/rtnetlink.h:147:16: sparse:    void *
> >> include/linux/rtnetlink.h:147:16: sparse: sparse: incompatible types in comparison expression (different address spaces):
>    include/linux/rtnetlink.h:147:16: sparse:    void [noderef] __rcu *
>    include/linux/rtnetlink.h:147:16: sparse:    void *
> >> include/linux/rtnetlink.h:147:16: sparse: sparse: incompatible types in comparison expression (different address spaces):
>    include/linux/rtnetlink.h:147:16: sparse:    void [noderef] __rcu *
>    include/linux/rtnetlink.h:147:16: sparse:    void *
> 
> vim +941 net/ipv4/devinet.c
> 
>    935	
>    936	static struct in_ifaddr *find_matching_ifa(struct net *net, struct in_ifaddr *ifa)
>    937	{
>    938		struct in_device *in_dev = ifa->ifa_dev;
>    939		struct in_ifaddr *ifa1;
>    940	
>  > 941		in_dev_for_each_ifa_rtnl_net(net, ifa1, in_dev) {
>    942			if (ifa1->ifa_mask == ifa->ifa_mask &&
>    943			    inet_ifa_match(ifa1->ifa_address, ifa) &&
>    944			    ifa1->ifa_local == ifa->ifa_local)
>    945				return ifa1;
>    946		}
>    947	
>    948		return NULL;
>    949	}
>    950