Re: [linux-next:master 4018/13846] drivers/net/tun.c:2375:24: sparse: sparse: cast to non-scalar

On Sun, Aug 9, 2026 at 11:33 PM kernel test robot <[email protected]> wrote:
>
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> head:   6b8c8af514d739d0335f5579b585e02babe8a727
> commit: 23dad2d088dfc82cae1f5a936f8ff7ffebb38dd9 [4018/13846] tun: no longer rely on RTNL in tun_fill_info()
> config: alpha-randconfig-r134-20260810 (https://download.01.org/0day-ci/archive/20260810/[email protected]/config)
> compiler: alpha-linux-gcc (GCC) 14.3.0
> sparse: v0.6.5-rc1
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260810/[email protected]/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 <[email protected]>
> | Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
>
> sparse warnings: (new ones prefixed by >>)
> >> drivers/net/tun.c:2375:24: sparse: sparse: cast to non-scalar
> >> drivers/net/tun.c:2375:24: sparse: sparse: cast from non-scalar
>    drivers/net/tun.c:2376:24: sparse: sparse: cast to non-scalar
>    drivers/net/tun.c:2376:24: sparse: sparse: cast from non-scalar
>
> vim +2375 drivers/net/tun.c
>
>   2370
>   2371  static int tun_fill_info(struct sk_buff *skb, const struct net_device *dev)
>   2372  {
>   2373          const struct tun_struct *tun = netdev_priv(dev);
>   2374          unsigned int flags = READ_ONCE(tun->flags);
> > 2375          kuid_t owner = READ_ONCE(tun->owner);

I guess this would need to be owner.val and group.val to silence this
warning. Both from and to arguments.

That approach would not improve readability.

Types:

typedef struct {
        uid_t val;
} kuid_t;

typedef struct {
        gid_t val;
} kgid_t;

Whatever we choose to do (if anything), probably also applies to sk_uid:

static inline kuid_t sk_uid(const struct sock *sk)
{
        /* Paired with WRITE_ONCE() in sockfs_setattr() */
        return READ_ONCE(sk->sk_uid);
}

Another helper, make_kuid, uses a KUIDT_INIT wrapper to cast to the struct type.