Re: [linux-next:master 4429/6545] fs/kernfs/dir.c:751:31: sparse: sparse: cast to non-scalar

[Shakeel Butt <shakeel.butt@linux.dev>]

+Will

On Tue, Sep 15, 2026 at 08:51:41PM +0800, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> head:   1a1de54f7369cd2b5bac0f265910e60ad3a6b4c3
> commit: 81bdc85b4c086502f4446a58eb5d25f29bb5e9f7 [4429/6545] kernfs: fix up the unlocked attribute reads on the creation paths
> config: alpha-randconfig-r121-20260915 (https://download.01.org/0day-ci/archive/20260915/202609152007.ZrNbQ8XS-lkp@intel.com/config)
> compiler: alpha-linux-gcc (GCC) 8.5.0
> sparse: v0.6.5-rc1
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260915/202609152007.ZrNbQ8XS-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/202609152007.ZrNbQ8XS-lkp@intel.com/
> 
> sparse warnings: (new ones prefixed by >>)
> >> fs/kernfs/dir.c:751:31: sparse: sparse: cast to non-scalar
> >> fs/kernfs/dir.c:751:31: sparse: sparse: cast from non-scalar
> 
> vim +751 fs/kernfs/dir.c
> 
>    731	
>    732	struct kernfs_node *kernfs_new_node(struct kernfs_node *parent,
>    733					    const char *name, umode_t mode,
>    734					    kuid_t uid, kgid_t gid,
>    735					    unsigned flags)
>    736	{
>    737		struct kernfs_node *kn;
>    738	
>    739		/*
>    740		 * The mode and the gid below are read unlocked on purpose: they feed
>    741		 * a node that does not exist yet, so nothing orders a racing chmod or
>    742		 * chown against this creation.
>    743		 */
>    744		if (READ_ONCE(parent->mode) & S_ISGID) {
>    745			/* this code block imitates inode_init_owner() for
>    746			 * kernfs
>    747			 */
>    748			struct kernfs_iattrs *attrs = READ_ONCE(parent->iattr);
>    749	
>    750			if (attrs)
>  > 751				gid = READ_ONCE(attrs->ia_gid);

This seems to be related to READ_ONCE() implementation of alpha. ISO C only
permits a cast to a scalar type but gcc/clang accept casting a struct to its own
type as an extension. It seems like sparse implements the standard rule. I think
we can ignore this (or sparse should handle it as gcc/clang).

>    752	
>    753			if (flags & KERNFS_DIR)
>    754				mode |= S_ISGID;
>    755		}
>    756	
>    757		kn = __kernfs_new_node(kernfs_root(parent), parent,
>    758				       name, mode, uid, gid, flags);
>    759		return kn;
>    760	}
>    761	
> 
> --
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki