kernel/futex/syscalls.c:204:22: sparse: sparse: incorrect type in assignment (different address spaces)

[kernel test robot <lkp@intel.com>]

tree:   https://github.com/intel-lab-lkp/linux/commits/Andr-Almeida/futex-Skip-test_futex_robust_unlock-if-not-supported/20260925-145324
head:   0a151b703cae864a3bab66cc7fb5b8dc983658d3
commit: 8e4b5fd01bb4f8850e3f022e267d4fc53678c8fe futex: Create get_robust_list2() syscall
date:   5 days ago
config: m68k-randconfig-r2300-20260930 (https://download.01.org/0day-ci/archive/20260930/202609301514.dUuYTMaT-lkp@intel.com/config)
compiler: m68k-linux-gcc (GCC) 12.5.0
sparse: v0.6.5-rc1
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260930/202609301514.dUuYTMaT-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/202609301514.dUuYTMaT-lkp@intel.com/

sparse warnings: (new ones prefixed by >>)
>> kernel/futex/syscalls.c:204:22: sparse: sparse: incorrect type in assignment (different address spaces) @@     expected struct robust_list_head *head @@     got struct robust_list_head [noderef] __user * @@
   kernel/futex/syscalls.c:204:22: sparse:     expected struct robust_list_head *head
   kernel/futex/syscalls.c:204:22: sparse:     got struct robust_list_head [noderef] __user *
>> kernel/futex/syscalls.c:206:24: sparse: sparse: incorrect type in initializer (different address spaces) @@     expected void [noderef] __user *__x @@     got struct robust_list_head *head @@
   kernel/futex/syscalls.c:206:24: sparse:     expected void [noderef] __user *__x
   kernel/futex/syscalls.c:206:24: sparse:     got struct robust_list_head *head

vim +204 kernel/futex/syscalls.c

   164	
   165	SYSCALL_DEFINE4(get_robust_list2, int, pid,
   166			void __user * __user *, head_ptr,
   167			unsigned int, index, unsigned int, flags)
   168	{
   169		void __user *entry_ptr;
   170		uintptr_t entry;
   171	
   172		if (index >= FUTEX_ROBUST_LISTS_PER_USER)
   173			return -EINVAL;
   174	
   175		if (flags)
   176			return -EINVAL;
   177	
   178		/*
   179		 * The first two indexes are reserved for the kernel to be used with the
   180		 * legacy syscall, so we hide them from userspace.
   181		 *
   182		 * We map [0, FUTEX_ROBUST_LISTS_PER_USER) to
   183		 *  [FUTEX_ROBUST_LIST2_IDX, FUTEX_ROBUST_LIST2_MAX_IDX)
   184		 */
   185		index += FUTEX_ROBUST_LIST2_IDX;
   186	
   187		entry_ptr = futex_get_robust_list_common(pid, false, index);
   188		if (IS_ERR(entry_ptr))
   189			return PTR_ERR(entry_ptr);
   190	
   191		entry = (uintptr_t) entry_ptr;
   192	
   193		if (entry & FUTEX_ROBUST_LIST_ENTRY_32BIT) {
   194			entry &= FUTEX_ROBUST_LIST_ENTRY_MASK;
   195	
   196			if (copy_to_user(head_ptr, &entry, sizeof(u32)))
   197				return -EFAULT;
   198	
   199			return 0;
   200		} else {
   201			struct robust_list_head *head;
   202	
   203			entry &= FUTEX_ROBUST_LIST_ENTRY_MASK;
 > 204			head = (__force struct robust_list_head __user *)entry;
   205	
 > 206			return put_user(head, head_ptr);
   207		}
   208	}
   209	

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