Re: [PATCH v6 4/9] futex: Create get_robust_list2() syscall

kernel test robot
2025-11-23T07:17:06Z

Hi André,

kernel test robot noticed the following build warnings:

[auto build test WARNING on c42ba5a87bdccbca11403b7ca8bad1a57b833732]

url: https://github.com/intel-lab-lkp/linux/commits/Andr-Almeida/futex-Use-explicit-sizes-for-compat_robust_list-structs/20251122-135406
base: c42ba5a87bdccbca11403b7ca8bad1a57b833732
patch link: https://lore.kernel.org/r/20251122-tonyk-robust_futex-v6-4-05fea005a0fd%40igalia.com
patch subject: [PATCH v6 4/9] futex: Create get_robust_list2() syscall
config: i386-randconfig-063-20251123 (https://download.01.org/0day-ci/archive/20251123/202511231423.O6KdcL8r-lkp@intel.com/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251123/202511231423.O6KdcL8r-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/202511231423.O6KdcL8r-lkp@intel.com/

sparse warnings: (new ones prefixed by >>)
>> kernel/futex/syscalls.c:200:22: 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:200:22: sparse: expected struct robust_list_head *head
kernel/futex/syscalls.c:200:22: sparse: got struct robust_list_head [noderef] __user *
>> kernel/futex/syscalls.c:202:24: sparse: sparse: incorrect type in initializer (different address spaces) @@ expected void [noderef] __user *__x @@ got struct robust_list_head *head @@
kernel/futex/syscalls.c:202:24: sparse: expected void [noderef] __user *__x
kernel/futex/syscalls.c:202:24: sparse: got struct robust_list_head *head

vim +200 kernel/futex/syscalls.c

160
161 SYSCALL_DEFINE4(get_robust_list2, int, pid,
162 void __user * __user *, head_ptr,
163 unsigned int, index, unsigned int, flags)
164 {
165 void __user *entry_ptr;
166 uintptr_t entry;
167
168 if (index >= FUTEX_ROBUST_LISTS_PER_USER)
169 return -EINVAL;
170
171 if (flags)
172 return -EINVAL;
173
174 /*
175 * The first two indexes are reserved for the kernel to be used with the
176 * legacy syscall, so we hide them from userspace.
177 *
178 * We map [0, FUTEX_ROBUST_LISTS_PER_USER) to
179 * [FUTEX_ROBUST_LIST2_IDX, FUTEX_ROBUST_LIST2_MAX_IDX)
180 */
181 index += FUTEX_ROBUST_LIST2_IDX;
182
183 entry_ptr = futex_get_robust_list_common(pid, false, index);
184 if (IS_ERR(entry_ptr))
185 return PTR_ERR(entry_ptr);
186
187 entry = (uintptr_t) entry_ptr;
188
189 if (entry & FUTEX_ROBUST_LIST_ENTRY_32BIT) {
190 entry &= FUTEX_ROBUST_LIST_ENTRY_MASK;
191
192 if (copy_to_user(head_ptr, &entry, sizeof(u32)))
193 return -EFAULT;
194
195 return 0;
196 } else {
197 struct robust_list_head *head;
198
199 entry &= FUTEX_ROBUST_LIST_ENTRY_MASK;
> 200 head = (__force struct robust_list_head __user *)entry;
201
> 202 return put_user(head, head_ptr);
203 }
204 }
205

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