Re: [PATCH v8 10/10] futex: Use new robust list API internally

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

Hi André,

kernel test robot noticed the following build warnings:

[auto build test WARNING on 9f74092fda91ef93c2b07585785c1dc83cd7971f]

url:    https://github.com/intel-lab-lkp/linux/commits/Andr-Almeida/futex-Skip-test_futex_robust_unlock-if-not-supported/20261115-143110
base:   9f74092fda91ef93c2b07585785c1dc83cd7971f
patch link:    https://lore.kernel.org/r/20261115-tonyk-robust_futex-v8-10-a4fe47333a28%40igalia.com
patch subject: [PATCH v8 10/10] futex: Use new robust list API internally
config: x86_64-allnoconfig (https://download.01.org/0day-ci/archive/20261116/202611160419.vIdH20Tu-lkp@intel.com/config)
compiler: clang version 22.1.8 (https://github.com/llvm/llvm-project ca7933e47d3a3451d81e72ac174dcb5aa28b59d1)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20261116/202611160419.vIdH20Tu-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/202611160419.vIdH20Tu-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> kernel/futex/syscalls.c:75:6: warning: variable 'head' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
      75 |         if (index >= 0) {
         |             ^~~~~~~~~~
   kernel/futex/syscalls.c:85:9: note: uninitialized use occurs here
      85 |         return head;
         |                ^~~~
   kernel/futex/syscalls.c:75:2: note: remove the 'if' if its condition is always true
      75 |         if (index >= 0) {
         |         ^~~~~~~~~~~~~~~
   kernel/futex/syscalls.c:48:19: note: initialize the variable 'head' to silence this warning
      48 |         void __user *head;
         |                          ^
         |                           = NULL
   1 warning generated.


vim +75 kernel/futex/syscalls.c

af8cc9600bbf22 Peter Zijlstra 2021-09-23  44  
5588aabbe40841 André Almeida  2026-11-15  45  static void __user *futex_get_robust_list_common(int pid, bool compat, int index)
6b54082c3ed4dc Pranav Tyagi   2025-09-15  46  {
6b54082c3ed4dc Pranav Tyagi   2025-09-15  47  	struct task_struct *p = current;
6b54082c3ed4dc Pranav Tyagi   2025-09-15  48  	void __user *head;
6b54082c3ed4dc Pranav Tyagi   2025-09-15  49  	int ret;
af8cc9600bbf22 Peter Zijlstra 2021-09-23  50  
a2d2b7acb53d36 André Almeida  2026-11-15  51  	if (index >= FUTEX_ROBUST_LIST2_MAX_IDX)
a2d2b7acb53d36 André Almeida  2026-11-15  52  		return (void __user *)ERR_PTR(-EINVAL);
a2d2b7acb53d36 André Almeida  2026-11-15  53  
6b54082c3ed4dc Pranav Tyagi   2025-09-15  54  	scoped_guard(rcu) {
6b54082c3ed4dc Pranav Tyagi   2025-09-15  55  		if (pid) {
af8cc9600bbf22 Peter Zijlstra 2021-09-23  56  			p = find_task_by_vpid(pid);
af8cc9600bbf22 Peter Zijlstra 2021-09-23  57  			if (!p)
6b54082c3ed4dc Pranav Tyagi   2025-09-15  58  				return (void __user *)ERR_PTR(-ESRCH);
6b54082c3ed4dc Pranav Tyagi   2025-09-15  59  		}
6b54082c3ed4dc Pranav Tyagi   2025-09-15  60  		get_task_struct(p);
af8cc9600bbf22 Peter Zijlstra 2021-09-23  61  	}
af8cc9600bbf22 Peter Zijlstra 2021-09-23  62  
6b54082c3ed4dc Pranav Tyagi   2025-09-15  63  	/*
6b54082c3ed4dc Pranav Tyagi   2025-09-15  64  	 * Hold exec_update_lock to serialize with concurrent exec()
6b54082c3ed4dc Pranav Tyagi   2025-09-15  65  	 * so ptrace_may_access() is checked against stable credentials
6b54082c3ed4dc Pranav Tyagi   2025-09-15  66  	 */
6b54082c3ed4dc Pranav Tyagi   2025-09-15  67  	ret = down_read_killable(&p->signal->exec_update_lock);
6b54082c3ed4dc Pranav Tyagi   2025-09-15  68  	if (ret)
6b54082c3ed4dc Pranav Tyagi   2025-09-15  69  		goto err_put;
6b54082c3ed4dc Pranav Tyagi   2025-09-15  70  
af8cc9600bbf22 Peter Zijlstra 2021-09-23  71  	ret = -EPERM;
af8cc9600bbf22 Peter Zijlstra 2021-09-23  72  	if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
af8cc9600bbf22 Peter Zijlstra 2021-09-23  73  		goto err_unlock;
af8cc9600bbf22 Peter Zijlstra 2021-09-23  74  
5588aabbe40841 André Almeida  2026-11-15 @75  	if (index >= 0) {
5588aabbe40841 André Almeida  2026-11-15  76  		scoped_guard(mutex, &p->futex.exit_mutex) {
5588aabbe40841 André Almeida  2026-11-15  77  			uintptr_t *rl = p->futex.robust_lists;
5588aabbe40841 André Almeida  2026-11-15  78  			head = rl ? (void __user *) rl[index] : NULL;
5588aabbe40841 André Almeida  2026-11-15  79  		}
5588aabbe40841 André Almeida  2026-11-15  80  	}
af8cc9600bbf22 Peter Zijlstra 2021-09-23  81  
6b54082c3ed4dc Pranav Tyagi   2025-09-15  82  	up_read(&p->signal->exec_update_lock);
6b54082c3ed4dc Pranav Tyagi   2025-09-15  83  	put_task_struct(p);
6b54082c3ed4dc Pranav Tyagi   2025-09-15  84  
6b54082c3ed4dc Pranav Tyagi   2025-09-15  85  	return head;
af8cc9600bbf22 Peter Zijlstra 2021-09-23  86  
af8cc9600bbf22 Peter Zijlstra 2021-09-23  87  err_unlock:
6b54082c3ed4dc Pranav Tyagi   2025-09-15  88  	up_read(&p->signal->exec_update_lock);
6b54082c3ed4dc Pranav Tyagi   2025-09-15  89  err_put:
6b54082c3ed4dc Pranav Tyagi   2025-09-15  90  	put_task_struct(p);
6b54082c3ed4dc Pranav Tyagi   2025-09-15  91  	return (void __user *)ERR_PTR(ret);
6b54082c3ed4dc Pranav Tyagi   2025-09-15  92  }
af8cc9600bbf22 Peter Zijlstra 2021-09-23  93  

--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki