Re: [PATCHv2] sched/deadline: Walk up cpuset hierarchy to decide root domain when hot-unplug

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

Hi Pingfan,

kernel test robot noticed the following build warnings:

[auto build test WARNING on tj-cgroup/for-next]
[also build test WARNING on tip/sched/core tip/master linus/master v6.18-rc1 next-20251016]
[cannot apply to tip/auto-latest]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Pingfan-Liu/sched-deadline-Walk-up-cpuset-hierarchy-to-decide-root-domain-when-hot-unplug/20251016-200452
base:   https://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git for-next
patch link:    https://lore.kernel.org/r/20251016120041.17990-1-piliu%40redhat.com
patch subject: [PATCHv2] sched/deadline: Walk up cpuset hierarchy to decide root domain when hot-unplug
config: openrisc-allnoconfig (https://download.01.org/0day-ci/archive/20251017/202510171039.kkg2ItuG-lkp@intel.com/config)
compiler: or1k-linux-gcc (GCC) 15.1.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251017/202510171039.kkg2ItuG-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/202510171039.kkg2ItuG-lkp@intel.com/

All warnings (new ones prefixed by >>):

   In file included from include/linux/smp.h:13,
                    from include/linux/lockdep.h:14,
                    from include/linux/spinlock.h:63,
                    from include/linux/mmzone.h:8,
                    from include/linux/gfp.h:7,
                    from include/linux/umh.h:4,
                    from include/linux/kmod.h:9,
                    from include/linux/module.h:18,
                    from init/main.c:18:
   include/linux/cpuset.h: In function 'cpuset_task_rd_effective_cpus':
>> include/linux/cpumask.h:125:28: warning: return discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
     125 | #define cpu_active_mask   ((const struct cpumask *)&__cpu_active_mask)
         |                           ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/cpuset.h:282:16: note: in expansion of macro 'cpu_active_mask'
     282 |         return cpu_active_mask;
         |                ^~~~~~~~~~~~~~~


vim +/const +125 include/linux/cpumask.h

^1da177e4c3f415 Linus Torvalds   2005-04-16   77  
^1da177e4c3f415 Linus Torvalds   2005-04-16   78  /*
^1da177e4c3f415 Linus Torvalds   2005-04-16   79   * The following particular system cpumasks and operations manage
b3199c025d1646e Rusty Russell    2008-12-30   80   * possible, present, active and online cpus.
^1da177e4c3f415 Linus Torvalds   2005-04-16   81   *
b3199c025d1646e Rusty Russell    2008-12-30   82   *     cpu_possible_mask- has bit 'cpu' set iff cpu is populatable
b3199c025d1646e Rusty Russell    2008-12-30   83   *     cpu_present_mask - has bit 'cpu' set iff cpu is populated
4e1a7df4548003f James Morse      2024-05-29   84   *     cpu_enabled_mask - has bit 'cpu' set iff cpu can be brought online
b3199c025d1646e Rusty Russell    2008-12-30   85   *     cpu_online_mask  - has bit 'cpu' set iff cpu available to scheduler
b3199c025d1646e Rusty Russell    2008-12-30   86   *     cpu_active_mask  - has bit 'cpu' set iff cpu available to migration
^1da177e4c3f415 Linus Torvalds   2005-04-16   87   *
b3199c025d1646e Rusty Russell    2008-12-30   88   *  If !CONFIG_HOTPLUG_CPU, present == possible, and active == online.
^1da177e4c3f415 Linus Torvalds   2005-04-16   89   *
57f728d59f005df Randy Dunlap     2023-07-31   90   *  The cpu_possible_mask is fixed at boot time, as the set of CPU IDs
b3199c025d1646e Rusty Russell    2008-12-30   91   *  that it is possible might ever be plugged in at anytime during the
b3199c025d1646e Rusty Russell    2008-12-30   92   *  life of that system boot.  The cpu_present_mask is dynamic(*),
b3199c025d1646e Rusty Russell    2008-12-30   93   *  representing which CPUs are currently plugged in.  And
b3199c025d1646e Rusty Russell    2008-12-30   94   *  cpu_online_mask is the dynamic subset of cpu_present_mask,
b3199c025d1646e Rusty Russell    2008-12-30   95   *  indicating those CPUs available for scheduling.
b3199c025d1646e Rusty Russell    2008-12-30   96   *
b3199c025d1646e Rusty Russell    2008-12-30   97   *  If HOTPLUG is enabled, then cpu_present_mask varies dynamically,
^1da177e4c3f415 Linus Torvalds   2005-04-16   98   *  depending on what ACPI reports as currently plugged in, otherwise
b3199c025d1646e Rusty Russell    2008-12-30   99   *  cpu_present_mask is just a copy of cpu_possible_mask.
^1da177e4c3f415 Linus Torvalds   2005-04-16  100   *
b3199c025d1646e Rusty Russell    2008-12-30  101   *  (*) Well, cpu_present_mask is dynamic in the hotplug case.  If not
b3199c025d1646e Rusty Russell    2008-12-30  102   *      hotplug, it's a copy of cpu_possible_mask, hence fixed at boot.
^1da177e4c3f415 Linus Torvalds   2005-04-16  103   *
^1da177e4c3f415 Linus Torvalds   2005-04-16  104   * Subtleties:
57f728d59f005df Randy Dunlap     2023-07-31  105   * 1) UP ARCHes (NR_CPUS == 1, CONFIG_SMP not defined) hardcode
^1da177e4c3f415 Linus Torvalds   2005-04-16  106   *    assumption that their single CPU is online.  The UP
b3199c025d1646e Rusty Russell    2008-12-30  107   *    cpu_{online,possible,present}_masks are placebos.  Changing them
^1da177e4c3f415 Linus Torvalds   2005-04-16  108   *    will have no useful affect on the following num_*_cpus()
^1da177e4c3f415 Linus Torvalds   2005-04-16  109   *    and cpu_*() macros in the UP case.  This ugliness is a UP
^1da177e4c3f415 Linus Torvalds   2005-04-16  110   *    optimization - don't waste any instructions or memory references
^1da177e4c3f415 Linus Torvalds   2005-04-16  111   *    asking if you're online or how many CPUs there are if there is
^1da177e4c3f415 Linus Torvalds   2005-04-16  112   *    only one CPU.
^1da177e4c3f415 Linus Torvalds   2005-04-16  113   */
^1da177e4c3f415 Linus Torvalds   2005-04-16  114  
4b804c85dc37db6 Rasmus Villemoes 2016-01-20  115  extern struct cpumask __cpu_possible_mask;
4b804c85dc37db6 Rasmus Villemoes 2016-01-20  116  extern struct cpumask __cpu_online_mask;
4e1a7df4548003f James Morse      2024-05-29  117  extern struct cpumask __cpu_enabled_mask;
4b804c85dc37db6 Rasmus Villemoes 2016-01-20  118  extern struct cpumask __cpu_present_mask;
4b804c85dc37db6 Rasmus Villemoes 2016-01-20  119  extern struct cpumask __cpu_active_mask;
e40f74c535b8a0e Peter Zijlstra   2021-01-19  120  extern struct cpumask __cpu_dying_mask;
5aec01b834fd6f8 Rasmus Villemoes 2016-01-20  121  #define cpu_possible_mask ((const struct cpumask *)&__cpu_possible_mask)
5aec01b834fd6f8 Rasmus Villemoes 2016-01-20  122  #define cpu_online_mask   ((const struct cpumask *)&__cpu_online_mask)
4e1a7df4548003f James Morse      2024-05-29  123  #define cpu_enabled_mask   ((const struct cpumask *)&__cpu_enabled_mask)
5aec01b834fd6f8 Rasmus Villemoes 2016-01-20  124  #define cpu_present_mask  ((const struct cpumask *)&__cpu_present_mask)
5aec01b834fd6f8 Rasmus Villemoes 2016-01-20 @125  #define cpu_active_mask   ((const struct cpumask *)&__cpu_active_mask)
e40f74c535b8a0e Peter Zijlstra   2021-01-19  126  #define cpu_dying_mask    ((const struct cpumask *)&__cpu_dying_mask)
b3199c025d1646e Rusty Russell    2008-12-30  127  

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