Re: [PATCH] cgroup: Defer css percpu_ref kill on rmdir until cgroup is depopulated

[kernel test robot]

Hi Tejun,

kernel test robot noticed the following build errors:

[auto build test ERROR on tj-cgroup/for-next]
[also build test ERROR on linus/master next-20260430]
[cannot apply to v7.1-rc1]
[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/Tejun-Heo/cgroup-Defer-css-percpu_ref-kill-on-rmdir-until-cgroup-is-depopulated/20260503-165802
base:   https://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git for-next
patch link:    https://lore.kernel.org/r/20260501022943.3714461-1-tj%40kernel.org
patch subject: [PATCH] cgroup: Defer css percpu_ref kill on rmdir until cgroup is depopulated
config: m68k-allmodconfig (https://download.01.org/0day-ci/archive/20260504/202605040655.KI0GsBVb-lkp@xxxxxxxxx/config)
compiler: m68k-linux-gcc (GCC) 15.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260504/202605040655.KI0GsBVb-lkp@xxxxxxxxx/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@xxxxxxxxx>
| Closes: https://lore.kernel.org/oe-kbuild-all/202605040655.KI0GsBVb-lkp@xxxxxxxxx/

All errors (new ones prefixed by >>):

   kernel/cgroup/cgroup.c: In function 'cgroup_apply_control_disable':
>> kernel/cgroup/cgroup.c:3391:33: error: implicit declaration of function 'kill_css_sync'; did you mean 'kill_fasync'? [-Wimplicit-function-declaration]
    3391 |                                 kill_css_sync(css);
         |                                 ^~~~~~~~~~~~~
         |                                 kill_fasync
>> kernel/cgroup/cgroup.c:3392:33: error: implicit declaration of function 'kill_css_finish' [-Wimplicit-function-declaration]
    3392 |                                 kill_css_finish(css);
         |                                 ^~~~~~~~~~~~~~~
   kernel/cgroup/cgroup.c: At top level:
   kernel/cgroup/cgroup.c:6047:13: warning: conflicting types for 'kill_css_sync'; have 'void(struct cgroup_subsys_state *)'
    6047 | static void kill_css_sync(struct cgroup_subsys_state *css)
         |             ^~~~~~~~~~~~~
>> kernel/cgroup/cgroup.c:6047:13: error: static declaration of 'kill_css_sync' follows non-static declaration
   kernel/cgroup/cgroup.c:3391:33: note: previous implicit declaration of 'kill_css_sync' with type 'void(struct cgroup_subsys_state *)'
    3391 |                                 kill_css_sync(css);
         |                                 ^~~~~~~~~~~~~
   kernel/cgroup/cgroup.c:6087:13: warning: conflicting types for 'kill_css_finish'; have 'void(struct cgroup_subsys_state *)'
    6087 | static void kill_css_finish(struct cgroup_subsys_state *css)
         |             ^~~~~~~~~~~~~~~
>> kernel/cgroup/cgroup.c:6087:13: error: static declaration of 'kill_css_finish' follows non-static declaration
   kernel/cgroup/cgroup.c:3392:33: note: previous implicit declaration of 'kill_css_finish' with type 'void(struct cgroup_subsys_state *)'
    3392 |                                 kill_css_finish(css);
         |                                 ^~~~~~~~~~~~~~~


vim +3391 kernel/cgroup/cgroup.c

  3359	
  3360	/**
  3361	 * cgroup_apply_control_disable - kill or hide csses according to control
  3362	 * @cgrp: root of the target subtree
  3363	 *
  3364	 * Walk @cgrp's subtree and kill and hide csses so that they match
  3365	 * cgroup_ss_mask() and cgroup_visible_mask().
  3366	 *
  3367	 * A css is hidden when the userland requests it to be disabled while other
  3368	 * subsystems are still depending on it.  The css must not actively control
  3369	 * resources and be in the vanilla state if it's made visible again later.
  3370	 * Controllers which may be depended upon should provide ->css_reset() for
  3371	 * this purpose.
  3372	 */
  3373	static void cgroup_apply_control_disable(struct cgroup *cgrp)
  3374	{
  3375		struct cgroup *dsct;
  3376		struct cgroup_subsys_state *d_css;
  3377		struct cgroup_subsys *ss;
  3378		int ssid;
  3379	
  3380		cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
  3381			for_each_subsys(ss, ssid) {
  3382				struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
  3383	
  3384				if (!css)
  3385					continue;
  3386	
  3387				WARN_ON_ONCE(percpu_ref_is_dying(&css->refcnt));
  3388	
  3389				if (css->parent &&
  3390				    !(cgroup_ss_mask(dsct) & (1 << ss->id))) {
> 3391					kill_css_sync(css);
> 3392					kill_css_finish(css);
  3393				} else if (!css_visible(css)) {
  3394					css_clear_dir(css);
  3395					if (ss->css_reset)
  3396						ss->css_reset(css);
  3397				}
  3398			}
  3399		}
  3400	}
  3401	

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