kernel/cgroup/cgroup.c:3391:5: error: call to undeclared function 'kill_css_sync'; ISO C99 and later do not support implicit function declarations

kernel/cgroup/cgroup.c:3391:5: error: call to undeclared function 'kill_css_sync'; ISO C99 and later do not support implicit function declarations

[kernel test robot]

tree:   https://github.com/intel-lab-lkp/linux/commits/Tejun-Heo/cgroup-Defer-css-percpu_ref-kill-on-rmdir-until-cgroup-is-depopulated/20260503-165802
head:   f18fcea709e431e32f29d553290a21173d8530f6
commit: f18fcea709e431e32f29d553290a21173d8530f6 cgroup: Defer css percpu_ref kill on rmdir until cgroup is depopulated
date:   6 hours ago
config: x86_64-kexec (https://download.01.org/0day-ci/archive/20260503/202605031603.MJK6LzJs-lkp@intel.com/config)
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260503/202605031603.MJK6LzJs-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/202605031603.MJK6LzJs-lkp@intel.com/

All errors (new ones prefixed by >>):

>> kernel/cgroup/cgroup.c:3391:5: error: call to undeclared function 'kill_css_sync'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
    3391 |                                 kill_css_sync(css);
         |                                 ^
   kernel/cgroup/cgroup.c:3391:5: note: did you mean 'kill_fasync'?
   include/linux/fs.h:1391:13: note: 'kill_fasync' declared here
    1391 | extern void kill_fasync(struct fasync_struct **, int, int);
         |             ^
>> kernel/cgroup/cgroup.c:3392:5: error: call to undeclared function 'kill_css_finish'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
    3392 |                                 kill_css_finish(css);
         |                                 ^
>> kernel/cgroup/cgroup.c:6047:13: error: conflicting types for 'kill_css_sync'
    6047 | static void kill_css_sync(struct cgroup_subsys_state *css)
         |             ^
   kernel/cgroup/cgroup.c:3391:5: note: previous implicit declaration is here
    3391 |                                 kill_css_sync(css);
         |                                 ^
>> kernel/cgroup/cgroup.c:6087:13: error: conflicting types for 'kill_css_finish'
    6087 | static void kill_css_finish(struct cgroup_subsys_state *css)
         |             ^
   kernel/cgroup/cgroup.c:3392:5: note: previous implicit declaration is here
    3392 |                                 kill_css_finish(css);
         |                                 ^
   4 errors generated.


vim +/kill_css_sync +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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