Hi Yi,

[FYI, it's a private test report for your RFC patch.]
[auto build test ERROR on driver-core/driver-core-testing]
[also build test ERROR on linus/master next-20210908]
[cannot apply to cgroup/for-next kees/for-next/pstore v5.14]
[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]

url:    https://github.com/0day-ci/linux/commits/Yi-Tao/support-cgroup-pool-in-v1/20210908-201642
base:   https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core.git 4b93c544e90e2b28326182d31ee008eb80e02074
config: m68k-randconfig-r014-20210908 (attached as .config)
compiler: m68k-linux-gcc (GCC) 11.2.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/0day-ci/linux/commit/6fadbb12de926d6d4fd6d903304d5cbe52bbbc52
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Yi-Tao/support-cgroup-pool-in-v1/20210908-201642
        git checkout 6fadbb12de926d6d4fd6d903304d5cbe52bbbc52
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross ARCH=m68k 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   kernel/cgroup/cgroup.c: In function 'cgroup_mkdir':
>> kernel/cgroup/cgroup.c:5513:29: error: unused variable 'kn' [-Werror=unused-variable]
    5513 |         struct kernfs_node *kn;
         |                             ^~
   cc1: all warnings being treated as errors


vim +/kn +5513 kernel/cgroup/cgroup.c

  5509	
  5510	int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name, umode_t mode)
  5511	{
  5512		struct cgroup *parent, *cgrp;
> 5513		struct kernfs_node *kn;
  5514		int ret = 1;
  5515		bool hide = false;
  5516	
  5517		/* do not accept '\n' to prevent making /proc/<pid>/cgroup unparsable */
  5518		if (strchr(name, '\n'))
  5519			return -EINVAL;
  5520	
  5521		/* 0xffff means cgroup is created for pool, set to default mode 0x1ed */
  5522		if (mode == 0xffff) {
  5523			hide = true;
  5524			mode = 0x1ed;
  5525		}
  5526	
  5527		if (!hide)
  5528			ret = cgroup_mkdir_fast_path(parent_kn, name);
  5529		if (ret <= 0)
  5530			return ret;
  5531	
  5532		parent = cgroup_kn_lock_live(parent_kn, false);
  5533		if (!parent)
  5534			return -ENODEV;
  5535	
  5536		if (!cgroup_check_hierarchy_limits(parent)) {
  5537			ret = -EAGAIN;
  5538			goto out_unlock;
  5539		}
  5540	
  5541		cgrp = cgroup_create(parent, name, mode);
  5542		if (IS_ERR(cgrp)) {
  5543			ret = PTR_ERR(cgrp);
  5544			goto out_unlock;
  5545		}
  5546	
  5547		/*
  5548		 * This extra ref will be put in cgroup_free_fn() and guarantees
  5549		 * that @cgrp->kn is always accessible.
  5550		 */
  5551		kernfs_get(cgrp->kn);
  5552	
  5553		ret = cgroup_kn_set_ugid(cgrp->kn);
  5554		if (ret)
  5555			goto out_destroy;
  5556	
  5557		ret = css_populate_dir(&cgrp->self);
  5558		if (ret)
  5559			goto out_destroy;
  5560	
  5561		ret = cgroup_apply_control_enable(cgrp);
  5562		if (ret)
  5563			goto out_destroy;
  5564	
  5565		TRACE_CGROUP_PATH(mkdir, cgrp);
  5566	
  5567		/* let's create and online css's */
  5568		kernfs_activate(cgrp->kn);
  5569	
  5570		if (hide)
  5571			cgroup_hide(parent, cgrp, name);
  5572	
  5573		ret = 0;
  5574		goto out_unlock;
  5575	
  5576	out_destroy:
  5577		cgroup_destroy_locked(cgrp);
  5578	out_unlock:
  5579		cgroup_kn_unlock(parent_kn);
  5580		return ret;
  5581	}
  5582	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all(a)lists.01.org