Re: [PATCH v2 -next 3/3] cgroup/freezer: Reduce redundant propagation for cgroup_propagate_frozen

Re: [PATCH v2 -next 3/3] cgroup/freezer: Reduce redundant propagation for cgroup_propagate_frozen

[kernel test robot]

Hi Chen,

kernel test robot noticed the following build warnings:

[auto build test WARNING on next-20240911]

url:    https://github.com/intel-lab-lkp/linux/commits/Chen-Ridong/cgroup-freezer-Reduce-redundant-traversal-for-cgroup_freeze/20240912-093141
base:   next-20240911
patch link:    https://lore.kernel.org/r/20240912012037.1324165-4-chenridong%40huawei.com
patch subject: [PATCH v2 -next 3/3] cgroup/freezer: Reduce redundant propagation for cgroup_propagate_frozen
config: i386-defconfig (https://download.01.org/0day-ci/archive/20240915/202409150216.INlNatES-lkp@intel.com/config)
compiler: clang version 18.1.8 (https://github.com/llvm/llvm-project 3b5b5c1ec4a3095ab096dd780e84d7ab81f3d7ff)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240915/202409150216.INlNatES-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/202409150216.INlNatES-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> kernel/cgroup/freezer.c:46:12: warning: explicitly assigning value of variable of type 'struct cgroup *' to itself [-Wself-assign]
      46 |         for (cgrp = cgrp; cgrp; cgrp = cgroup_parent(cgrp)) {
         |              ~~~~ ^ ~~~~
   1 warning generated.


vim +46 kernel/cgroup/freezer.c

    32	
    33	/*
    34	 * Propagate the cgroup frozen state upwards by the cgroup tree.
    35	 */
    36	static void cgroup_propagate_frozen(struct cgroup *cgrp, bool frozen)
    37	{
    38		int deta;
    39		struct cgroup *parent;
    40		/*
    41		 * If the new state is frozen, some freezing ancestor cgroups may change
    42		 * their state too, depending on if all their descendants are frozen.
    43		 *
    44		 * Otherwise, all ancestor cgroups are forced into the non-frozen state.
    45		 */
  > 46		for (cgrp = cgrp; cgrp; cgrp = cgroup_parent(cgrp)) {
    47			if (frozen) {
    48				/* If freezer is not set, or cgrp has descendants
    49				 * that are not frozen, cgrp can't be frozen
    50				 */
    51				if (!test_bit(CGRP_FREEZE, &cgrp->flags) ||
    52				    (cgrp->freezer.nr_frozen_descendants !=
    53				     cgrp->nr_descendants))
    54					break;
    55				deta = cgrp->freezer.nr_frozen_descendants + 1;
    56			} else {
    57				deta = -(cgrp->freezer.nr_frozen_descendants + 1);
    58			}
    59	
    60			/* No change, stop propagate */
    61			if (!cgroup_update_frozen_flag(cgrp, frozen))
    62				break;
    63	
    64			parent = cgroup_parent(cgrp);
    65			parent->freezer.nr_frozen_descendants += deta;
    66		}
    67	}
    68	

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