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Date:   Sat, 12 Aug 2023 13:43:51 +0800
From:   kernel test robot <lkp@intel.com>
To:     Li kunyu <kunyu@nfschina.com>, tj@kernel.org,
        lizefan.x@bytedance.com, hannes@cmpxchg.org
Cc:     llvm@lists.linux.dev, oe-kbuild-all@lists.linux.dev,
        cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
        Li kunyu <kunyu@nfschina.com>
Subject: Re: [PATCH] cgroup: cgroup: =?utf-8?Q?Remo?=
 =?utf-8?B?dmUgdW5uZWNlc3Nhcnkg4oCYTlVMTOKAmQ==?= values from res
Message-ID: <202308121338.k2YdCXVR-lkp@intel.com>
References: <20230813015142.3095-1-kunyu@nfschina.com>
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In-Reply-To: <20230813015142.3095-1-kunyu@nfschina.com>
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Hi Li,

kernel test robot noticed the following build warnings:

[auto build test WARNING on tj-cgroup/for-next]
[cannot apply to linus/master v6.5-rc5 next-20230809]
[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/Li-kunyu/cgroup-cgroup-Remove-unnecessary-NULL-values-from-res/20230811-172322
base:   https://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git for-next
patch link:    https://lore.kernel.org/r/20230813015142.3095-1-kunyu%40nfschina.com
patch subject: [PATCH] cgroup: cgroup: Remove unnecessary ‘NULL’ values from res
config: x86_64-randconfig-x002-20230812 (https://download.01.org/0day-ci/archive/20230812/202308121338.k2YdCXVR-lkp@intel.com/config)
compiler: clang version 16.0.4 (https://github.com/llvm/llvm-project.git ae42196bc493ffe877a7e3dff8be32035dea4d07)
reproduce: (https://download.01.org/0day-ci/archive/20230812/202308121338.k2YdCXVR-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/202308121338.k2YdCXVR-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> kernel/cgroup/cgroup.c:1380:3: warning: variable 'res' is used uninitialized whenever 'for' loop exits because its condition is false [-Wsometimes-uninitialized]
                   list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/list.h:578:7: note: expanded from macro 'list_for_each_entry'
                &pos->member != (head);                                    \
                ^~~~~~~~~~~~~~~~~~~~~~
   kernel/cgroup/cgroup.c:1391:10: note: uninitialized use occurs here
           BUG_ON(!res);
                   ^~~
   include/asm-generic/bug.h:62:45: note: expanded from macro 'BUG_ON'
   #define BUG_ON(condition) do { if (unlikely(condition)) BUG(); } while (0)
                                               ^~~~~~~~~
   include/linux/compiler.h:78:42: note: expanded from macro 'unlikely'
   # define unlikely(x)    __builtin_expect(!!(x), 0)
                                               ^
   kernel/cgroup/cgroup.c:1380:3: note: remove the condition if it is always true
                   list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
                   ^
   include/linux/list.h:578:7: note: expanded from macro 'list_for_each_entry'
                &pos->member != (head);                                    \
                ^
   kernel/cgroup/cgroup.c:1367:20: note: initialize the variable 'res' to silence this warning
           struct cgroup *res;
                             ^
                              = NULL
   1 warning generated.


vim +1380 kernel/cgroup/cgroup.c

f2e85d574e881f kernel/cgroup.c        Tejun Heo       2014-02-11  1359  
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1360  /*
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1361   * look up cgroup associated with current task's cgroup namespace on the
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1362   * specified hierarchy
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1363   */
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1364  static struct cgroup *
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1365  current_cgns_cgroup_from_root(struct cgroup_root *root)
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1366  {
aa6f66ec5ebc27 kernel/cgroup/cgroup.c Li kunyu        2023-08-13  1367  	struct cgroup *res;
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1368  	struct css_set *cset;
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1369  
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1370  	lockdep_assert_held(&css_set_lock);
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1371  
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1372  	rcu_read_lock();
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1373  
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1374  	cset = current->nsproxy->cgroup_ns->root_cset;
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1375  	if (cset == &init_css_set) {
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1376  		res = &root->cgrp;
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1377  	} else {
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1378  		struct cgrp_cset_link *link;
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1379  
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09 @1380  		list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1381  			struct cgroup *c = link->cgrp;
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1382  
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1383  			if (c->root == root) {
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1384  				res = c;
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1385  				break;
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1386  			}
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1387  		}
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1388  	}
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1389  	rcu_read_unlock();
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1390  
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1391  	BUG_ON(!res);
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1392  	return res;
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1393  }
4f41fc59620fce kernel/cgroup.c        Serge E. Hallyn 2016-05-09  1394  

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0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki