Re: [PATCH 3/5] mm: shrinkers: make count and scan in shrinker debugfs lockless

Re: [PATCH 3/5] mm: shrinkers: make count and scan in shrinker debugfs lockless

[kernel test robot]

Hi Qi,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on akpm-mm/mm-everything]
[also build test WARNING on next-20230220]
[cannot apply to device-mapper-dm/for-next linus/master v6.2]
[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/Qi-Zheng/mm-vmscan-make-global-slab-shrink-lockless/20230220-171954
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20230220091637.64865-4-zhengqi.arch%40bytedance.com
patch subject: [PATCH 3/5] mm: shrinkers: make count and scan in shrinker debugfs lockless
config: riscv-randconfig-r036-20230219 (https://download.01.org/0day-ci/archive/20230220/202302202134.OFjSh3rl-lkp@intel.com/config)
compiler: clang version 17.0.0 (https://github.com/llvm/llvm-project db89896bbbd2251fff457699635acbbedeead27f)
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
        # install riscv cross compiling tool for clang build
        # apt-get install binutils-riscv64-linux-gnu
        # https://github.com/intel-lab-lkp/linux/commit/b5b7259339a7a5cfae5a120356750c5a9e151d12
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Qi-Zheng/mm-vmscan-make-global-slab-shrink-lockless/20230220-171954
        git checkout b5b7259339a7a5cfae5a120356750c5a9e151d12
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=riscv olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=riscv SHELL=/bin/bash

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>
| Link: https://lore.kernel.org/oe-kbuild-all/202302202134.OFjSh3rl-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> mm/shrinker_debug.c:88:11: warning: variable 'ret' is used uninitialized whenever 'do' loop exits because its condition is false [-Wsometimes-uninitialized]
           } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   mm/shrinker_debug.c:93:9: note: uninitialized use occurs here
           return ret;
                  ^~~
   mm/shrinker_debug.c:88:11: note: remove the condition if it is always true
           } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                    1
>> mm/shrinker_debug.c:78:7: warning: variable 'ret' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
                   if (!memcg_aware) {
                       ^~~~~~~~~~~~
   mm/shrinker_debug.c:93:9: note: uninitialized use occurs here
           return ret;
                  ^~~
   mm/shrinker_debug.c:78:3: note: remove the 'if' if its condition is always false
                   if (!memcg_aware) {
                   ^~~~~~~~~~~~~~~~~~~
   mm/shrinker_debug.c:53:9: note: initialize the variable 'ret' to silence this warning
           int ret, nid, srcu_idx;
                  ^
                   = 0
   2 warnings generated.


vim +88 mm/shrinker_debug.c

5035ebc644aec9 Roman Gushchin 2022-05-31  45  
5035ebc644aec9 Roman Gushchin 2022-05-31  46  static int shrinker_debugfs_count_show(struct seq_file *m, void *v)
5035ebc644aec9 Roman Gushchin 2022-05-31  47  {
5035ebc644aec9 Roman Gushchin 2022-05-31  48  	struct shrinker *shrinker = m->private;
5035ebc644aec9 Roman Gushchin 2022-05-31  49  	unsigned long *count_per_node;
5035ebc644aec9 Roman Gushchin 2022-05-31  50  	struct mem_cgroup *memcg;
5035ebc644aec9 Roman Gushchin 2022-05-31  51  	unsigned long total;
5035ebc644aec9 Roman Gushchin 2022-05-31  52  	bool memcg_aware;
b5b7259339a7a5 Qi Zheng       2023-02-20  53  	int ret, nid, srcu_idx;
5035ebc644aec9 Roman Gushchin 2022-05-31  54  
5035ebc644aec9 Roman Gushchin 2022-05-31  55  	count_per_node = kcalloc(nr_node_ids, sizeof(unsigned long), GFP_KERNEL);
5035ebc644aec9 Roman Gushchin 2022-05-31  56  	if (!count_per_node)
5035ebc644aec9 Roman Gushchin 2022-05-31  57  		return -ENOMEM;
5035ebc644aec9 Roman Gushchin 2022-05-31  58  
b5b7259339a7a5 Qi Zheng       2023-02-20  59  	srcu_idx = srcu_read_lock(&shrinker_srcu);
5035ebc644aec9 Roman Gushchin 2022-05-31  60  
5035ebc644aec9 Roman Gushchin 2022-05-31  61  	memcg_aware = shrinker->flags & SHRINKER_MEMCG_AWARE;
5035ebc644aec9 Roman Gushchin 2022-05-31  62  
5035ebc644aec9 Roman Gushchin 2022-05-31  63  	memcg = mem_cgroup_iter(NULL, NULL, NULL);
5035ebc644aec9 Roman Gushchin 2022-05-31  64  	do {
5035ebc644aec9 Roman Gushchin 2022-05-31  65  		if (memcg && !mem_cgroup_online(memcg))
5035ebc644aec9 Roman Gushchin 2022-05-31  66  			continue;
5035ebc644aec9 Roman Gushchin 2022-05-31  67  
5035ebc644aec9 Roman Gushchin 2022-05-31  68  		total = shrinker_count_objects(shrinker,
5035ebc644aec9 Roman Gushchin 2022-05-31  69  					       memcg_aware ? memcg : NULL,
5035ebc644aec9 Roman Gushchin 2022-05-31  70  					       count_per_node);
5035ebc644aec9 Roman Gushchin 2022-05-31  71  		if (total) {
5035ebc644aec9 Roman Gushchin 2022-05-31  72  			seq_printf(m, "%lu", mem_cgroup_ino(memcg));
5035ebc644aec9 Roman Gushchin 2022-05-31  73  			for_each_node(nid)
5035ebc644aec9 Roman Gushchin 2022-05-31  74  				seq_printf(m, " %lu", count_per_node[nid]);
5035ebc644aec9 Roman Gushchin 2022-05-31  75  			seq_putc(m, '\n');
5035ebc644aec9 Roman Gushchin 2022-05-31  76  		}
5035ebc644aec9 Roman Gushchin 2022-05-31  77  
5035ebc644aec9 Roman Gushchin 2022-05-31 @78  		if (!memcg_aware) {
5035ebc644aec9 Roman Gushchin 2022-05-31  79  			mem_cgroup_iter_break(NULL, memcg);
5035ebc644aec9 Roman Gushchin 2022-05-31  80  			break;
5035ebc644aec9 Roman Gushchin 2022-05-31  81  		}
5035ebc644aec9 Roman Gushchin 2022-05-31  82  
5035ebc644aec9 Roman Gushchin 2022-05-31  83  		if (signal_pending(current)) {
5035ebc644aec9 Roman Gushchin 2022-05-31  84  			mem_cgroup_iter_break(NULL, memcg);
5035ebc644aec9 Roman Gushchin 2022-05-31  85  			ret = -EINTR;
5035ebc644aec9 Roman Gushchin 2022-05-31  86  			break;
5035ebc644aec9 Roman Gushchin 2022-05-31  87  		}
5035ebc644aec9 Roman Gushchin 2022-05-31 @88  	} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
5035ebc644aec9 Roman Gushchin 2022-05-31  89  
b5b7259339a7a5 Qi Zheng       2023-02-20  90  	srcu_read_unlock(&shrinker_srcu, srcu_idx);
5035ebc644aec9 Roman Gushchin 2022-05-31  91  
5035ebc644aec9 Roman Gushchin 2022-05-31  92  	kfree(count_per_node);
5035ebc644aec9 Roman Gushchin 2022-05-31 @93  	return ret;
5035ebc644aec9 Roman Gushchin 2022-05-31  94  }
5035ebc644aec9 Roman Gushchin 2022-05-31  95  DEFINE_SHOW_ATTRIBUTE(shrinker_debugfs_count);
5035ebc644aec9 Roman Gushchin 2022-05-31  96  

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