Re: [PATCH v3 2/2] blk-cgroup: Optimize blkcg_rstat_flush()

kernel test robot
2022-06-02T06:33:21Z

Hi Waiman,

I love your patch! Perhaps something to improve:

[auto build test WARNING on axboe-block/for-next]
[also build test WARNING on linus/master next-20220601]
[cannot apply to v5.18]
[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/intel-lab-lkp/linux/commits/Waiman-Long/blk-cgroup-Optimize-blkcg_rstat_flush/20220602-052441
base: https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git for-next
config: x86_64-randconfig-a012 (https://download.01.org/0day-ci/archive/20220602/202206021418.wpJNbe3g-lkp@intel.com/config)
compiler: clang version 15.0.0 (https://github.com/llvm/llvm-project c825abd6b0198fb088d9752f556a70705bc99dfd)
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/intel-lab-lkp/linux/commit/3f979cef411e5d5512b725753034b02f3b7baf44
git remote add linux-review https://github.com/intel-lab-lkp/linux
git fetch --no-tags linux-review Waiman-Long/blk-cgroup-Optimize-blkcg_rstat_flush/20220602-052441
git checkout 3f979cef411e5d5512b725753034b02f3b7baf44
# 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=x86_64 SHELL=/bin/bash

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

All warnings (new ones prefixed by >>):

>> block/blk-cgroup.c:1255:6: warning: variable 'ret' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
if (!blkcg->lhead)
^~~~~~~~~~~~~
block/blk-cgroup.c:1306:9: note: uninitialized use occurs here
return ret;
^~~
block/blk-cgroup.c:1255:2: note: remove the 'if' if its condition is always false
if (!blkcg->lhead)
^~~~~~~~~~~~~~~~~~
block/blk-cgroup.c:1239:33: note: initialize the variable 'ret' to silence this warning
struct cgroup_subsys_state *ret;
^
= NULL
1 warning generated.

vim +1255 block/blk-cgroup.c

1234
1235 static struct cgroup_subsys_state *
1236 blkcg_css_alloc(struct cgroup_subsys_state *parent_css)
1237 {
1238 struct blkcg *blkcg;
1239 struct cgroup_subsys_state *ret;
1240 int i;
1241
1242 mutex_lock(&blkcg_pol_mutex);
1243
1244 if (!parent_css) {
1245 blkcg = &blkcg_root;
1246 } else {
1247 blkcg = kzalloc(sizeof(*blkcg), GFP_KERNEL);
1248 if (!blkcg) {
1249 ret = ERR_PTR(-ENOMEM);
1250 goto unlock;
1251 }
1252 }
1253
1254 blkcg->lhead = alloc_percpu_gfp(struct llist_head, GFP_KERNEL);
> 1255 if (!blkcg->lhead)
1256 goto free_blkcg;
1257 init_blkcg_llists(blkcg);
1258
1259 for (i = 0; i < BLKCG_MAX_POLS ; i++) {
1260 struct blkcg_policy *pol = blkcg_policy[i];
1261 struct blkcg_policy_data *cpd;
1262
1263 /*
1264 * If the policy hasn't been attached yet, wait for it
1265 * to be attached before doing anything else. Otherwise,
1266 * check if the policy requires any specific per-cgroup
1267 * data: if it does, allocate and initialize it.
1268 */
1269 if (!pol || !pol->cpd_alloc_fn)
1270 continue;
1271
1272 cpd = pol->cpd_alloc_fn(GFP_KERNEL);
1273 if (!cpd) {
1274 ret = ERR_PTR(-ENOMEM);
1275 goto free_pd_blkcg;
1276 }
1277 blkcg->cpd[i] = cpd;
1278 cpd->blkcg = blkcg;
1279 cpd->plid = i;
1280 if (pol->cpd_init_fn)
1281 pol->cpd_init_fn(cpd);
1282 }
1283
1284 spin_lock_init(&blkcg->lock);
1285 refcount_set(&blkcg->online_pin, 1);
1286 INIT_RADIX_TREE(&blkcg->blkg_tree, GFP_NOWAIT | __GFP_NOWARN);
1287 INIT_HLIST_HEAD(&blkcg->blkg_list);
1288 #ifdef CONFIG_CGROUP_WRITEBACK
1289 INIT_LIST_HEAD(&blkcg->cgwb_list);
1290 #endif
1291 list_add_tail(&blkcg->all_blkcgs_node, &all_blkcgs);
1292
1293 mutex_unlock(&blkcg_pol_mutex);
1294 return &blkcg->css;
1295
1296 free_pd_blkcg:
1297 for (i--; i >= 0; i--)
1298 if (blkcg->cpd[i])
1299 blkcg_policy[i]->cpd_free_fn(blkcg->cpd[i]);
1300 free_percpu(blkcg->lhead);
1301 free_blkcg:
1302 if (blkcg != &blkcg_root)
1303 kfree(blkcg);
1304 unlock:
1305 mutex_unlock(&blkcg_pol_mutex);
1306 return ret;
1307 }
1308

--
0-DAY CI Kernel Test Service