Re: [PATCH -next 1/3] cgroup/dmem: fix NULL pointer dereference when setting max

[kernel test robot <lkp@intel.com>]

Hi Chen,

kernel test robot noticed the following build warnings:

[auto build test WARNING on next-20260130]

url:    https://github.com/intel-lab-lkp/linux/commits/Chen-Ridong/cgroup-dmem-fix-NULL-pointer-dereference-when-setting-max/20260131-173002
base:   next-20260130
patch link:    https://lore.kernel.org/r/20260131091202.344788-2-chenridong%40huaweicloud.com
patch subject: [PATCH -next 1/3] cgroup/dmem: fix NULL pointer dereference when setting max
config: x86_64-randconfig-161-20260131 (https://download.01.org/0day-ci/archive/20260201/202602010100.5CjcoPFh-lkp@intel.com/config)
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
smatch version: v0.5.0-8994-gd50c5a4c
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260201/202602010100.5CjcoPFh-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/202602010100.5CjcoPFh-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> kernel/cgroup/dmem.c:703:7: warning: variable 'region' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
     703 |                 if (!options || !*options) {
         |                     ^~~~~~~~~~~~~~~~~~~~~
   kernel/cgroup/dmem.c:729:13: note: uninitialized use occurs here
     729 |                 kref_put(&region->ref, dmemcg_free_region);
         |                           ^~~~~~
   kernel/cgroup/dmem.c:703:3: note: remove the 'if' if its condition is always false
     703 |                 if (!options || !*options) {
         |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
     704 |                         err = -EINVAL;
         |                         ~~~~~~~~~~~~~~
     705 |                         goto out_put;
         |                         ~~~~~~~~~~~~~
     706 |                 }
         |                 ~
>> kernel/cgroup/dmem.c:703:7: warning: variable 'region' is used uninitialized whenever '||' condition is true [-Wsometimes-uninitialized]
     703 |                 if (!options || !*options) {
         |                     ^~~~~~~~
   kernel/cgroup/dmem.c:729:13: note: uninitialized use occurs here
     729 |                 kref_put(&region->ref, dmemcg_free_region);
         |                           ^~~~~~
   kernel/cgroup/dmem.c:703:7: note: remove the '||' if its condition is always false
     703 |                 if (!options || !*options) {
         |                     ^~~~~~~~~~~
   kernel/cgroup/dmem.c:685:36: note: initialize the variable 'region' to silence this warning
     685 |                 struct dmem_cgroup_region *region;
         |                                                  ^
         |                                                   = NULL
   2 warnings generated.


vim +703 kernel/cgroup/dmem.c

   674	
   675	static ssize_t dmemcg_limit_write(struct kernfs_open_file *of,
   676					 char *buf, size_t nbytes, loff_t off,
   677					 void (*apply)(struct dmem_cgroup_pool_state *, u64))
   678	{
   679		struct dmemcg_state *dmemcs = css_to_dmemcs(of_css(of));
   680		int err = 0;
   681	
   682		while (buf && !err) {
   683			struct dmem_cgroup_pool_state *pool = NULL;
   684			char *options, *region_name;
   685			struct dmem_cgroup_region *region;
   686			u64 new_limit;
   687	
   688			options = buf;
   689			buf = strchr(buf, '\n');
   690			if (buf)
   691				*buf++ = '\0';
   692	
   693			options = strstrip(options);
   694	
   695			/* eat empty lines */
   696			if (!options[0])
   697				continue;
   698	
   699			region_name = strsep(&options, " \t");
   700			if (!region_name[0])
   701				continue;
   702	
 > 703			if (!options || !*options) {
   704				err = -EINVAL;
   705				goto out_put;
   706			}
   707	
   708			rcu_read_lock();
   709			region = dmemcg_get_region_by_name(region_name);
   710			rcu_read_unlock();
   711	
   712			if (!region)
   713				return -EINVAL;
   714	
   715			err = dmemcg_parse_limit(options, region, &new_limit);
   716			if (err < 0)
   717				goto out_put;
   718	
   719			pool = get_cg_pool_unlocked(dmemcs, region);
   720			if (IS_ERR(pool)) {
   721				err = PTR_ERR(pool);
   722				goto out_put;
   723			}
   724	
   725			/* And commit */
   726			apply(pool, new_limit);
   727	
   728	out_put:
   729			kref_put(&region->ref, dmemcg_free_region);
   730		}
   731	
   732	
   733		return err ?: nbytes;
   734	}
   735	

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