[rgushchin:kmem_performance.1 4/7] mm/memcontrol.c:3016:17: sparse: sparse: Using plain integer as NULL pointer

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

tree:   https://github.com/rgushchin/linux.git kmem_performance.1
head:   4ce474b7270a507dd448b335168acb30e9fe7d46
commit: 1b638f41428889e8e7ab15b64939d9ceeeabfbd5 [4/7] mm: kmem: add direct objcg pointer to task_struct
config: x86_64-randconfig-123-20230930 (https://download.01.org/0day-ci/archive/20231001/202310011333.iSgIn8LO-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231001/202310011333.iSgIn8LO-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/202310011333.iSgIn8LO-lkp@intel.com/

sparse warnings: (new ones prefixed by >>)
>> mm/memcontrol.c:3016:17: sparse: sparse: Using plain integer as NULL pointer
   mm/memcontrol.c:3032:23: sparse: sparse: Using plain integer as NULL pointer
   mm/memcontrol.c:4242:21: sparse: sparse: incompatible types in comparison expression (different address spaces):
   mm/memcontrol.c:4242:21: sparse:    struct mem_cgroup_threshold_ary [noderef] __rcu *
   mm/memcontrol.c:4242:21: sparse:    struct mem_cgroup_threshold_ary *
   mm/memcontrol.c:4244:21: sparse: sparse: incompatible types in comparison expression (different address spaces):
   mm/memcontrol.c:4244:21: sparse:    struct mem_cgroup_threshold_ary [noderef] __rcu *
   mm/memcontrol.c:4244:21: sparse:    struct mem_cgroup_threshold_ary *
   mm/memcontrol.c:4400:9: sparse: sparse: incompatible types in comparison expression (different address spaces):
   mm/memcontrol.c:4400:9: sparse:    struct mem_cgroup_threshold_ary [noderef] __rcu *
   mm/memcontrol.c:4400:9: sparse:    struct mem_cgroup_threshold_ary *
   mm/memcontrol.c:4494:9: sparse: sparse: incompatible types in comparison expression (different address spaces):
   mm/memcontrol.c:4494:9: sparse:    struct mem_cgroup_threshold_ary [noderef] __rcu *
   mm/memcontrol.c:4494:9: sparse:    struct mem_cgroup_threshold_ary *
   mm/memcontrol.c:6206:23: sparse: sparse: incompatible types in comparison expression (different address spaces):
   mm/memcontrol.c:6206:23: sparse:    struct task_struct [noderef] __rcu *
   mm/memcontrol.c:6206:23: sparse:    struct task_struct *
   mm/memcontrol.c:6443:52: sparse: sparse: incompatible types in comparison expression (different address spaces):
   mm/memcontrol.c:6443:52: sparse:    struct task_struct [noderef] __rcu *
   mm/memcontrol.c:6443:52: sparse:    struct task_struct *
   mm/memcontrol.c: note: in included file:
   include/linux/memcontrol.h:761:9: sparse: sparse: context imbalance in 'folio_lruvec_lock' - wrong count at exit
   include/linux/memcontrol.h:761:9: sparse: sparse: context imbalance in 'folio_lruvec_lock_irq' - wrong count at exit
   include/linux/memcontrol.h:761:9: sparse: sparse: context imbalance in 'folio_lruvec_lock_irqsave' - wrong count at exit
   mm/memcontrol.c:2095:6: sparse: sparse: context imbalance in 'folio_memcg_lock' - wrong count at exit
   mm/memcontrol.c:2142:17: sparse: sparse: context imbalance in '__folio_memcg_unlock' - unexpected unlock
   mm/memcontrol.c:6056:28: sparse: sparse: context imbalance in 'mem_cgroup_count_precharge_pte_range' - unexpected unlock
   mm/memcontrol.c:6251:36: sparse: sparse: context imbalance in 'mem_cgroup_move_charge_pte_range' - unexpected unlock

vim +3016 mm/memcontrol.c

  3003	
  3004	static struct obj_cgroup *current_objcg_update(struct obj_cgroup *old)
  3005	{
  3006		struct mem_cgroup *memcg;
  3007		struct obj_cgroup *objcg = NULL, *tmp = old;
  3008	
  3009		old = current_objcg_without_update_flag(old);
  3010		if (old)
  3011			obj_cgroup_put(old);
  3012	
  3013		rcu_read_lock();
  3014		do {
  3015			/* Atomically drop the update bit, */
> 3016			WARN_ON_ONCE(cmpxchg(&current->objcg, tmp, 0) != tmp);
  3017	
  3018			/* ...obtain the new objcg pointer */
  3019			memcg = mem_cgroup_from_task(current);
  3020			for (; memcg != root_mem_cgroup; memcg = parent_mem_cgroup(memcg)) {
  3021				objcg = rcu_dereference(memcg->objcg);
  3022				if (objcg && obj_cgroup_tryget(objcg))
  3023					break;
  3024				objcg = NULL;
  3025			}
  3026	
  3027			/*
  3028			 * ...and try atomically set up a new objcg pointer. If it
  3029			 * fails, it means the update flag was set concurrently, so
  3030			 * the whole procedure should be repeated.
  3031			 */
  3032			tmp = 0;
  3033		} while (!try_cmpxchg(&current->objcg, &tmp, objcg));
  3034		rcu_read_unlock();
  3035	
  3036		return objcg;
  3037	}
  3038	

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