kernel/bpf/helpers.c:1960:13: sparse: sparse: Using plain integer as NULL pointer

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

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   037266a5f7239ead1530266f7d7af153d2a867fa
commit: c3c510ce431cd99fa10dcd50d995c8e89330ee5b bpf: Add 'owner' field to bpf_{list,rb}_node
date:   4 months ago
config: hexagon-randconfig-r121-20231119 (https://download.01.org/0day-ci/archive/20231120/202311200222.YfH38g2S-lkp@intel.com/config)
compiler: clang version 17.0.0 (https://github.com/llvm/llvm-project.git 4a5ac14ee968ff0ad5d2cc1ffa0299048db4c88a)
reproduce: (https://download.01.org/0day-ci/archive/20231120/202311200222.YfH38g2S-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/202311200222.YfH38g2S-lkp@intel.com/

sparse warnings: (new ones prefixed by >>)
>> kernel/bpf/helpers.c:1960:13: sparse: sparse: Using plain integer as NULL pointer
   kernel/bpf/helpers.c:2059:13: sparse: sparse: Using plain integer as NULL pointer
   kernel/bpf/helpers.c: note: in included file (through include/linux/mmzone.h, include/linux/gfp.h, include/linux/umh.h, include/linux/kmod.h, ...):
   include/linux/page-flags.h:240:46: sparse: sparse: self-comparison always evaluates to false
   kernel/bpf/helpers.c:2419:18: sparse: sparse: context imbalance in 'bpf_rcu_read_lock' - wrong count at exit
   kernel/bpf/helpers.c:2424:18: sparse: sparse: context imbalance in 'bpf_rcu_read_unlock' - unexpected unlock

vim +1960 kernel/bpf/helpers.c

  1944	
  1945	static int __bpf_list_add(struct bpf_list_node_kern *node,
  1946				  struct bpf_list_head *head,
  1947				  bool tail, struct btf_record *rec, u64 off)
  1948	{
  1949		struct list_head *n = &node->list_head, *h = (void *)head;
  1950	
  1951		/* If list_head was 0-initialized by map, bpf_obj_init_field wasn't
  1952		 * called on its fields, so init here
  1953		 */
  1954		if (unlikely(!h->next))
  1955			INIT_LIST_HEAD(h);
  1956	
  1957		/* node->owner != NULL implies !list_empty(n), no need to separately
  1958		 * check the latter
  1959		 */
> 1960		if (cmpxchg(&node->owner, NULL, BPF_PTR_POISON)) {
  1961			/* Only called from BPF prog, no need to migrate_disable */
  1962			__bpf_obj_drop_impl((void *)n - off, rec);
  1963			return -EINVAL;
  1964		}
  1965	
  1966		tail ? list_add_tail(n, h) : list_add(n, h);
  1967		WRITE_ONCE(node->owner, head);
  1968	
  1969		return 0;
  1970	}
  1971	

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