[linux-next:master 10324/10719] mm/huge_memory.c:3587:46: sparse: sparse: Using plain integer as NULL pointer

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

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
head:   9fbcd7b32bf7c0a5bda0f22c25df29d00a872017
commit: fb4b4b748b3a140c49115c9ad2973d56e6e1f7c5 [10324/10719] mm/huge_memory: unfreeze head folio after page cache entries are updated
config: mips-randconfig-r132-20250313 (https://download.01.org/0day-ci/archive/20250313/202503131109.s7iuWfGq-lkp@intel.com/config)
compiler: mips-linux-gcc (GCC) 14.2.0
reproduce: (https://download.01.org/0day-ci/archive/20250313/202503131109.s7iuWfGq-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/202503131109.s7iuWfGq-lkp@intel.com/

sparse warnings: (new ones prefixed by >>)
>> mm/huge_memory.c:3587:46: sparse: sparse: Using plain integer as NULL pointer
   mm/huge_memory.c: note: in included file (through include/linux/mmzone.h, include/linux/gfp.h, include/linux/mm.h):
   include/linux/page-flags.h:275:46: sparse: sparse: self-comparison always evaluates to false
   include/linux/page-flags.h:275:46: sparse: sparse: self-comparison always evaluates to false
   mm/huge_memory.c:2191:20: sparse: sparse: context imbalance in 'madvise_free_huge_pmd' - unexpected unlock
   include/linux/page-flags.h:275:46: sparse: sparse: self-comparison always evaluates to false
   mm/huge_memory.c:2229:28: sparse: sparse: context imbalance in 'zap_huge_pmd' - unexpected unlock
   mm/huge_memory.c:2353:28: sparse: sparse: context imbalance in 'move_huge_pmd' - unexpected unlock
   mm/huge_memory.c:2493:20: sparse: sparse: context imbalance in 'change_huge_pmd' - unexpected unlock
   mm/huge_memory.c:2690:12: sparse: sparse: context imbalance in '__pmd_trans_huge_lock' - wrong count at exit
   include/linux/page-flags.h:275:46: sparse: sparse: self-comparison always evaluates to false
   mm/huge_memory.c:3450:27: sparse: sparse: context imbalance in '__split_huge_page' - unexpected unlock
   include/linux/page-flags.h:275:46: sparse: sparse: self-comparison always evaluates to false
   mm/huge_memory.c: note: in included file (through include/linux/mm.h):
   include/linux/page_ref.h:291:27: sparse: sparse: context imbalance in '__split_unmapped_folio' - unexpected unlock
   mm/huge_memory.c:4112:17: sparse: sparse: context imbalance in 'split_huge_page_to_list_to_order' - different lock contexts for basic block
   mm/huge_memory.c: note: in included file (through include/linux/mmzone.h, include/linux/gfp.h, include/linux/mm.h):
   include/linux/page-flags.h:275:46: sparse: sparse: self-comparison always evaluates to false
   mm/huge_memory.c:4546:17: sparse: sparse: context imbalance in 'split_huge_pages_pid' - unexpected unlock

vim +3587 mm/huge_memory.c

  3518	
  3519	/*
  3520	 * It splits @folio into @new_order folios and copies the @folio metadata to
  3521	 * all the resulting folios.
  3522	 */
  3523	static void __split_folio_to_order(struct folio *folio, int old_order,
  3524			int new_order)
  3525	{
  3526		long new_nr_pages = 1 << new_order;
  3527		long nr_pages = 1 << old_order;
  3528		long i;
  3529	
  3530		/*
  3531		 * Skip the first new_nr_pages, since the new folio from them have all
  3532		 * the flags from the original folio.
  3533		 */
  3534		for (i = new_nr_pages; i < nr_pages; i += new_nr_pages) {
  3535			struct page *new_head = &folio->page + i;
  3536	
  3537			/*
  3538			 * Careful: new_folio is not a "real" folio before we cleared PageTail.
  3539			 * Don't pass it around before clear_compound_head().
  3540			 */
  3541			struct folio *new_folio = (struct folio *)new_head;
  3542	
  3543			VM_BUG_ON_PAGE(atomic_read(&new_folio->_mapcount) != -1, new_head);
  3544	
  3545			/*
  3546			 * Clone page flags before unfreezing refcount.
  3547			 *
  3548			 * After successful get_page_unless_zero() might follow flags change,
  3549			 * for example lock_page() which set PG_waiters.
  3550			 *
  3551			 * Note that for mapped sub-pages of an anonymous THP,
  3552			 * PG_anon_exclusive has been cleared in unmap_folio() and is stored in
  3553			 * the migration entry instead from where remap_page() will restore it.
  3554			 * We can still have PG_anon_exclusive set on effectively unmapped and
  3555			 * unreferenced sub-pages of an anonymous THP: we can simply drop
  3556			 * PG_anon_exclusive (-> PG_mappedtodisk) for these here.
  3557			 */
  3558			new_folio->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
  3559			new_folio->flags |= (folio->flags &
  3560					((1L << PG_referenced) |
  3561					 (1L << PG_swapbacked) |
  3562					 (1L << PG_swapcache) |
  3563					 (1L << PG_mlocked) |
  3564					 (1L << PG_uptodate) |
  3565					 (1L << PG_active) |
  3566					 (1L << PG_workingset) |
  3567					 (1L << PG_locked) |
  3568					 (1L << PG_unevictable) |
  3569	#ifdef CONFIG_ARCH_USES_PG_ARCH_2
  3570					 (1L << PG_arch_2) |
  3571	#endif
  3572	#ifdef CONFIG_ARCH_USES_PG_ARCH_3
  3573					 (1L << PG_arch_3) |
  3574	#endif
  3575					 (1L << PG_dirty) |
  3576					 LRU_GEN_MASK | LRU_REFS_MASK));
  3577	
  3578			new_folio->mapping = folio->mapping;
  3579			new_folio->index = folio->index + i;
  3580	
  3581			/*
  3582			 * page->private should not be set in tail pages. Fix up and warn once
  3583			 * if private is unexpectedly set.
  3584			 */
  3585			if (unlikely(new_folio->private)) {
  3586				VM_WARN_ON_ONCE_PAGE(true, new_head);
> 3587				new_folio->private = 0;
  3588			}
  3589	
  3590			if (folio_test_swapcache(folio))
  3591				new_folio->swap.val = folio->swap.val + i;
  3592	
  3593			/* Page flags must be visible before we make the page non-compound. */
  3594			smp_wmb();
  3595	
  3596			/*
  3597			 * Clear PageTail before unfreezing page refcount.
  3598			 *
  3599			 * After successful get_page_unless_zero() might follow put_page()
  3600			 * which needs correct compound_head().
  3601			 */
  3602			clear_compound_head(new_head);
  3603			if (new_order) {
  3604				prep_compound_page(new_head, new_order);
  3605				folio_set_large_rmappable(new_folio);
  3606			}
  3607	
  3608			if (folio_test_young(folio))
  3609				folio_set_young(new_folio);
  3610			if (folio_test_idle(folio))
  3611				folio_set_idle(new_folio);
  3612	
  3613			folio_xchg_last_cpupid(new_folio, folio_last_cpupid(folio));
  3614		}
  3615	
  3616		if (new_order)
  3617			folio_set_order(folio, new_order);
  3618		else
  3619			ClearPageCompound(&folio->page);
  3620	}
  3621	

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