[davidhildenbrand:mm_id_6.14 5/13] mm/page_alloc.c:976:20: warning: this statement may fall through

[davidhildenbrand:mm_id_6.14 5/13] mm/page_alloc.c:976:20: warning: this statement may fall through

[kernel test robot]

tree:   https://github.com/davidhildenbrand/linux mm_id_6.14
head:   dcbc194183fd7526f260cc629aabff9d3300083e
commit: c599962b8dd50874ba583ccb6eb6cd9d2e973d45 [5/13] mm: move hugetlb specific things in folio to page[3]
config: riscv-randconfig-002-20250216 (https://download.01.org/0day-ci/archive/20250216/202502162207.5aJRjcne-lkp@intel.com/config)
compiler: riscv64-linux-gcc (GCC) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250216/202502162207.5aJRjcne-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/202502162207.5aJRjcne-lkp@intel.com/

All warnings (new ones prefixed by >>):

   mm/page_alloc.c: In function 'free_tail_page_prepare':
>> mm/page_alloc.c:976:20: warning: this statement may fall through [-Wimplicit-fallthrough=]
     976 |                 if (IS_ENABLED(CONFIG_HUGETLB_PAGE))
         |                    ^
   mm/page_alloc.c:978:9: note: here
     978 |         default:
         |         ^~~~~~~


vim +976 mm/page_alloc.c

   931	
   932	static int free_tail_page_prepare(struct page *head_page, struct page *page)
   933	{
   934		struct folio *folio = (struct folio *)head_page;
   935		int ret = 1;
   936	
   937		/*
   938		 * We rely page->lru.next never has bit 0 set, unless the page
   939		 * is PageTail(). Let's make sure that's true even for poisoned ->lru.
   940		 */
   941		BUILD_BUG_ON((unsigned long)LIST_POISON1 & 1);
   942	
   943		if (!is_check_pages_enabled()) {
   944			ret = 0;
   945			goto out;
   946		}
   947		switch (page - head_page) {
   948		case 1:
   949			/* the first tail page: these may be in place of ->mapping */
   950			if (unlikely(folio_entire_mapcount(folio))) {
   951				bad_page(page, "nonzero entire_mapcount");
   952				goto out;
   953			}
   954			if (unlikely(folio_large_mapcount(folio))) {
   955				bad_page(page, "nonzero large_mapcount");
   956				goto out;
   957			}
   958			if (unlikely(atomic_read(&folio->_nr_pages_mapped))) {
   959				bad_page(page, "nonzero nr_pages_mapped");
   960				goto out;
   961			}
   962			if (unlikely(atomic_read(&folio->_pincount))) {
   963				bad_page(page, "nonzero pincount");
   964				goto out;
   965			}
   966			break;
   967		case 2:
   968			/* the second tail page: deferred_list overlaps ->mapping */
   969			if (unlikely(!list_empty(&folio->_deferred_list))) {
   970				bad_page(page, "on deferred list");
   971				goto out;
   972			}
   973			break;
   974		case 3:
   975			/* the third tail page: hugetlb specifics overlaps ->mappings */
 > 976			if (IS_ENABLED(CONFIG_HUGETLB_PAGE))
   977				break;
   978		default:
   979			if (page->mapping != TAIL_MAPPING) {
   980				bad_page(page, "corrupted mapping in tail page");
   981				goto out;
   982			}
   983			break;
   984		}
   985		if (unlikely(!PageTail(page))) {
   986			bad_page(page, "PageTail not set");
   987			goto out;
   988		}
   989		if (unlikely(compound_head(page) != head_page)) {
   990			bad_page(page, "compound_head not consistent");
   991			goto out;
   992		}
   993		ret = 0;
   994	out:
   995		page->mapping = NULL;
   996		clear_compound_head(page);
   997		return ret;
   998	}
   999	

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