Commit fde47708 authored by Zi Yan's avatar Zi Yan Committed by Andrew Morton
Browse files

mm/huge_memory: refactor after-split (page) cache code 

Smatch/coverity checkers report NULL mapping referencing issues[1][2][3]
every time the code is modified, because they do not understand that
mapping cannot be NULL when a folio is in page cache in the code. 
Refactor the code to make it explicit.

Remove "end = -1" for anonymous folios, since after code refactoring, end
is no longer used by anonymous folio handling code.

No functional change is intended.

Link: https://lkml.kernel.org/r/20250718023000.4044406-7-ziy@nvidia.com
Link: https://lore.kernel.org/linux-mm/2afe3d59-aca5-40f7-82a3-a6d976fb0f4f@stanley.mountain/ [1]
Link: https://lore.kernel.org/oe-kbuild/64b54034-f311-4e7d-b935-c16775dbb642@suswa.mountain/ [2]
Link: https://lore.kernel.org/linux-mm/20250716145804.4836-1-antonio@mandelbit.com/ [3]
Link: https://lkml.kernel.org/r/20250718183720.4054515-7-ziy@nvidia.com


Signed-off-by: default avatarZi Yan <ziy@nvidia.com>
Suggested-by: default avatarDavid Hildenbrand <david@redhat.com>
Acked-by: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarLorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Balbir Singh <balbirs@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Dan Carpenter <dan.carpenter@linaro.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Kirill A. Shutemov <k.shutemov@gmail.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Mathew Brost <matthew.brost@intel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent a3871560

mm/huge_memory.c

+28 −16
Original line number Diff line number Diff line
@@ -3640,7 +3640,6 @@ static int __folio_split(struct folio *folio, unsigned int new_order, 
			ret = -EBUSY;

			goto out;

		}

		end = -1;

		mapping = NULL;

		anon_vma_lock_write(anon_vma);

	} else {
@@ -3793,6 +3792,8 @@ static int __folio_split(struct folio *folio, unsigned int new_order, 
		 */

		for (new_folio = folio_next(folio); new_folio != end_folio;

		     new_folio = next) {

			unsigned long nr_pages = folio_nr_pages(new_folio);



			next = folio_next(new_folio);



			expected_refs = folio_expected_ref_count(new_folio) + 1;
@@ -3800,25 +3801,36 @@ static int __folio_split(struct folio *folio, unsigned int new_order, 


			lru_add_split_folio(folio, new_folio, lruvec, list);



			/* Some pages can be beyond EOF: drop them from cache */

			if (new_folio->index >= end) {

				if (shmem_mapping(mapping))

					nr_shmem_dropped += folio_nr_pages(new_folio);

				else if (folio_test_clear_dirty(new_folio))

					folio_account_cleaned(

						new_folio,

						inode_to_wb(mapping->host));

				__filemap_remove_folio(new_folio, NULL);

				folio_put_refs(new_folio,

					       folio_nr_pages(new_folio));

			} else if (mapping) {

				__xa_store(&mapping->i_pages, new_folio->index,

					   new_folio, 0);

			} else if (swap_cache) {

			/*

			 * Anonymous folio with swap cache.

			 * NOTE: shmem in swap cache is not supported yet.

			 */

			if (swap_cache) {

				__xa_store(&swap_cache->i_pages,

					   swap_cache_index(new_folio->swap),

					   new_folio, 0);

				continue;

			}



			/* Anonymous folio without swap cache */

			if (!mapping)

				continue;



			/* Add the new folio to the page cache. */

			if (new_folio->index < end) {

				__xa_store(&mapping->i_pages, new_folio->index,

					   new_folio, 0);

				continue;

			}



			/* Drop folio beyond EOF: ->index >= end */

			if (shmem_mapping(mapping))

				nr_shmem_dropped += nr_pages;

			else if (folio_test_clear_dirty(new_folio))

				folio_account_cleaned(

					new_folio, inode_to_wb(mapping->host));

			__filemap_remove_folio(new_folio, NULL);

			folio_put_refs(new_folio, nr_pages);

		}

		/*

		 * Unfreeze @folio only after all page cache entries, which