From dc9e6f7053dd540db2c9fba30c31a07de5edab01 Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Fri, 31 May 2024 14:56:16 +0200 Subject: [PATCH] mm: read page_type using READ_ONCE KCSAN complains about possible data races: while we check for a page_type -- for example for sanity checks -- we might concurrently modify the mapcount that overlays page_type. Let's use READ_ONCE to avoid load tearing (shouldn't make a difference) and to make KCSAN happy. Likely, we might also want to use WRITE_ONCE for the writer side of page_type, if KCSAN ever complains about that. But we'll not mess with that for now. Note: nothing should really be broken besides wrong KCSAN complaints. The sanity check that triggers this was added in commit 68f0320824fa ("mm/rmap: convert folio_add_file_rmap_range() into folio_add_file_rmap_[pte|ptes|pmd]()"). Even before that similar races likely where possible, ever since we added page_type in commit 6e292b9be7f4 ("mm: split page_type out from _mapcount"). Link: https://lkml.kernel.org/r/20240531125616.2850153-1-david@redhat.com Signed-off-by: David Hildenbrand Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-lkp/202405281431.c46a3be9-lkp@intel.com Reviewed-by: Oscar Salvador Reviewed-by: Miaohe Lin Cc: Matthew Wilcox Signed-off-by: Andrew Morton --- include/linux/page-flags.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index 1d441908b726..5769fe6e4950 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -955,9 +955,9 @@ enum pagetype { }; #define PageType(page, flag) \ - ((page->page_type & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE) + ((READ_ONCE(page->page_type) & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE) #define folio_test_type(folio, flag) \ - ((folio->page.page_type & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE) + ((READ_ONCE(folio->page.page_type) & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE) static inline int page_type_has_type(unsigned int page_type) { @@ -966,7 +966,7 @@ static inline int page_type_has_type(unsigned int page_type) static inline int page_has_type(const struct page *page) { - return page_type_has_type(page->page_type); + return page_type_has_type(READ_ONCE(page->page_type)); } #define FOLIO_TYPE_OPS(lname, fname) \ -- 2.49.0