The patch titled
Subject: mm: read page_type using READ_ONCE
has been added to the -mm mm-unstable branch. Its filename is
mm-read-page_type-using-read_once.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-read-page_type-using-read_once.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: David Hildenbrand <david@xxxxxxxxxx>
Subject: mm: read page_type using READ_ONCE
Date: Fri, 31 May 2024 14:56:16 +0200
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@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-lkp/202405281431.c46a3be9-lkp@xxxxxxxxx
Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
Reviewed-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/page-flags.h | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
--- a/include/linux/page-flags.h~mm-read-page_type-using-read_once
+++ a/include/linux/page-flags.h
@@ -949,9 +949,9 @@ 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)
{
@@ -960,7 +960,7 @@ static inline int page_type_has_type(uns
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) \
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
mm-memory-move-page_count-check-into-validate_page_before_insert.patch
mm-memory-cleanly-support-zeropage-in-vm_insert_page-vm_map_pages-and-vmf_insert_mixed.patch
mm-rmap-sanity-check-that-zeropages-are-not-passed-to-rmap.patch
fs-proc-task_mmu-indicate-pm_file-for-pmd-mapped-file-thp.patch
fs-proc-task_mmu-dont-indicate-pm_mmap_exclusive-without-pm_present.patch
fs-proc-task_mmu-properly-detect-pm_mmap_exclusive-per-page-of-pmd-mapped-thps.patch
fs-proc-task_mmu-account-non-present-entries-as-maybe-shared-but-no-idea-how-often.patch
fs-proc-move-page_mapcount-to-fs-proc-internalh.patch
documentation-admin-guide-mm-pagemaprst-drop-using-pagemap-to-do-something-useful.patch
mm-pass-meminit_context-to-__free_pages_core.patch
mm-pass-meminit_context-to-__free_pages_core-fix.patch
mm-pass-meminit_context-to-__free_pages_core-fix-2.patch
mm-pass-meminit_context-to-__free_pages_core-fix-3.patch
mm-memory_hotplug-initialize-memmap-of-zone_device-with-pageoffline-instead-of-pagereserved.patch
mm-memory_hotplug-skip-adjust_managed_page_count-for-pageoffline-pages-when-offlining.patch
mm-highmem-reimplement-totalhigh_pages-by-walking-zones.patch
mm-highmem-reimplement-totalhigh_pages-by-walking-zones-fix.patch
mm-highmem-make-nr_free_highpages-return-unsigned-long.patch
mm-read-page_type-using-read_once.patch
