The quilt patch titled
Subject: mm: read page_type using READ_ONCE
has been removed from the -mm tree. Its filename was
mm-read-page_type-using-read_once.patch
This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
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
@@ -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(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
