The patch titled
Subject: mm: fix is_pinnable_page against on cma page
has been added to the -mm mm-unstable branch. Its filename is
mm-fix-is_pinnable_page-against-on-cma-page.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-fix-is_pinnable_page-against-on-cma-page.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: Minchan Kim <minchan@xxxxxxxxxx>
Subject: mm: fix is_pinnable_page against on cma page
Pages on CMA area could have MIGRATE_ISOLATE as well as MIGRATE_CMA so
current is_pinnable_page could miss CMA pages which has MIGRATE_ ISOLATE.
It ends up pinning CMA pages as longterm at pin_user_pages APIs so CMA
allocation keep failed until the pin is released.
CPU 0 CPU 1 - Task B
cma_alloc
alloc_contig_range
pin_user_pages_fast(FOLL_LONGTERM)
change pageblock as MIGRATE_ISOLATE
internal_get_user_pages_fast
lockless_pages_from_mm
gup_pte_range
try_grab_folio
is_pinnable_page
return true;
So, pinned the page successfully.
page migration failure with pinned page
..
.. After 30 sec
unpin_user_page(page)
CMA allocation succeeded after 30 sec.
The CMA allocation path protects the migration type change race using
zone->lock but what GUP path need to know is just whether the page is on
CMA area or not rather than exact migration type. Thus, we don't need
zone->lock but just checks migration type in either of (MIGRATE_ISOLATE
and MIGRATE_CMA).
Adding the MIGRATE_ISOLATE check in is_pinnable_page could cause rejecting
of pinning pages on MIGRATE_ISOLATE pageblocks even though it's neither
CMA nor movable zone if the page is temporarily unmovable. However, such
a migration failure by unexpected temporary refcount holding is a general
issue, not only coming from MIGRATE_ISOLATE and the MIGRATE_ISOLATE is
also a transient state like other temporarily elevated refcount problem.
Link: https://lkml.kernel.org/r/20220510211743.95831-1-minchan@xxxxxxxxxx
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: "Paul E . McKenney" <paulmck@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: John Dias <joaodias@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mm.h | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)
--- a/include/linux/mm.h~mm-fix-is_pinnable_page-against-on-cma-page
+++ a/include/linux/mm.h
@@ -1625,8 +1625,19 @@ static inline bool page_needs_cow_for_dm
#ifdef CONFIG_MIGRATION
static inline bool is_pinnable_page(struct page *page)
{
- return !(is_zone_movable_page(page) || is_migrate_cma_page(page)) ||
- is_zero_pfn(page_to_pfn(page));
+#ifdef CONFIG_CMA
+ /*
+ * use volatile to use local variable mt instead of
+ * refetching mt value.
+ */
+ int __mt = get_pageblock_migratetype(page);
+ int mt = __READ_ONCE(__mt);
+
+ if (mt == MIGRATE_CMA || mt == MIGRATE_ISOLATE)
+ return false;
+#endif
+
+ return !(is_zone_movable_page(page) || is_zero_pfn(page_to_pfn(page)));
}
#else
static inline bool is_pinnable_page(struct page *page)
_
Patches currently in -mm which might be from minchan@xxxxxxxxxx are
mm-fix-is_pinnable_page-against-on-cma-page.patch
