The patch titled
Subject: mm: fix is_pinnable_page against a cma page
has been added to the -mm mm-unstable branch. Its filename is
mm-fix-is_pinnable_page-against-a-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-a-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 a cma page
Date: Tue, 24 May 2022 10:15:25 -0700
Pages in the CMA area could have MIGRATE_ISOLATE as well as MIGRATE_CMA so
the current is_pinnable_page() could miss CMA pages which have
MIGRATE_ISOLATE. It ends up pinning CMA pages as longterm for the
pin_user_pages() API so CMA allocations keep failing 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 temporal refcount holding is general
issue, not only come from MIGRATE_ISOLATE and the MIGRATE_ISOLATE is also
transient state like other temporal elevated refcount problem.
Link: https://lkml.kernel.org/r/20220524171525.976723-1-minchan@xxxxxxxxxx
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>
Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mm.h | 9 +++++++--
mm/page_alloc.c | 8 ++++++--
2 files changed, 13 insertions(+), 4 deletions(-)
--- a/include/linux/mm.h~mm-fix-is_pinnable_page-against-a-cma-page
+++ a/include/linux/mm.h
@@ -1594,8 +1594,13 @@ 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
+ int mt = get_pageblock_migratetype(page);
+
+ 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)
--- a/mm/page_alloc.c~mm-fix-is_pinnable_page-against-a-cma-page
+++ a/mm/page_alloc.c
@@ -490,8 +490,12 @@ unsigned long __get_pfnblock_flags_mask(
bitidx = pfn_to_bitidx(page, pfn);
word_bitidx = bitidx / BITS_PER_LONG;
bitidx &= (BITS_PER_LONG-1);
-
- word = bitmap[word_bitidx];
+ /*
+ * This races, without locks, with set_pfnblock_flags_mask(). Ensure
+ * a consistent read of the memory array, so that results, even though
+ * racy, are not corrupted.
+ */
+ word = READ_ONCE(bitmap[word_bitidx]);
return (word >> bitidx) & mask;
}
_
Patches currently in -mm which might be from minchan@xxxxxxxxxx are
mm-fix-is_pinnable_page-against-a-cma-page.patch
