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 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.
Cc: "Paul E . McKenney" <paulmck@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
* from v5 - https://lore.kernel.org/all/20220512204143.3961150-1-minchan@xxxxxxxxxx/
* Use READ_ONCE in __get_pfnblock_flags_mask - Jason
* adding a comment about READ_ONCE - John
* from v4 - https://lore.kernel.org/all/20220510211743.95831-1-minchan@xxxxxxxxxx/
* clarification why we need READ_ONCE - Paul
* Adding a comment about READ_ONCE - John
* from v3 - https://lore.kernel.org/all/20220509153430.4125710-1-minchan@xxxxxxxxxx/
* Fix typo and adding more description - akpm
* from v2 - https://lore.kernel.org/all/20220505064429.2818496-1-minchan@xxxxxxxxxx/
* Use __READ_ONCE instead of volatile - akpm
* from v1 - https://lore.kernel.org/all/20220502173558.2510641-1-minchan@xxxxxxxxxx/
* fix build warning - lkp
* fix refetching issue of migration type
* add side effect on !ZONE_MOVABLE and !MIGRATE_CMA in description - david
include/linux/mm.h | 9 +++++++--
mm/page_alloc.c | 8 ++++++--
2 files changed, 13 insertions(+), 4 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 6acca5cecbc5..ba13411b6dca 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1625,8 +1625,13 @@ static inline bool page_needs_cow_for_dma(struct vm_area_struct *vma,
#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)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7a2053621e27..348071e5d8d9 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -482,8 +482,12 @@ unsigned long __get_pfnblock_flags_mask(const struct page *page,
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;
}
--
2.36.1.124.g0e6072fb45-goog
