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 putting CMA pages longterm pinning possible on
pin_user_pages APIs so CMA allocation fails.
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 type. Thus, we don't
need zone->lock but just checks the migratype in either of
(MIGRATE_ISOLATE and MIGRATE_CMA).
Adding the MIGRATE_ISOLATE check in is_pinnable_page could cause
rejecting of pinning the page on MIGRATE_ISOLATE pageblock even
thouth it's neither CMA nor movable zone if the page is temporarily
unmovable. However, the migration failure is general issue, not
only come from MIGRATE_ISOLATE and the MIGRATE_ISOLATE is also
transient state like other temporal refcount holding of pages.
Cc: David Hildenbrand <[email protected]>
Signed-off-by: Minchan Kim <[email protected]>
---
* from v2 - https://lore.kernel.org/all/[email protected]/
* Use __READ_ONCE instead of volatile - akpm
* from v1 - https://lore.kernel.org/all/[email protected]/
* 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 | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 6acca5cecbc5..cbf79eb790e0 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1625,8 +1625,19 @@ 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
+ /*
+ * 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)
--
2.36.0.512.ge40c2bad7a-goog