linux-kernel - [PATCH v3] mm: fix is_pinnable

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Date:   Mon,  9 May 2022 08:34:30 -0700
From:   Minchan Kim <minchan@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        John Hubbard <jhubbard@...dia.com>,
        John Dias <joaodias@...gle.com>,
        Minchan Kim <minchan@...nel.org>,
        David Hildenbrand <david@...hat.com>
Subject: [PATCH v3] 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 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 <david@...hat.com>
Signed-off-by: Minchan Kim <minchan@...nel.org>
---
* from v2 - https://lore.kernel.org/all/20220505064429.2818496-1-minchan@kernel.org/
  * Use __READ_ONCE instead of volatile - akpm

* from v1 - https://lore.kernel.org/all/20220502173558.2510641-1-minchan@kernel.org/
  * 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