+ mm-fix-is_pinnable_page-against-on-cma-page-v5.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm-fix-is_pinnable_page-against-on-cma-page-v5
has been added to the -mm mm-unstable branch.  Its filename is
     mm-fix-is_pinnable_page-against-on-cma-page-v5.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-v5.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@kernel.org>
Subject: mm-fix-is_pinnable_page-against-on-cma-page-v5

  * clarification why we need READ_ONCE - Paul
  * Add a comment about READ_ONCE - John

Link: https://lkml.kernel.org/r/20220512204143.3961150-1-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: "Paul E . McKenney" <paulmck@kernel.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/mm.h |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

--- a/include/linux/mm.h~mm-fix-is_pinnable_page-against-on-cma-page-v5
+++ a/include/linux/mm.h
@@ -1627,13 +1627,14 @@ static inline bool is_pinnable_page(stru
 {
 #ifdef CONFIG_CMA
 	/*
-	 * use volatile to use local variable mt instead of
-	 * refetching mt value.
+	 * Defend against future compiler LTO features, or code refactoring
+	 * that inlines the above function, by forcing a single read. Because,
+	 * this routine races with set_pageblock_migratetype(), and we want to
+	 * avoid reading zero, when actually one or the other flags was set.
 	 */
-	int __mt = get_pageblock_migratetype(page);
 	int mt = __READ_ONCE(__mt);
 
-	if (mt == MIGRATE_CMA || mt == MIGRATE_ISOLATE)
+	if (mt & (MIGRATE_CMA | MIGRATE_ISOLATE))
 		return false;
 #endif
 
_

Patches currently in -mm which might be from minchan@kernel.org are

mm-fix-is_pinnable_page-against-on-cma-page.patch
mm-fix-is_pinnable_page-against-on-cma-page-v5.patch
mm-dont-be-stuck-to-rmap-lock-on-reclaim-path.patch