[PATCH] mm: migrate: fix an incorrect call of prep_transhuge_page()

[Zi Yan <zi.yan@sent.com>]

From: Zi Yan <zi.yan@cs.rutgers.edu>

In [1], Andrea reported that during memory hotplug/hot remove
prep_transhuge_page() is called incorrectly on non-THP pages for
migration, when THP is on but THP migration is not enabled.
This leads to a bad state of target pages for migration.

This patch fixes it by only calling prep_transhuge_page() when we are
certain that the target page is THP.

[1] https://lkml.org/lkml/2017/11/20/411

Cc: stable@vger.kernel.org # v4.14
Fixes: 8135d8926c08 ("mm: memory_hotplug: memory hotremove supports thp migration")
Reported-by: Andrea Reale <ar@linux.vnet.ibm.com>
Signed-off-by: Zi Yan <zi.yan@cs.rutgers.edu>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: "JA(C)rA'me Glisse" <jglisse@redhat.com>
---
 include/linux/migrate.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 895ec0c4942e..a2246cf670ba 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -54,7 +54,7 @@ static inline struct page *new_page_nodemask(struct page *page,
 	new_page = __alloc_pages_nodemask(gfp_mask, order,
 				preferred_nid, nodemask);
 
-	if (new_page && PageTransHuge(page))
+	if (new_page && PageTransHuge(new_page))
 		prep_transhuge_page(new_page);
 
 	return new_page;
-- 
2.14.2

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