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Date:   Thu, 21 May 2020 06:49:51 -0700 (PDT)
From:   Hugh Dickins <hughd@google.com>
To:     Andrew Morton <akpm@linux-foundation.org>
cc:     Anshuman Khandual <anshuman.khandual@arm.com>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        Zi Yan <ziy@nvidia.com>, John Hubbard <jhubbard@nvidia.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: [PATCH mmotm] mm/vmstat: Add events for PMD based THP migration
 without split fix
Message-ID: <alpine.LSU.2.11.2005210643340.482@eggly.anvils>
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Fix 5.7-rc6-mm1 page migration crash in unmap_and_move(): when the
page to be migrated has been freed from under us, that is considered 
a MIGRATEPAGE_SUCCESS, but no newpage has been allocated (and I don't
think it would ever need to be counted as a successful THP migration).

Signed-off-by: Hugh Dickins <hughd@google.com>
---
Fix to mm-vmstat-add-events-for-pmd-based-thp-migration-without-split.patch

 mm/migrate.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- 5.7-rc6-mm1/mm/migrate.c	2020-05-20 12:21:56.117693827 -0700
+++ linux/mm/migrate.c	2020-05-20 15:08:12.319476978 -0700
@@ -1248,7 +1248,7 @@ out:
 	 * we want to retry.
 	 */
 	if (rc == MIGRATEPAGE_SUCCESS) {
-		if (PageTransHuge(newpage))
+		if (newpage && PageTransHuge(newpage))
 			thp_migration_success(true);
 		put_page(page);
 		if (reason == MR_MEMORY_FAILURE) {