From: Baolin Wang <baolin.wang@linux.alibaba.com>
Date: Thu, 28 Apr 2022 23:16:09 -0700
Subject: mm: migrate: simplify the refcount validation when migrating hugetlb
 mapping
Git-commit: 9c42fe4e30a9b934b1de66c2edca196563221392
Patch-mainline: v5.19-rc1
References: jsc#PED-1247

There is no need to validate the hugetlb page's refcount before trying to
freeze the hugetlb page's expected refcount, instead we can just rely on
the page_ref_freeze() to simplify the validation.

Moreover we are always under the page lock when migrating the hugetlb page
mapping, which means nowhere else can remove it from the page cache, so we
can remove the xas_load() validation under the i_pages lock.

Link: https://lkml.kernel.org/r/eb2fbbeaef2b1714097b9dec457426d682ee0635.1649676424.git.baolin.wang@linux.alibaba.com
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
 mm/migrate.c |    5 -----
 1 file changed, 5 deletions(-)

--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -490,11 +490,6 @@ int migrate_huge_page_move_mapping(struc
 
 	xas_lock_irq(&xas);
 	expected_count = 2 + page_has_private(page);
-	if (page_count(page) != expected_count || xas_load(&xas) != page) {
-		xas_unlock_irq(&xas);
-		return -EAGAIN;
-	}
-
 	if (!page_ref_freeze(page, expected_count)) {
 		xas_unlock_irq(&xas);
 		return -EAGAIN;