[PATCH 3/4] mm/hugeltb: fix potential wrong gbl_reserve value for hugetlb_acct_memory()

[Miaohe Lin <linmiaohe@huawei.com>]

The resv_map could be NULL since this routine can be called in the evict
inode path for all hugetlbfs inodes. So we could have chg = 0 and this
would result in a negative value when chg - freed. This is unexpected for
hugepage_subpool_put_pages() and hugetlb_acct_memory().

Fixes: b5cec28d36f5 ("hugetlbfs: truncate_hugepages() takes a range of pages")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
 mm/hugetlb.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index b7864abded3d..bdff8d23803f 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5413,6 +5413,7 @@ long hugetlb_unreserve_pages(struct inode *inode, long start, long end,
 	long chg = 0;
 	struct hugepage_subpool *spool = subpool_inode(inode);
 	long gbl_reserve;
+	long delta;
 
 	/*
 	 * Since this routine can be called in the evict inode path for all
@@ -5437,7 +5438,8 @@ long hugetlb_unreserve_pages(struct inode *inode, long start, long end,
 	 * If the subpool has a minimum size, the number of global
 	 * reservations to be released may be adjusted.
 	 */
-	gbl_reserve = hugepage_subpool_put_pages(spool, (chg - freed));
+	delta = chg > 0 ? chg - freed : freed;
+	gbl_reserve = hugepage_subpool_put_pages(spool, delta);
 	hugetlb_acct_memory(h, -gbl_reserve);
 
 	return 0;
-- 
2.19.1