mm: Fix return val in khugepaged_scan_pmd()

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4SK3S
CVE: NA

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The khugepaged_scan_pmd() should return 0 not SCAN_ALLOC_HUGE_PAGE_FAIL,
or mmap_sem will not be released in khugepaged_scan_mm_slot().

Fixes: 1845e7ad ("mm: Add reliable memory use limit for user tasks")
Signed-off-by: NMa Wupeng <mawupeng1@huawei.com>
Reviewed-by: NKefeng Wang <wangkefeng.wang@huawei.com>
Reviewed-by: NXie XiuQi <xiexiuqi@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

mm/khugepaged.c

@@ -1240,7 +1240,8 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
 				if (reliable_allow_fb_enabled()) {
 					reliable = false;
 				} else {
-					ret = SCAN_ALLOC_HUGE_PAGE_FAIL;
+					result = SCAN_ALLOC_HUGE_PAGE_FAIL;
+					ret = 0;
 					goto out;
 				}
 			}