mm/hugeltb: simplify the return code of __vma_reservation_common()

It's guaranteed that the vma is associated with a resv_map, i.e.  either
VM_MAYSHARE or HPAGE_RESV_OWNER, when the code reaches here or we would
have returned via !resv check above.  So it's unneeded to check whether
HPAGE_RESV_OWNER is set here.  Simplify the return code to make it more
clear.

Link: https://lkml.kernel.org/r/20210410072348.20437-3-linmiaohe@huawei.comSigned-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Feilong Lin <linfeilong@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/hugetlb.c

@@ -2174,8 +2174,9 @@ static long __vma_reservation_common(struct hstate *h,
 
 	if (vma->vm_flags & VM_MAYSHARE)
 		return ret;
-	else if (is_vma_resv_set(vma, HPAGE_RESV_OWNER) && ret >= 0) {
 	/*
+	 * We know private mapping must have HPAGE_RESV_OWNER set.
+	 *
 	 * In most cases, reserves always exist for private mappings.
 	 * However, a file associated with mapping could have been
 	 * hole punched or truncated after reserves were consumed.
@@ -2188,13 +2189,11 @@ static long __vma_reservation_common(struct hstate *h,
 	 * return value of this routine is the opposite of the
 	 * value returned from reserve map manipulation routines above.
 	 */
-		if (ret)
+	if (ret > 0)
 		return 0;
-		else
+	if (ret == 0)
 		return 1;
-	}
-	else
-		return ret < 0 ? ret : 0;
+	return ret;
 }
 
 static long vma_needs_reservation(struct hstate *h,