write_scan_unavictable_node checks the value req returned by
strict_strtoul and returns 1 if req is 0.

However, when strict_strtoul returns 0, it means successful conversion
of buf to unsigned long.

Due to this, the function was not proceeding to scan the zones for
unevictable pages even though we write a valid value to the 
scan_unevictable_pages sys file.

Changing this if check slightly to check for invalid value 
in buf as well as 0 value stored in res after successful conversion
via strict_strtoul.
In both cases, we do not perform the scanning of this node's zones.

Signed-off-by: Kautuk Consul <consul.kautuk@gmail.com>
---
 mm/vmscan.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index b55699c..73996e6 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3450,8 +3450,8 @@ static ssize_t write_scan_unevictable_node(struct sys_device *dev,
 	unsigned long res;
 	unsigned long req = strict_strtoul(buf, 10, &res);
 
-	if (!req)
-		return 1;	/* zero is no-op */
+	if (req || !res)
+		return 1; /* Invalid input or zero is no-op */
 
 	for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; ++zone) {
 		if (!populated_zone(zone))
-- 
1.7.4.1