[patch] mm, compaction: properly initialize alloc_flags in compact_control

[David Rientjes]

compaction_suitable() requires a useful cc->alloc_flags, otherwise the
results of compact_zone() can be indeterminate.  Kcompactd currently
checks compaction_suitable() itself with alloc_flags == 0, but passes an
uninitialized value from the stack to compact_zone(), which does its own
check.

The same is true for compact_node() when explicitly triggering full node
compaction.

Properly initialize cc.alloc_flags on the stack.

Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
---
 mm/compaction.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1792,9 +1792,9 @@ static void compact_node(int nid)
 {
 	pg_data_t *pgdat = NODE_DATA(nid);
 	int zoneid;
-	struct zone *zone;
 	struct compact_control cc = {
 		.order = -1,
+		.alloc_flags = 0,
 		.total_migrate_scanned = 0,
 		.total_free_scanned = 0,
 		.mode = MIGRATE_SYNC,
@@ -1805,6 +1805,7 @@ static void compact_node(int nid)
 
 
 	for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
+		struct zone *zone;
 
 		zone = &pgdat->node_zones[zoneid];
 		if (!populated_zone(zone))
@@ -1923,6 +1924,7 @@ static void kcompactd_do_work(pg_data_t *pgdat)
 	struct zone *zone;
 	struct compact_control cc = {
 		.order = pgdat->kcompactd_max_order,
+		.alloc_flags = 0,
 		.total_migrate_scanned = 0,
 		.total_free_scanned = 0,
 		.classzone_idx = pgdat->kcompactd_classzone_idx,
@@ -1945,8 +1947,8 @@ static void kcompactd_do_work(pg_data_t *pgdat)
 		if (compaction_deferred(zone, cc.order))
 			continue;
 
-		if (compaction_suitable(zone, cc.order, 0, zoneid) !=
-							COMPACT_CONTINUE)
+		if (compaction_suitable(zone, cc.order, cc.alloc_flags,
+					zoneid) != COMPACT_CONTINUE)
 			continue;
 
 		cc.nr_freepages = 0;