[PATCH v4 7/8] memcg: warn for unexpected events and stats

[Shakeel Butt <shakeel.butt@xxxxxxxxx>]

To reduce memory usage by the memcg events and stats, the kernel uses
indirection table and only allocate stats and events which are being
used by the memcg code. To make this more robust, let's add warnings
where unexpected stats and events indexes are used.

Signed-off-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
---
Changes since v3:
- N/A

 mm/memcontrol.c | 39 +++++++++++++++++++++++----------------
 1 file changed, 23 insertions(+), 16 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a78cf00dd537..b4a1b4bb599d 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -671,7 +671,7 @@ unsigned long lruvec_page_state(struct lruvec *lruvec, enum node_stat_item idx)
 		return node_page_state(lruvec_pgdat(lruvec), idx);
 
 	i = memcg_stats_index(idx);
-	if (i < 0)
+	if (WARN_ONCE(i < 0, "%s: missing stat item %d\n", __func__, idx))
 		return 0;
 
 	pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
@@ -687,14 +687,14 @@ unsigned long lruvec_page_state_local(struct lruvec *lruvec,
 				      enum node_stat_item idx)
 {
 	struct mem_cgroup_per_node *pn;
-	long x = 0;
+	long x;
 	int i;
 
 	if (mem_cgroup_disabled())
 		return node_page_state(lruvec_pgdat(lruvec), idx);
 
 	i = memcg_stats_index(idx);
-	if (i < 0)
+	if (WARN_ONCE(i < 0, "%s: missing stat item %d\n", __func__, idx))
 		return 0;
 
 	pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
@@ -923,7 +923,7 @@ unsigned long memcg_page_state(struct mem_cgroup *memcg, int idx)
 	long x;
 	int i = memcg_stats_index(idx);
 
-	if (i < 0)
+	if (WARN_ONCE(i < 0, "%s: missing stat item %d\n", __func__, idx))
 		return 0;
 
 	x = READ_ONCE(memcg->vmstats->state[i]);
@@ -960,7 +960,10 @@ void __mod_memcg_state(struct mem_cgroup *memcg, int idx, int val)
 {
 	int i = memcg_stats_index(idx);
 
-	if (mem_cgroup_disabled() || i < 0)
+	if (mem_cgroup_disabled())
+		return;
+
+	if (WARN_ONCE(i < 0, "%s: missing stat item %d\n", __func__, idx))
 		return;
 
 	__this_cpu_add(memcg->vmstats_percpu->state[i], val);
@@ -973,7 +976,7 @@ static unsigned long memcg_page_state_local(struct mem_cgroup *memcg, int idx)
 	long x;
 	int i = memcg_stats_index(idx);
 
-	if (i < 0)
+	if (WARN_ONCE(i < 0, "%s: missing stat item %d\n", __func__, idx))
 		return 0;
 
 	x = READ_ONCE(memcg->vmstats->state_local[i]);
@@ -992,7 +995,7 @@ static void __mod_memcg_lruvec_state(struct lruvec *lruvec,
 	struct mem_cgroup *memcg;
 	int i = memcg_stats_index(idx);
 
-	if (i < 0)
+	if (WARN_ONCE(i < 0, "%s: missing stat item %d\n", __func__, idx))
 		return;
 
 	pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
@@ -1106,34 +1109,38 @@ void __mod_lruvec_kmem_state(void *p, enum node_stat_item idx, int val)
 void __count_memcg_events(struct mem_cgroup *memcg, enum vm_event_item idx,
 			  unsigned long count)
 {
-	int index = memcg_events_index(idx);
+	int i = memcg_events_index(idx);
 
-	if (mem_cgroup_disabled() || index < 0)
+	if (mem_cgroup_disabled())
+		return;
+
+	if (WARN_ONCE(i < 0, "%s: missing stat item %d\n", __func__, idx))
 		return;
 
 	memcg_stats_lock();
-	__this_cpu_add(memcg->vmstats_percpu->events[index], count);
+	__this_cpu_add(memcg->vmstats_percpu->events[i], count);
 	memcg_rstat_updated(memcg, count);
 	memcg_stats_unlock();
 }
 
 static unsigned long memcg_events(struct mem_cgroup *memcg, int event)
 {
-	int index = memcg_events_index(event);
+	int i = memcg_events_index(event);
 
-	if (index < 0)
+	if (WARN_ONCE(i < 0, "%s: missing stat item %d\n", __func__, event))
 		return 0;
-	return READ_ONCE(memcg->vmstats->events[index]);
+
+	return READ_ONCE(memcg->vmstats->events[i]);
 }
 
 static unsigned long memcg_events_local(struct mem_cgroup *memcg, int event)
 {
-	int index = memcg_events_index(event);
+	int i = memcg_events_index(event);
 
-	if (index < 0)
+	if (WARN_ONCE(i < 0, "%s: missing stat item %d\n", __func__, event))
 		return 0;
 
-	return READ_ONCE(memcg->vmstats->events_local[index]);
+	return READ_ONCE(memcg->vmstats->events_local[i]);
 }
 
 static void mem_cgroup_charge_statistics(struct mem_cgroup *memcg,
-- 
2.43.0