patches/old/memcg-warn-for-unexpected-events-and-stats.patch

From: Shakeel Butt <shakeel.butt@linux.dev>
Subject: memcg: warn for unexpected events and stats
Date: Wed, 1 May 2024 10:26:16 -0700

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.

Link: https://lkml.kernel.org/r/20240501172617.678560-8-shakeel.butt@linux.dev
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: T.J. Mercier <tjmercier@google.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

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

--- a/mm/memcontrol.c~memcg-warn-for-unexpected-events-and-stats
+++ a/mm/memcontrol.c
@@ -670,7 +670,7 @@ unsigned long lruvec_page_state(struct l
 		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);
@@ -686,14 +686,14 @@ unsigned long lruvec_page_state_local(st
 				      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);
@@ -922,7 +922,7 @@ unsigned long memcg_page_state(struct me
 	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]);
@@ -959,7 +959,10 @@ void __mod_memcg_state(struct mem_cgroup
 {
 	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);
@@ -972,7 +975,7 @@ static unsigned long memcg_page_state_lo
 	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]);
@@ -991,7 +994,7 @@ static void __mod_memcg_lruvec_state(str
 	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);
@@ -1102,34 +1105,38 @@ void __mod_lruvec_kmem_state(void *p, en
 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,
_