memcg: warn for unexpected events and stats

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>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b59b670f7b7f908a91a728bf9a4660e2b562a14b..87411116ec5e62c496d3fcd946d0b70c2c77c4f2 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -670,7 +670,7 @@ 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);
@@ -686,14 +686,14 @@ 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);
@@ -922,7 +922,7 @@ 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]);
@@ -959,7 +959,10 @@ 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);
@@ -972,7 +975,7 @@ 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]);
@@ -991,7 +994,7 @@ 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);
@@ -1102,34 +1105,38 @@ 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,