memcg: add nmi-safe update for MEMCG_KMEM

The objcg based kmem charging and uncharging code path needs to update
MEMCG_KMEM appropriately.  Let's add support to update MEMCG_KMEM in
nmi-safe way for those code paths.

Link: https://lkml.kernel.org/r/20250519063142.111219-4-shakeel.butt@linux.dev
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e8e8bec..74bb19f 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2715,6 +2715,23 @@ struct obj_cgroup *get_obj_cgroup_from_folio(struct folio *folio)
        return objcg;
 }
 
+#ifdef CONFIG_MEMCG_NMI_SAFETY_REQUIRES_ATOMIC
+static inline void account_kmem_nmi_safe(struct mem_cgroup *memcg, int val)
+{
+       if (likely(!in_nmi())) {
+               mod_memcg_state(memcg, MEMCG_KMEM, val);
+       } else {
+               /* TODO: add to cgroup update tree once it is nmi-safe. */
+               atomic_add(val, &memcg->kmem_stat);
+       }
+}
+#else
+static inline void account_kmem_nmi_safe(struct mem_cgroup *memcg, int val)
+{
+       mod_memcg_state(memcg, MEMCG_KMEM, val);
+}
+#endif
+
 /*
  * obj_cgroup_uncharge_pages: uncharge a number of kernel pages from a objcg
  * @objcg: object cgroup to uncharge
@@ -2727,7 +2744,7 @@ static void obj_cgroup_uncharge_pages(struct obj_cgroup *objcg,
 
        memcg = get_mem_cgroup_from_objcg(objcg);
 
-       mod_memcg_state(memcg, MEMCG_KMEM, -nr_pages);
+       account_kmem_nmi_safe(memcg, -nr_pages);
        memcg1_account_kmem(memcg, -nr_pages);
        if (!mem_cgroup_is_root(memcg))
                refill_stock(memcg, nr_pages);
@@ -2755,7 +2772,7 @@ static int obj_cgroup_charge_pages(struct obj_cgroup *objcg, gfp_t gfp,
        if (ret)
                goto out;
 
-       mod_memcg_state(memcg, MEMCG_KMEM, nr_pages);
+       account_kmem_nmi_safe(memcg, nr_pages);
        memcg1_account_kmem(memcg, nr_pages);
 out:
        css_put(&memcg->css);