[PATCH v3 1/5] memcg: disable kmem charging in nmi for unsupported arch

[Shakeel Butt]

The memcg accounting and stats uses this_cpu* and atomic* ops. There are
archs which define CONFIG_HAVE_NMI but does not define
CONFIG_ARCH_HAS_NMI_SAFE_THIS_CPU_OPS and ARCH_HAVE_NMI_SAFE_CMPXCHG, so
memcg accounting for such archs in nmi context is not possible to
support. Let's just disable memcg accounting in nmi context for such
archs.

Signed-off-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
---
Changes since v2:
- reorder the in_nmi() check as suggested by Vlastimil

 include/linux/memcontrol.h |  5 +++++
 mm/memcontrol.c            | 15 +++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index f7848f73f41c..53920528821f 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -62,6 +62,11 @@ struct mem_cgroup_reclaim_cookie {
 
 #ifdef CONFIG_MEMCG
 
+#if defined(CONFIG_ARCH_HAS_NMI_SAFE_THIS_CPU_OPS) || \
+	!defined(CONFIG_HAVE_NMI) || defined(ARCH_HAVE_NMI_SAFE_CMPXCHG)
+#define MEMCG_SUPPORTS_NMI_CHARGING
+#endif
+
 #define MEM_CGROUP_ID_SHIFT	16
 
 struct mem_cgroup_id {
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e17b698f6243..0f182e4a9da0 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2647,11 +2647,26 @@ static struct obj_cgroup *current_objcg_update(void)
 	return objcg;
 }
 
+#ifdef MEMCG_SUPPORTS_NMI_CHARGING
+static inline bool nmi_charging_allowed(void)
+{
+	return true;
+}
+#else
+static inline bool nmi_charging_allowed(void)
+{
+	return false;
+}
+#endif
+
 __always_inline struct obj_cgroup *current_obj_cgroup(void)
 {
 	struct mem_cgroup *memcg;
 	struct obj_cgroup *objcg;
 
+	if (!nmi_charging_allowed() && in_nmi())
+		return NULL;
+
 	if (in_task()) {
 		memcg = current->active_memcg;
 		if (unlikely(memcg))
-- 
2.47.1