[PATCH v4 1/5] memcg: disable kmem charging in nmi for unsupported arch

[Shakeel Butt <shakeel.butt@linux.dev>]

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@linux.dev>
---
 init/Kconfig    | 7 +++++++
 mm/memcontrol.c | 3 +++
 2 files changed, 10 insertions(+)

diff --git a/init/Kconfig b/init/Kconfig
index 4cdd1049283c..a2aa49cfb8bd 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1006,6 +1006,13 @@ config MEMCG
 	help
 	  Provides control over the memory footprint of tasks in a cgroup.
 
+config MEMCG_NMI_UNSAFE
+	bool
+	depends on MEMCG
+	depends on HAVE_NMI
+	depends on !ARCH_HAS_NMI_SAFE_THIS_CPU_OPS && !ARCH_HAVE_NMI_SAFE_CMPXCHG
+	default y
+
 config MEMCG_V1
 	bool "Legacy cgroup v1 memory controller"
 	depends on MEMCG
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e17b698f6243..532e2c06ea60 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2652,6 +2652,9 @@ __always_inline struct obj_cgroup *current_obj_cgroup(void)
 	struct mem_cgroup *memcg;
 	struct obj_cgroup *objcg;
 
+	if (IS_ENABLED(CONFIG_MEMCG_NMI_UNSAFE) && in_nmi())
+		return NULL;
+
 	if (in_task()) {
 		memcg = current->active_memcg;
 		if (unlikely(memcg))
-- 
2.47.1