bpf: reparent bpf maps on memcg offlining

The memory consumed by a bpf map is always accounted to the memory
cgroup of the process which created the map. The map can outlive
the memory cgroup if it's used by processes in other cgroups or
is pinned on bpffs. In this case the map pins the original cgroup
in the dying state.

For other types of objects (slab objects, non-slab kernel allocations,
percpu objects and recently LRU pages) there is a reparenting process
implemented: on cgroup offlining charged objects are getting
reassigned to the parent cgroup. Because all charges and statistics
are fully recursive it's a fairly cheap operation.

For efficiency and consistency with other types of objects, let's do
the same for bpf maps. Fortunately thanks to the objcg API, the
required changes are minimal.

Please, note that individual allocations (slabs, percpu and large
kmallocs) already have the reparenting mechanism. This commit adds
it to the saved map->memcg pointer by replacing it to map->objcg.
Because dying cgroups are not visible for a user and all charges are
recursive, this commit doesn't bring any behavior changes for a user.

v2:
  added a missing const qualifier

Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Link: https://lore.kernel.org/r/20220711162827.184743-1-roman.gushchin@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 2b21f2a3452f..85a4db3e0536 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -221,7 +221,7 @@ struct bpf_map {
 	u32 btf_vmlinux_value_type_id;
 	struct btf *btf;
 #ifdef CONFIG_MEMCG_KMEM
-	struct mem_cgroup *memcg;
+	struct obj_cgroup *objcg;
 #endif
 	char name[BPF_OBJ_NAME_LEN];
 	struct bpf_map_off_arr *off_arr;