[PATCH bpf-next v2 1/2] bpf: Reduce the scope of rcu_read_lock when updating fd map

[Hou Tao <houtao@xxxxxxxxxxxxxxx>]

From: Hou Tao <houtao1@xxxxxxxxxx>

There is no rcu-read-lock requirement for ops->map_fd_get_ptr() or
ops->map_fd_put_ptr(), so doesn't use rcu-read-lock for these two
callbacks and only uses rcu-read-lock for the underlying update
operations in bpf_fd_{array,htab}_map_update_elem().

Acked-by: Yonghong Song <yonghong.song@xxxxxxxxx>
Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
---
 kernel/bpf/arraymap.c | 2 ++
 kernel/bpf/hashtab.c  | 2 ++
 kernel/bpf/syscall.c  | 4 ----
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 8d365bda9a8b..6cf47bcb7b83 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -863,7 +863,9 @@ int bpf_fd_array_map_update_elem(struct bpf_map *map, struct file *map_file,
 		map->ops->map_poke_run(map, index, old_ptr, new_ptr);
 		mutex_unlock(&array->aux->poke_mutex);
 	} else {
+		rcu_read_lock();
 		old_ptr = xchg(array->ptrs + index, new_ptr);
+		rcu_read_unlock();
 	}
 
 	if (old_ptr)
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 5b9146fa825f..4c28fd51ac01 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -2523,7 +2523,9 @@ int bpf_fd_htab_map_update_elem(struct bpf_map *map, struct file *map_file,
 	if (IS_ERR(ptr))
 		return PTR_ERR(ptr);
 
+	rcu_read_lock();
 	ret = htab_map_update_elem(map, key, &ptr, map_flags);
+	rcu_read_unlock();
 	if (ret)
 		map->ops->map_fd_put_ptr(map, ptr, false);
 
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index a76467fda558..019d18d33d63 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -183,15 +183,11 @@ static int bpf_map_update_value(struct bpf_map *map, struct file *map_file,
 		err = bpf_percpu_cgroup_storage_update(map, key, value,
 						       flags);
 	} else if (IS_FD_ARRAY(map)) {
-		rcu_read_lock();
 		err = bpf_fd_array_map_update_elem(map, map_file, key, value,
 						   flags);
-		rcu_read_unlock();
 	} else if (map->map_type == BPF_MAP_TYPE_HASH_OF_MAPS) {
-		rcu_read_lock();
 		err = bpf_fd_htab_map_update_elem(map, map_file, key, value,
 						  flags);
-		rcu_read_unlock();
 	} else if (map->map_type == BPF_MAP_TYPE_REUSEPORT_SOCKARRAY) {
 		/* rcu_read_lock() is not needed */
 		err = bpf_fd_reuseport_array_update_elem(map, key, value,
-- 
2.29.2