Commit 8f82583f authored Dec 14, 2023 by Hou Tao Committed by Alexei Starovoitov Dec 13, 2023

bpf: Reduce the scope of rcu_read_lock when updating fd map



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.

For bpf_fd_array_map_update_elem(), accessing array->ptrs doesn't need
rcu-read-lock because array->ptrs must still be allocated. For
bpf_fd_htab_map_update_elem(), htab_map_update_elem() only requires
rcu-read-lock to be held to avoid the WARN_ON_ONCE(), so only use
rcu_read_lock() during the invocation of htab_map_update_elem().

Acked-by: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20231214043010.3458072-2-houtao@huaweicloud.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>

parent 2a0c6b41

kernel/bpf/hashtab.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -2523,7 +2523,13 @@ int bpf_fd_htab_map_update_elem(struct bpf_map map, struct file map_file,
		if (IS_ERR(ptr))
		return PTR_ERR(ptr);

		/* The htab bucket lock is always held during update operations in fd
		* htab map, and the following rcu_read_lock() is only used to avoid
		* the WARN_ON_ONCE in htab_map_update_elem().
		*/
		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);

kernel/bpf/syscall.c

+0 −4

Original line number	Diff line number	Diff line
		@@ -184,15 +184,11 @@ 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,