On Sun, Aug 27, 2023 at 12:21 AM Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx> wrote:
>
> This Patch adds kfuncs bpf_iter_css_{new,next,destroy} which allow creation
> and manipulation of struct bpf_iter_css in open-coded iterator style. These
> kfuncs actually wrapps css_next_descendant_{pre, post}. BPF programs can
> use these kfuncs through bpf_for_each macro for iteration of all descendant
> css under a root css.
>
> Normally, css_next_descendant_{pre, post} should be called with rcu
> locking. Although we have bpf_rcu_read_lock(), here we still calls
> rcu_read_lock in bpf_iter_css_new and unlock in bpf_iter_css_destroy
> for convenience use.
>
> Signed-off-by: Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx>
> ---
> include/uapi/linux/bpf.h | 5 +++++
> kernel/bpf/helpers.c | 3 +++
> kernel/bpf/task_iter.c | 39 ++++++++++++++++++++++++++++++++++
> tools/include/uapi/linux/bpf.h | 5 +++++
> tools/lib/bpf/bpf_helpers.h | 6 ++++++
> 5 files changed, 58 insertions(+)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index cfbd527e3733..19f1f1bf9301 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -7203,4 +7203,9 @@ struct bpf_iter_process {
> __u64 __opaque[1];
> } __attribute__((aligned(8)));
>
> +struct bpf_iter_css {
> + __u64 __opaque[2];
> + char __opaque_c[1];
Burning extra 8 bytes for flags seems excessive.
Maybe let's add two iterators for descendant_post/_pre ?
The bpf prog code will be easier to read (no need to guess
what bool flag does).
> +} __attribute__((aligned(8)));
> +
> #endif /* _UAPI__LINUX_BPF_H__ */
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 81a2005edc26..47d46a51855f 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -2461,6 +2461,9 @@ BTF_ID_FLAGS(func, bpf_iter_css_task_destroy, KF_ITER_DESTROY)
> BTF_ID_FLAGS(func, bpf_iter_process_new, KF_ITER_NEW)
> BTF_ID_FLAGS(func, bpf_iter_process_next, KF_ITER_NEXT | KF_RET_NULL)
> BTF_ID_FLAGS(func, bpf_iter_process_destroy, KF_ITER_DESTROY)
> +BTF_ID_FLAGS(func, bpf_iter_css_new, KF_ITER_NEW)
> +BTF_ID_FLAGS(func, bpf_iter_css_next, KF_ITER_NEXT | KF_RET_NULL)
> +BTF_ID_FLAGS(func, bpf_iter_css_destroy, KF_ITER_DESTROY)
> BTF_ID_FLAGS(func, bpf_dynptr_adjust)
> BTF_ID_FLAGS(func, bpf_dynptr_is_null)
> BTF_ID_FLAGS(func, bpf_dynptr_is_rdonly)
> diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
> index a6717a76c1e0..ef9aef62f1ac 100644
> --- a/kernel/bpf/task_iter.c
> +++ b/kernel/bpf/task_iter.c
> @@ -893,6 +893,45 @@ __bpf_kfunc void bpf_iter_process_destroy(struct bpf_iter_process *it)
> rcu_read_unlock();
> }
>
> +struct bpf_iter_css_kern {
> + struct cgroup_subsys_state *root;
> + struct cgroup_subsys_state *pos;
> + char flag;
> +} __attribute__((aligned(8)));
> +
> +__bpf_kfunc int bpf_iter_css_new(struct bpf_iter_css *it,
> + struct cgroup_subsys_state *root, char flag)
> +{
> + struct bpf_iter_css_kern *kit = (void *)it;
> +
> + BUILD_BUG_ON(sizeof(struct bpf_iter_css_kern) != sizeof(struct bpf_iter_css));
> + BUILD_BUG_ON(__alignof__(struct bpf_iter_css_kern) != __alignof__(struct bpf_iter_css));
> + kit->root = root;
> + kit->pos = NULL;
> + kit->flag = flag;
> + rcu_read_lock();
Same request as in previous patch.
let's make bpf prog do explicit bpf_rcu_read_lock() instead.
