Re: [PATCH bpf-next v3 2/3] selftests/bpf: Add tests for css_task iter combining with cgroup iter

[Yonghong Song <yonghong.song@linux.dev>]

On 10/25/23 12:59 AM, Chuyi Zhou wrote:
> This patch adds a test which demonstrates how css_task iter can be combined
> with cgroup iter and it won't cause deadlock, though cgroup iter is not
> sleepable.
>
> Signed-off-by: Chuyi Zhou <zhouchuyi@bytedance.com>

Ack with a few nits below:

Acked-by: Yonghong Song <yonghong.song@linux.dev>


> ---
>   .../selftests/bpf/prog_tests/cgroup_iter.c    | 33 +++++++++++++++
>   .../selftests/bpf/progs/iters_css_task.c      | 41 +++++++++++++++++++
>   2 files changed, 74 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/cgroup_iter.c b/tools/testing/selftests/bpf/prog_tests/cgroup_iter.c
> index e02feb5fae97..3679687a6927 100644
> --- a/tools/testing/selftests/bpf/prog_tests/cgroup_iter.c
> +++ b/tools/testing/selftests/bpf/prog_tests/cgroup_iter.c
> @@ -4,6 +4,7 @@
>   #include <test_progs.h>
>   #include <bpf/libbpf.h>
>   #include <bpf/btf.h>
> +#include "iters_css_task.skel.h"
>   #include "cgroup_iter.skel.h"
>   #include "cgroup_helpers.h"
>   
> @@ -263,6 +264,35 @@ static void test_walk_dead_self_only(struct cgroup_iter *skel)
>   	close(cgrp_fd);
>   }
>   
> +static void test_walk_self_only_css_task(void)
> +{
> +	struct iters_css_task *skel = NULL;

'= NULL' is unnecessary.

> +	int err;
> +
> +	skel = iters_css_task__open();
> +	if (!ASSERT_OK_PTR(skel, "skel_open"))
> +		return;
> +
> +	bpf_program__set_autoload(skel->progs.cgroup_id_printer, true);
> +
> +	err = iters_css_task__load(skel);
> +	if (!ASSERT_OK(err, "skel_load"))
> +		goto cleanup;
> +
> +	err = join_cgroup(cg_path[CHILD2]);
> +	if (!ASSERT_OK(err, "join_cgroup"))
> +		goto cleanup;
> +
> +	skel->bss->target_pid = getpid();
> +	snprintf(expected_output, sizeof(expected_output),
> +		PROLOGUE "%8llu\n" EPILOGUE, cg_id[CHILD2]);
> +	read_from_cgroup_iter(skel->progs.cgroup_id_printer, cg_fd[CHILD2],
> +		BPF_CGROUP_ITER_SELF_ONLY, "test_walk_self_only_css_task");
> +	ASSERT_EQ(skel->bss->css_task_cnt, 1, "css_task_cnt");
> +cleanup:
> +	iters_css_task__destroy(skel);
> +}
> +
>   void test_cgroup_iter(void)
>   {
>   	struct cgroup_iter *skel = NULL;
> @@ -293,6 +323,9 @@ void test_cgroup_iter(void)
>   		test_walk_self_only(skel);
>   	if (test__start_subtest("cgroup_iter__dead_self_only"))
>   		test_walk_dead_self_only(skel);
> +	if (test__start_subtest("cgroup_iter__self_only_css_task"))
> +		test_walk_self_only_css_task();
> +
>   out:
>   	cgroup_iter__destroy(skel);
>   	cleanup_cgroups();
> diff --git a/tools/testing/selftests/bpf/progs/iters_css_task.c b/tools/testing/selftests/bpf/progs/iters_css_task.c
> index 5089ce384a1c..0974e6f44328 100644
> --- a/tools/testing/selftests/bpf/progs/iters_css_task.c
> +++ b/tools/testing/selftests/bpf/progs/iters_css_task.c
> @@ -10,6 +10,7 @@
>   
>   char _license[] SEC("license") = "GPL";
>   
> +struct cgroup *bpf_cgroup_acquire(struct cgroup *p) __ksym;
>   struct cgroup *bpf_cgroup_from_id(u64 cgid) __ksym;
>   void bpf_cgroup_release(struct cgroup *p) __ksym;
>   
> @@ -45,3 +46,43 @@ int BPF_PROG(iter_css_task_for_each, struct vm_area_struct *vma,
>   
>   	return -EPERM;
>   }
> +
> +static inline u64 cgroup_id(struct cgroup *cgrp)
> +{
> +	return cgrp->kn->id;
> +}
> +
> +SEC("?iter/cgroup")
> +int cgroup_id_printer(struct bpf_iter__cgroup *ctx)
> +{
> +	struct seq_file *seq = ctx->meta->seq;
> +	struct cgroup *cgrp, *acquired;
> +	struct cgroup_subsys_state *css;
> +	struct task_struct *task;
> +
> +	cgrp = ctx->cgroup;
> +
> +	/* epilogue */
> +	if (cgrp == NULL) {
> +		BPF_SEQ_PRINTF(seq, "epilogue\n");
> +		return 0;
> +	}
> +
> +	/* prologue */
> +	if (ctx->meta->seq_num == 0)
> +		BPF_SEQ_PRINTF(seq, "prologue\n");
> +
> +	BPF_SEQ_PRINTF(seq, "%8llu\n", cgroup_id(cgrp));
> +
> +	acquired = bpf_cgroup_from_id(cgroup_id(cgrp));

cgroup_id(cgrp) needs only one call.

> +	if (!acquired)
> +		return 0;
> +	css = &acquired->self;
> +	css_task_cnt = 0;
> +	bpf_for_each(css_task, task, css, CSS_TASK_ITER_PROCS) {
> +		if (task->pid == target_pid)
> +			css_task_cnt++;
> +	}
> +	bpf_cgroup_release(acquired);
> +	return 0;
> +}