On Sun, Oct 22, 2023 at 8:45 AM Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> ---
> .../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;
> + 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));
You're doing this dance, because a plain cgrp pointer is not trusted?
Maybe let's add
BTF_TYPE_SAFE_RCU_OR_NULL(struct bpf_iter__cgroup) {...}
to the verifier similar to what we do for bpf_iter__task.
After if (cgrp == NULL) check the pointer is safe to iterate on.
> + 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;
> +}
> --
> 2.20.1
>
