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Date:   Fri, 28 Apr 2023 09:32:01 -0700
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Subject: Re: [PATCH bpf-next v4 2/2] selftests/bpf: Add testcase for
 bpf_task_under_cgroup
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To:     Feng zhou <zhoufeng.zf@bytedance.com>, martin.lau@linux.dev,
        ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org,
        song@kernel.org, yhs@fb.com, john.fastabend@gmail.com,
        kpsingh@kernel.org, sdf@google.com, haoluo@google.com,
        jolsa@kernel.org, davem@davemloft.net, edumazet@google.com,
        kuba@kernel.org, pabeni@redhat.com, mykolal@fb.com,
        shuah@kernel.org
Cc:     bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org, linux-kselftest@vger.kernel.org,
        yangzhenze@bytedance.com, wangdongdong.6@bytedance.com
References: <20230428071737.43849-1-zhoufeng.zf@bytedance.com>
 <20230428071737.43849-3-zhoufeng.zf@bytedance.com>
From:   Yonghong Song <yhs@meta.com>
In-Reply-To: <20230428071737.43849-3-zhoufeng.zf@bytedance.com>
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On 4/28/23 12:17 AM, Feng zhou wrote:
> From: Feng Zhou <zhoufeng.zf@bytedance.com>
> 
> test_progs:
> Tests new kfunc bpf_task_under_cgroup().
> 
> The bpf program saves the new task's pid within a given cgroup to
> the remote_pid, which is convenient for the user-mode program to
> verify the test correctness.
> 
> The user-mode program creates its own mount namespace, and mounts the
> cgroupsv2 hierarchy in there, call the fork syscall, then check if
> remote_pid and local_pid are unequal.
> 
> Signed-off-by: Feng Zhou <zhoufeng.zf@bytedance.com>

Ack with a few nits below.

Acked-by: Yonghong Song <yhs@fb.com>

> ---
>   tools/testing/selftests/bpf/DENYLIST.s390x    |  1 +
>   .../bpf/prog_tests/task_under_cgroup.c        | 55 +++++++++++++++++++
>   .../bpf/progs/test_task_under_cgroup.c        | 51 +++++++++++++++++
>   3 files changed, 107 insertions(+)
>   create mode 100644 tools/testing/selftests/bpf/prog_tests/task_under_cgroup.c
>   create mode 100644 tools/testing/selftests/bpf/progs/test_task_under_cgroup.c
> 
> diff --git a/tools/testing/selftests/bpf/DENYLIST.s390x b/tools/testing/selftests/bpf/DENYLIST.s390x
> index c7463f3ec3c0..5061d9e24c16 100644
> --- a/tools/testing/selftests/bpf/DENYLIST.s390x
> +++ b/tools/testing/selftests/bpf/DENYLIST.s390x
> @@ -26,3 +26,4 @@ user_ringbuf                             # failed to find kernel BTF type ID of
>   verif_stats                              # trace_vprintk__open_and_load unexpected error: -9                           (?)
>   xdp_bonding                              # failed to auto-attach program 'trace_on_entry': -524                        (trampoline)
>   xdp_metadata                             # JIT does not support calling kernel function                                (kfunc)
> +test_task_under_cgroup                   # JIT does not support calling kernel function                                (kfunc)
> diff --git a/tools/testing/selftests/bpf/prog_tests/task_under_cgroup.c b/tools/testing/selftests/bpf/prog_tests/task_under_cgroup.c
> new file mode 100644
> index 000000000000..5e79dff86dec
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/task_under_cgroup.c
> @@ -0,0 +1,55 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2023 Bytedance */
> +
> +#include <sys/syscall.h>
> +#include <test_progs.h>
> +#include <cgroup_helpers.h>
> +#include "test_task_under_cgroup.skel.h"
> +
> +#define FOO	"/foo"
> +
> +void test_task_under_cgroup(void)
> +{
> +	struct test_task_under_cgroup *skel;
> +	int ret, foo = -1;
> +	pid_t pid;
> +
> +	foo = test__join_cgroup(FOO);
> +	if (!ASSERT_OK(foo < 0, "cgroup_join_foo"))
> +		return;
> +
> +	skel = test_task_under_cgroup__open();
> +	if (!ASSERT_OK_PTR(skel, "test_task_under_cgroup__open"))
> +		goto cleanup;
> +
> +	skel->rodata->local_pid = getpid();
> +	skel->bss->remote_pid = getpid();
> +	skel->rodata->cgid = get_cgroup_id(FOO);
> +
> +	ret = test_task_under_cgroup__load(skel);
> +	if (!ASSERT_OK(ret, "test_task_under_cgroup__load"))
> +		goto cleanup;
> +
> +	ret = test_task_under_cgroup__attach(skel);
> +	if (!ASSERT_OK(ret, "test_task_under_cgroup__attach"))
> +		goto cleanup;
> +
> +	pid = fork();
> +	if (pid == 0)
> +		exit(0);
> +	else if (pid == -1)
> +		printf("Couldn't fork process!\n");

ASSERT_* is preferred compared to 'printf'. Maybe ASSERT_TRUE(0, 
"Couldn't fork process")?

> +
> +	wait(NULL);
> +
> +	test_task_under_cgroup__detach(skel);
> +
> +	ASSERT_NEQ(skel->bss->remote_pid, skel->rodata->local_pid,
> +		   "test task_under_cgroup");
> +
> +cleanup:
> +	if (foo >= 0)

"if (foo >= 0)" is not needed. 'foo' is guaranteed ">= 0" as this point.

> +		close(foo);
> +
> +	test_task_under_cgroup__destroy(skel);
> +}
> diff --git a/tools/testing/selftests/bpf/progs/test_task_under_cgroup.c b/tools/testing/selftests/bpf/progs/test_task_under_cgroup.c
> new file mode 100644
> index 000000000000..5bcb726d6d0a
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_task_under_cgroup.c
> @@ -0,0 +1,51 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2023 Bytedance */
> +
> +#include <vmlinux.h>
> +#include <bpf/bpf_tracing.h>
> +#include <bpf/bpf_helpers.h>
> +
> +#include "bpf_misc.h"
> +
> +struct cgroup *bpf_cgroup_from_id(u64 cgid) __ksym;
> +long bpf_task_under_cgroup(struct task_struct *task, struct cgroup *ancestor) __ksym;
> +void bpf_cgroup_release(struct cgroup *p) __ksym;
> +struct task_struct *bpf_task_acquire(struct task_struct *p) __ksym;
> +void bpf_task_release(struct task_struct *p) __ksym;
> +
> +const volatile int local_pid;
> +const volatile long cgid;

cgid cannot be a negative number. So let us do
const volatile __u64 cgid;

> +int remote_pid;
> +
> +SEC("tp_btf/task_newtask")
> +int BPF_PROG(handle__task_newtask, struct task_struct *task, u64 clone_flags)
> +{
> +	struct cgroup *cgrp = NULL;
> +	struct task_struct *acquired = NULL;

"acquired = NULL" is not needed. Just do "struct task_struct *acquired;".

> +
> +	if (local_pid != (bpf_get_current_pid_tgid() >> 32))
> +		return 0;
> +
> +	acquired = bpf_task_acquire(task);
> +	if (!acquired)
> +		return 0;
> +
> +	if (local_pid == acquired->tgid)
> +		goto out;
> +
> +	cgrp = bpf_cgroup_from_id(cgid);
> +	if (!cgrp)
> +		goto out;
> +
> +	if (bpf_task_under_cgroup(acquired, cgrp))
> +		remote_pid = acquired->tgid;
> +
> +out:
> +	if (acquired)
> +		bpf_task_release(acquired);
> +	if (cgrp)
> +		bpf_cgroup_release(cgrp);
> +	return 0;
> +}
> +
> +char _license[] SEC("license") = "GPL";