Re: [PATCH bpf-next v7 2/4] selftests/bpf: Add test for recursive attachment of tracing progs

[Jiri Olsa <olsajiri@gmail.com>]

On Fri, Dec 08, 2023 at 07:55:54PM +0100, Dmitrii Dolgov wrote:
> Verify the fact that only one fentry prog could be attached to another
> fentry, building up an attachment chain of limited size. Use existing
> bpf_testmod as a start of the chain.
> 
> Signed-off-by: Dmitrii Dolgov <9erthalion6@gmail.com>
> ---
> Changes in v5:
>     - Test only one level of attachment
> 
>  .../bpf/prog_tests/recursive_attach.c         | 69 +++++++++++++++++++
>  .../selftests/bpf/progs/fentry_recursive.c    | 19 +++++
>  .../bpf/progs/fentry_recursive_target.c       | 20 ++++++
>  3 files changed, 108 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/recursive_attach.c
>  create mode 100644 tools/testing/selftests/bpf/progs/fentry_recursive.c
>  create mode 100644 tools/testing/selftests/bpf/progs/fentry_recursive_target.c
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/recursive_attach.c b/tools/testing/selftests/bpf/prog_tests/recursive_attach.c
> new file mode 100644
> index 000000000000..7248d0661ee9
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/recursive_attach.c
> @@ -0,0 +1,69 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2023 Red Hat, Inc. */
> +#include <test_progs.h>
> +#include "fentry_recursive.skel.h"
> +#include "fentry_recursive_target.skel.h"
> +#include <bpf/btf.h>
> +#include "bpf/libbpf_internal.h"
> +
> +/*
> + * Test following scenarios:
> + * - attach one fentry progs to another one
> + * - more than one nesting levels are not allowed
> + */
> +void test_recursive_fentry_attach(void)
> +{
> +	struct fentry_recursive_target *target_skel = NULL;
> +	struct fentry_recursive *tracing_chain[2] = {};
> +	struct bpf_program *prog;
> +	int prev_fd, err;
> +
> +	target_skel = fentry_recursive_target__open_and_load();
> +	if (!ASSERT_OK_PTR(target_skel, "fentry_recursive_target__open_and_load"))
> +		goto close_prog;
> +
> +	/* Create an attachment chain with two fentry progs */
> +	for (int i = 0; i < 2; i++) {
> +		tracing_chain[i] = fentry_recursive__open();
> +		if (!ASSERT_OK_PTR(tracing_chain[i], "fentry_recursive__open"))
> +			goto close_prog;
> +
> +		/*
> +		 * The first prog in the chain is going to be attached to the target
> +		 * fentry program, the second one to the previous in the chain.
> +		 */
> +		if (i == 0) {
> +			prog = tracing_chain[0]->progs.recursive_attach;
> +			prev_fd = bpf_program__fd(target_skel->progs.test1);
> +			err = bpf_program__set_attach_target(prog, prev_fd, "test1");
> +		} else {
> +			prog = tracing_chain[i]->progs.recursive_attach;

nit, common line, could be placed before the loop

perhaps also the bpf_program__set_attach_target call does not need to be
in the if path, I think it should work with NULL for attach_func_name as
long as we provide attach_prog_fd

I wonder now with just 2 skels the test might be easier to read
without the loop, but I dont have strong opinion about that

> +			prev_fd = bpf_program__fd(tracing_chain[i-1]->progs.recursive_attach);
> +			err = bpf_program__set_attach_target(prog, prev_fd, "recursive_attach");
> +		}
> +
> +		if (!ASSERT_OK(err, "bpf_program__set_attach_target"))
> +			goto close_prog;
> +
> +		err = fentry_recursive__load(tracing_chain[i]);
> +		/* The first attach should succeed, the second fail */
> +		if (i == 0) {
> +			if (!ASSERT_OK(err, "fentry_recursive__load"))
> +				goto close_prog;
> +
> +			err = fentry_recursive__attach(tracing_chain[i]);
> +			if (!ASSERT_OK(err, "fentry_recursive__attach"))
> +				goto close_prog;
> +		} else {
> +			if (!ASSERT_ERR(err, "fentry_recursive__load"))
> +				goto close_prog;
> +		}
> +	}
> +
> +close_prog:
> +	fentry_recursive_target__destroy(target_skel);
> +	for (int i = 0; i < 2; i++) {
> +		if (tracing_chain[i])
> +			fentry_recursive__destroy(tracing_chain[i]);
> +	}
> +}
> diff --git a/tools/testing/selftests/bpf/progs/fentry_recursive.c b/tools/testing/selftests/bpf/progs/fentry_recursive.c
> new file mode 100644
> index 000000000000..1df490230344
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/fentry_recursive.c
> @@ -0,0 +1,19 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2023 Red Hat, Inc. */
> +#include <linux/bpf.h>
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +char _license[] SEC("license") = "GPL";
> +
> +__u64 test1_result = 0;

there's no reason to keep test1_result in here, please remove

> +
> +/*
> + * Dummy fentry bpf prog for testing fentry attachment chains
> + */
> +SEC("fentry/XXX")
> +int BPF_PROG(recursive_attach, int a)
> +{
> +	test1_result = a == 1;
> +	return 0;
> +}
> diff --git a/tools/testing/selftests/bpf/progs/fentry_recursive_target.c b/tools/testing/selftests/bpf/progs/fentry_recursive_target.c
> new file mode 100644
> index 000000000000..b6fb8ebd598d
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/fentry_recursive_target.c
> @@ -0,0 +1,20 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2023 Red Hat, Inc. */
> +#include <linux/bpf.h>
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +char _license[] SEC("license") = "GPL";
> +
> +__u64 test1_result = 0;

ditto

thanks,
jirka

> +
> +/*
> + * Dummy fentry bpf prog for testing fentry attachment chains. It's going to be
> + * a start of the chain.
> + */
> +SEC("fentry/bpf_testmod_fentry_test1")
> +int BPF_PROG(test1, int a)
> +{
> +	test1_result = a == 1;
> +	return 0;
> +}
> -- 
> 2.41.0
>