Re: [PATCH v3] selftests/bpf: move trampoline_count to dedicated bpf_testmod target

[Mykyta Yatsenko <mykyta.yatsenko5@gmail.com>]

Sun Jian <sun.jian.kdev@gmail.com> writes:

> trampoline_count fills all trampoline attachment slots for a single
> target function and verifies that one extra attach fails with -E2BIG.
>
> It currently targets bpf_modify_return_test, which is also used by
> other selftests such as modify_return, get_func_ip_test, and
> get_func_args_test. When such tests run in parallel, they can contend
> for the same per-function trampoline quota and cause unexpected attach
> failures. This issue is currently masked by harness serialization.
>
> Move trampoline_count to a dedicated bpf_testmod target and register it
> for fmod_ret attachment. Also route the final trigger through
> trigger_module_test_read, so the execution path exercises the  same
> dedicated target.
>
> This keeps the test semantics unchanged while isolating it from other
> selftests, so it no longer needs to run in serial mode. Remove the
> TODO comment as well.
Is it really worth it just for ditching serial mode, does it improve
test_progs speed? Either way it's worth adding a comment for
bpf_testmod_trampoline_count_test() explaining that no other test should
attempt attaching to it.
>
> Tested:
>   ./test_progs -t trampoline_count -vv
>   ./test_progs -t modify_return -vv
>   ./test_progs -t get_func_ip_test -vv
>   ./test_progs -t get_func_args_test -vv
>   ./test_progs -j$(nproc) -t trampoline_count -vv
>   ./test_progs -j$(nproc) -t
>     trampoline_count,modify_return,get_func_ip_test,get_func_args_test,\
> kprobe_multi_test -vv
>   20 runs of:
>     ./test_progs -j$(nproc) -t
>     trampoline_count,modify_return,get_func_ip_test,get_func_args_test,\
> kprobe_multi_test
>
> Suggested-by: Jiri Olsa <jolsa@kernel.org>
> Signed-off-by: Sun Jian <sun.jian.kdev@gmail.com>
> ---
> Link:https://lore.kernel.org/bpf/abicUI4YQ5KkQ_Ro@mail.gmail.com/T/#m6253b7fe96fe1a4df65b274c95aac786598a9857
>
> v3:
> - route the final trigger through trigger_module_test_read() and make
>   bpf_testmod_test_read() call the dedicated trampoline_count target,
>   as suggested by Jiri
>
> v2:
> - rewrite the subject to describe the change
> - resend with the correct patch content
>
>  .../bpf/prog_tests/trampoline_count.c         | 17 ++++----------
>  .../bpf/progs/test_trampoline_count.c         |  6 ++---
>  .../selftests/bpf/test_kmods/bpf_testmod.c    | 23 +++++++++++++++++++
>  3 files changed, 30 insertions(+), 16 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/trampoline_count.c b/tools/testing/selftests/bpf/prog_tests/trampoline_count.c
> index 6cd7349d4a2b..dd2e5c84a4b5 100644
> --- a/tools/testing/selftests/bpf/prog_tests/trampoline_count.c
> +++ b/tools/testing/selftests/bpf/prog_tests/trampoline_count.c
> @@ -30,16 +30,14 @@ static struct bpf_program *load_prog(char *file, char *name, struct inst *inst)
>  	return prog;
>  }
>  
> -/* TODO: use different target function to run in concurrent mode */
> -void serial_test_trampoline_count(void)
> +void test_trampoline_count(void)
>  {
>  	char *file = "test_trampoline_count.bpf.o";
>  	char *const progs[] = { "fentry_test", "fmod_ret_test", "fexit_test" };
> -	int bpf_max_tramp_links, err, i, prog_fd;
> +	int bpf_max_tramp_links, i;
>  	struct bpf_program *prog;
>  	struct bpf_link *link;
>  	struct inst *inst;
> -	LIBBPF_OPTS(bpf_test_run_opts, opts);
>  
>  	bpf_max_tramp_links = get_bpf_max_tramp_links();
>  	if (!ASSERT_GE(bpf_max_tramp_links, 1, "bpf_max_tramp_links"))
> @@ -80,17 +78,10 @@ void serial_test_trampoline_count(void)
>  		goto cleanup;
>  
>  	/* and finally execute the probe */
> -	prog_fd = bpf_program__fd(prog);
> -	if (!ASSERT_GE(prog_fd, 0, "bpf_program__fd"))
> +	if (!ASSERT_OK(trigger_module_test_read(256),
> +		       "trigger_module_test_read"))
>  		goto cleanup;
>  
> -	err = bpf_prog_test_run_opts(prog_fd, &opts);
> -	if (!ASSERT_OK(err, "bpf_prog_test_run_opts"))
> -		goto cleanup;
> -
> -	ASSERT_EQ(opts.retval & 0xffff, 33, "bpf_modify_return_test.result");
> -	ASSERT_EQ(opts.retval >> 16, 2, "bpf_modify_return_test.side_effect");
> -
>  cleanup:
>  	for (; i >= 0; i--) {
>  		bpf_link__destroy(inst[i].link);
> diff --git a/tools/testing/selftests/bpf/progs/test_trampoline_count.c b/tools/testing/selftests/bpf/progs/test_trampoline_count.c
> index 7765720da7d5..14ad2f53cf33 100644
> --- a/tools/testing/selftests/bpf/progs/test_trampoline_count.c
> +++ b/tools/testing/selftests/bpf/progs/test_trampoline_count.c
> @@ -3,19 +3,19 @@
>  #include <bpf/bpf_helpers.h>
>  #include <bpf/bpf_tracing.h>
>  
> -SEC("fentry/bpf_modify_return_test")
> +SEC("fentry/bpf_testmod_trampoline_count_test")
>  int BPF_PROG(fentry_test, int a, int *b)
>  {
>  	return 0;
>  }
>  
> -SEC("fmod_ret/bpf_modify_return_test")
> +SEC("fmod_ret/bpf_testmod_trampoline_count_test")
>  int BPF_PROG(fmod_ret_test, int a, int *b, int ret)
>  {
>  	return 0;
>  }
>  
> -SEC("fexit/bpf_modify_return_test")
> +SEC("fexit/bpf_testmod_trampoline_count_test")
>  int BPF_PROG(fexit_test, int a, int *b, int ret)
>  {
>  	return 0;
> diff --git a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
> index e62c6b78657f..47583577e021 100644
> --- a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
> +++ b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
> @@ -470,6 +470,8 @@ noinline void bpf_testmod_stacktrace_test_1(void)
>  
>  int bpf_testmod_fentry_ok;
>  
> +noinline int bpf_testmod_trampoline_count_test(int a, int *b);
> +
>  noinline ssize_t
>  bpf_testmod_test_read(struct file *file, struct kobject *kobj,
>  		      const struct bin_attribute *bin_attr,
> @@ -548,6 +550,10 @@ bpf_testmod_test_read(struct file *file, struct kobject *kobj,
>  			21, 22, 23, 24, 25, 26) != 231)
>  		goto out;
>  
> +	i = 2;
> +	if (bpf_testmod_trampoline_count_test(1, &i) != 4 || i != 3)
> +		goto out;
> +
Do we need to add this test for the bpf_testmod_trampoline_count_test(),
if it's supposed to be used only for the trampoline count test, which
probably does not care what function actually does internally.
>  	bpf_testmod_stacktrace_test_1();
>  
>  	bpf_testmod_fentry_ok = 1;
> @@ -581,6 +587,12 @@ noinline int bpf_fentry_shadow_test(int a)
>  }
>  EXPORT_SYMBOL_GPL(bpf_fentry_shadow_test);
>  
> +noinline int bpf_testmod_trampoline_count_test(int a, int *b)
> +{
> +	*b += 1;
> +	return a + *b;
> +}
> +
>  __bpf_hook_end();
>  
>  static struct bin_attribute bin_attr_bpf_testmod_file __ro_after_init = {
> @@ -1843,6 +1855,16 @@ struct bpf_struct_ops testmod_multi_st_ops = {
>  
>  extern int bpf_fentry_test1(int a);
>  
> +BTF_KFUNCS_START(bpf_testmod_trampoline_count_ids)
> +BTF_ID_FLAGS(func, bpf_testmod_trampoline_count_test)
> +BTF_KFUNCS_END(bpf_testmod_trampoline_count_ids)
> +
> +static const struct
> +btf_kfunc_id_set bpf_testmod_trampoline_count_fmodret_set = {
> +	.owner = THIS_MODULE,
> +	.set = &bpf_testmod_trampoline_count_ids,
> +};
> +
>  static int bpf_testmod_init(void)
>  {
>  	const struct btf_id_dtor_kfunc bpf_testmod_dtors[] = {
> @@ -1859,6 +1881,7 @@ static int bpf_testmod_init(void)
>  	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &bpf_testmod_kfunc_set);
>  	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &bpf_testmod_kfunc_set);
>  	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &bpf_testmod_kfunc_set);
> +	ret = ret ?: register_btf_fmodret_id_set(&bpf_testmod_trampoline_count_fmodret_set);
>  	ret = ret ?: register_bpf_struct_ops(&bpf_bpf_testmod_ops, bpf_testmod_ops);
>  	ret = ret ?: register_bpf_struct_ops(&bpf_testmod_ops2, bpf_testmod_ops2);
>  	ret = ret ?: register_bpf_struct_ops(&bpf_testmod_ops3, bpf_testmod_ops3);
>
> base-commit: 8a30aeb0d1b4e4aaf7f7bae72f20f2ae75385ccb
> -- 
> 2.43.0