Re: [PATCH bpf-next v7 9/9] selftests/bpf: Add struct_ops prog private stack tests

[Tejun Heo <tj@kernel.org>]

Hello,

On Tue, Oct 29, 2024 at 03:17:23PM -0700, Yonghong Song wrote:
> The third test is the same callback function recursing itself. At run time,
> the jit trampoline recursion check kicks in to prevent the recursion.
> 
> Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
> ---
>  .../selftests/bpf/bpf_testmod/bpf_testmod.c   |  94 ++++++++++++++++
>  .../selftests/bpf/bpf_testmod/bpf_testmod.h   |   5 +
>  .../bpf/prog_tests/struct_ops_private_stack.c | 106 ++++++++++++++++++
>  .../bpf/progs/struct_ops_private_stack.c      |  62 ++++++++++
>  .../bpf/progs/struct_ops_private_stack_fail.c |  62 ++++++++++
>  .../progs/struct_ops_private_stack_recur.c    |  50 +++++++++
>  6 files changed, 379 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/struct_ops_private_stack.c
>  create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_private_stack.c
>  create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_private_stack_fail.c
>  create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_private_stack_recur.c
> 
> diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> index 8835761d9a12..eb761645551a 100644
> --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
...
> +__bpf_kfunc void bpf_testmod_ops3_call_test_1(void)
> +{
> +	st_ops3->test_1();
> +}
...
> diff --git a/tools/testing/selftests/bpf/prog_tests/struct_ops_private_stack.c b/tools/testing/selftests/bpf/prog_tests/struct_ops_private_stack.c
> new file mode 100644
> index 000000000000..4006879ca3fe
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/struct_ops_private_stack.c
...
> +static void test_private_stack_recur(void)
> +{
> +	struct struct_ops_private_stack_recur *skel;
> +	struct bpf_link *link;
> +	int err;
> +
> +	skel = struct_ops_private_stack_recur__open();
> +	if (!ASSERT_OK_PTR(skel, "struct_ops_private_stack_recur__open"))
> +		return;
> +
> +	if (skel->data->skip) {
> +		test__skip();
> +		goto cleanup;
> +	}
> +
> +	err = struct_ops_private_stack_recur__load(skel);
> +	if (!ASSERT_OK(err, "struct_ops_private_stack_recur__load"))
> +		goto cleanup;
> +
> +	link = bpf_map__attach_struct_ops(skel->maps.testmod_1);
> +	if (!ASSERT_OK_PTR(link, "attach_struct_ops"))
> +		goto cleanup;
> +
> +	ASSERT_OK(trigger_module_test_read(256), "trigger_read");
> +
> +	ASSERT_EQ(skel->bss->val_j, 3, "val_j");
> +
> +	bpf_link__destroy(link);
> +
> +cleanup:
> +	struct_ops_private_stack_recur__destroy(skel);
> +}
...
> diff --git a/tools/testing/selftests/bpf/progs/struct_ops_private_stack_recur.c b/tools/testing/selftests/bpf/progs/struct_ops_private_stack_recur.c
> new file mode 100644
> index 000000000000..15d4e914dc92
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/struct_ops_private_stack_recur.c
> @@ -0,0 +1,50 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <vmlinux.h>
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +#include "../bpf_testmod/bpf_testmod.h"
> +
> +char _license[] SEC("license") = "GPL";
> +
> +#if defined(__TARGET_ARCH_x86)
> +bool skip __attribute((__section__(".data"))) = false;
> +#else
> +bool skip = true;
> +#endif
> +
> +void bpf_testmod_ops3_call_test_1(void) __ksym;
> +
> +int val_i, val_j;
> +
> +__noinline static int subprog2(int *a, int *b)
> +{
> +	return val_i + a[10] + b[20];
> +}
> +
> +__noinline static int subprog1(int *a)
> +{
> +	/* stack size 400 bytes */
> +	int b[100] = {};
> +
> +	b[20] = 2;
> +	return subprog2(a, b);
> +}
> +
> +
> +SEC("struct_ops")
> +int BPF_PROG(test_1)
> +{
> +	/* stack size 400 bytes */
> +	int a[100] = {};
> +
> +	a[10] = 1;
> +	val_j += subprog1(a);
> +	bpf_testmod_ops3_call_test_1();
> +	return 0;
> +}
> +
> +SEC(".struct_ops")
> +struct bpf_testmod_ops3 testmod_1 = {
> +	.test_1 = (void *)test_1,
> +};

This is delta, and, while this shouldn't happen for SCX, it'd be great if
SCX can tell BPF to call a function when recursion check triggers and
ignores a call, so that SCX can trigger error, report it and eject the
scheduler.

Thanks.

-- 
tejun