Re: [PATCH bpf-next 2/2] selftests/bpf: Add testcase for updating attached freplace prog to PROG_ARRAY map

[Yonghong Song <yonghong.song@linux.dev>]

On 7/24/24 5:32 PM, Leon Hwang wrote:
> Add a selftest to confirm the issue, which gets -EINVAL when update
> attached freplace prog to PROG_ARRAY map, has been fixed.
>
> cd tools/testing/selftests/bpf; ./test_progs -t tailcalls
> 327/25  tailcalls/tailcall_freplace:OK
> 327     tailcalls:OK
> Summary: 1/25 PASSED, 0 SKIPPED, 0 FAILED
>
> Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
> ---
>   .../selftests/bpf/prog_tests/tailcalls.c      | 76 ++++++++++++++++++-
>   .../selftests/bpf/progs/tailcall_freplace.c   | 33 ++++++++
>   .../testing/selftests/bpf/progs/tc_bpf2bpf.c  | 23 ++++++
>   3 files changed, 131 insertions(+), 1 deletion(-)
>   create mode 100644 tools/testing/selftests/bpf/progs/tailcall_freplace.c
>   create mode 100644 tools/testing/selftests/bpf/progs/tc_bpf2bpf.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/tailcalls.c b/tools/testing/selftests/bpf/prog_tests/tailcalls.c
> index e01fabb8cc415..f1145601c0005 100644
> --- a/tools/testing/selftests/bpf/prog_tests/tailcalls.c
> +++ b/tools/testing/selftests/bpf/prog_tests/tailcalls.c
> @@ -5,7 +5,8 @@
>   #include "tailcall_poke.skel.h"
>   #include "tailcall_bpf2bpf_hierarchy2.skel.h"
>   #include "tailcall_bpf2bpf_hierarchy3.skel.h"
> -
> +#include "tailcall_freplace.skel.h"
> +#include "tc_bpf2bpf.skel.h"
>   
>   /* test_tailcall_1 checks basic functionality by patching multiple locations
>    * in a single program for a single tail call slot with nop->jmp, jmp->nop
> @@ -1495,6 +1496,77 @@ static void test_tailcall_bpf2bpf_hierarchy_3(void)
>   	RUN_TESTS(tailcall_bpf2bpf_hierarchy3);
>   }
>   
> +/* test_tailcall_freplace checks that the attached freplace prog is OK to
> + * update to PROG_ARRAY map.

update the prog_array map.

> + */
> +static void test_tailcall_freplace(void)
> +{
> +	struct tailcall_freplace *fr_skel = NULL;
> +	struct tc_bpf2bpf *tc_skel = NULL;
> +	struct bpf_link *fr_link = NULL;
> +	int prog_fd, map_fd;
> +	char buff[128] = {};
> +	int err, key;
> +
> +	LIBBPF_OPTS(bpf_test_run_opts, topts,
> +		    .data_in = buff,
> +		    .data_size_in = sizeof(buff),
> +		    .repeat = 1,
> +	);
> +
> +	fr_skel = tailcall_freplace__open();
> +	if (!ASSERT_OK_PTR(fr_skel, "open fr_skel"))

if (!ASSERT_OK_PTR(fr_skel, "open fr_skel"))
==>
if (!ASSERT_OK_PTR(fr_skel, "tailcall_freplace__open"))
Similar for below other ASSERT_* macros.

> +		goto out;

Let us just do 'return' here.

> +
> +	tc_skel = tc_bpf2bpf__open_and_load();
> +	if (!ASSERT_OK_PTR(tc_skel, "open tc_skel"))
> +		goto out;
> +
> +	prog_fd = bpf_program__fd(tc_skel->progs.entry);
> +	if (!ASSERT_GE(prog_fd, 0, "tc_skel entry prog_id"))
> +		goto out;

ASSERT_GE is not necessary, prog_fd should already be valid.

> +
> +	err = bpf_program__set_attach_target(fr_skel->progs.entry,
> +					     prog_fd, "subprog");
> +	if (!ASSERT_OK(err, "set_attach_target"))
> +		goto out;
> +
> +	err = tailcall_freplace__load(fr_skel);
> +	if (!ASSERT_OK(err, "load fr_skel"))
> +		goto out;
> +
> +	fr_link = bpf_program__attach_freplace(fr_skel->progs.entry,
> +					       prog_fd, "subprog");
> +	if (!ASSERT_OK_PTR(fr_link, "attach_freplace"))
> +		goto out;
> +
> +	prog_fd = bpf_program__fd(fr_skel->progs.entry);
> +	if (!ASSERT_GE(prog_fd, 0, "fr_skel entry prog_fd"))
> +		goto out;

prog_fd is valid here. No need ASSERT_GE.

> +
> +	map_fd = bpf_map__fd(fr_skel->maps.jmp_table);
> +	if (!ASSERT_GE(map_fd, 0, "fr_skel jmp_table map_fd"))
> +		goto out;

map_fd is valid. No need ASSERT_GE.

> +
> +	key = 0;
> +	err = bpf_map_update_elem(map_fd, &key, &prog_fd, BPF_ANY);
> +	if (!ASSERT_OK(err, "update jmp_table"))
> +		goto out;
> +
> +	prog_fd = bpf_program__fd(tc_skel->progs.entry);
> +	if (!ASSERT_GE(prog_fd, 0, "prog_fd"))
> +		goto out;

prog_fd is valid here.

> +
> +	err = bpf_prog_test_run_opts(prog_fd, &topts);
> +	ASSERT_OK(err, "test_run");
> +	ASSERT_EQ(topts.retval, 34, "test_run retval");
> +
> +out:
> +	bpf_link__destroy(fr_link);
> +	tc_bpf2bpf__destroy(tc_skel);
> +	tailcall_freplace__destroy(fr_skel);
> +}
> +
>   void test_tailcalls(void)
>   {
>   	if (test__start_subtest("tailcall_1"))
> @@ -1543,4 +1615,6 @@ void test_tailcalls(void)
>   		test_tailcall_bpf2bpf_hierarchy_fentry_entry();
>   	test_tailcall_bpf2bpf_hierarchy_2();
>   	test_tailcall_bpf2bpf_hierarchy_3();
> +	if (test__start_subtest("tailcall_freplace"))
> +		test_tailcall_freplace();
>   }
> diff --git a/tools/testing/selftests/bpf/progs/tailcall_freplace.c b/tools/testing/selftests/bpf/progs/tailcall_freplace.c
> new file mode 100644
> index 0000000000000..80b5fa386ed9c
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/tailcall_freplace.c
> @@ -0,0 +1,33 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/bpf.h>
> +#include <bpf/bpf_helpers.h>
> +#include "bpf_legacy.h"

bpf_legacy.h is not needed.

> +
> +struct {
> +	__uint(type, BPF_MAP_TYPE_PROG_ARRAY);
> +	__uint(max_entries, 1);
> +	__uint(key_size, sizeof(__u32));
> +	__uint(value_size, sizeof(__u32));
> +} jmp_table SEC(".maps");
> +
> +int count = 0;
> +
> +__noinline
> +int subprog(struct __sk_buff *skb)
> +{
> +	count++;
> +
> +	bpf_tail_call_static(skb, &jmp_table, 0);
> +
> +	return count;
> +}

subprog() can be inlined into entry(). This
can avoid confusing vs. tc_bpf2bpf.c.

Better if you can differentiate two 'entry()' function
names, e.g., entry_freplace(), entry_tc(), it can make
it easy for people to understand your change in tailcalls.c.

> +
> +SEC("freplace")
> +int entry(struct __sk_buff *skb)
> +{
> +	return subprog(skb);
> +}
> +
> +char __license[] SEC("license") = "GPL";
> +
> diff --git a/tools/testing/selftests/bpf/progs/tc_bpf2bpf.c b/tools/testing/selftests/bpf/progs/tc_bpf2bpf.c
> new file mode 100644
> index 0000000000000..4810961554585
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/tc_bpf2bpf.c
> @@ -0,0 +1,23 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/bpf.h>
> +#include <bpf/bpf_helpers.h>
> +#include "bpf_legacy.h"
> +
> +__noinline
> +int subprog(struct __sk_buff *skb)
> +{
> +	volatile int ret = 1;
> +
> +	asm volatile (""::"r+"(ret));
> +	return ret;
> +}
> +
> +SEC("tc")
> +int entry(struct __sk_buff *skb)
> +{
> +	return subprog(skb);
> +}
> +
> +char __license[] SEC("license") = "GPL";
> +