Re: [PATCHv3 bpf 2/2] selftests/bpf: Add test for early update in prog_array_map_poke_run

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

On 12/3/23 3:48 PM, Jiri Olsa wrote:
> Adding test that tries to trigger the BUG_ON during early map update
> in prog_array_map_poke_run function.
>
> The idea is to share prog array map between thread that constantly
> updates it and another one loading a program that uses that prog
> array.
>
> Eventually we will hit a place where the program is ok to be updated
> (poke->tailcall_target_stable check) but the address is still not
> registered in kallsyms, so the bpf_arch_text_poke returns -EINVAL
> and cause imbalance for the next tail call update check, which will
> fail with -EBUSY in bpf_arch_text_poke as described in previous fix.
>
> Acked-by: Ilya Leoshkevich <iii@linux.ibm.com>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
>   .../selftests/bpf/prog_tests/tailcall_poke.c  | 74 +++++++++++++++++++
>   .../selftests/bpf/progs/tailcall_poke.c       | 32 ++++++++
>   2 files changed, 106 insertions(+)
>   create mode 100644 tools/testing/selftests/bpf/prog_tests/tailcall_poke.c
>   create mode 100644 tools/testing/selftests/bpf/progs/tailcall_poke.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/tailcall_poke.c b/tools/testing/selftests/bpf/prog_tests/tailcall_poke.c
> new file mode 100644
> index 000000000000..f7e2c09fd772
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/tailcall_poke.c
> @@ -0,0 +1,74 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <unistd.h>
> +#include <test_progs.h>
> +#include "tailcall_poke.skel.h"
> +
> +#define JMP_TABLE "/sys/fs/bpf/jmp_table"
> +
> +static int thread_exit;
> +
> +static void *update(void *arg)
> +{
> +	__u32 zero = 0, prog1_fd, prog2_fd, map_fd;
> +	struct tailcall_poke *call = arg;
> +
> +	map_fd = bpf_map__fd(call->maps.jmp_table);
> +	prog1_fd = bpf_program__fd(call->progs.call1);
> +	prog2_fd = bpf_program__fd(call->progs.call2);
> +
> +	while (!thread_exit) {
> +		bpf_map_update_elem(map_fd, &zero, &prog1_fd, BPF_ANY);
> +		bpf_map_update_elem(map_fd, &zero, &prog2_fd, BPF_ANY);
> +	}
> +
> +	return NULL;
> +}
> +
> +void test_tailcall_poke(void)
> +{
> +	struct tailcall_poke *call, *test;
> +	int err, cnt = 10;
> +	pthread_t thread;
> +
> +	unlink(JMP_TABLE);
> +
> +	call = tailcall_poke__open_and_load();
> +	if (!ASSERT_OK_PTR(call, "tailcall_poke__open"))
> +		return;
> +
> +	err = bpf_map__pin(call->maps.jmp_table, JMP_TABLE);
> +	if (!ASSERT_OK(err, "bpf_map__pin"))
> +		goto out;

Just curious. What is the reason having bpf_map__pin() here
and below? I tried and it looks like removing bpf_map__pin()
and below bpf_map__set_pin_path() will make reproducing
the failure hard/impossible.

> +
> +	err = pthread_create(&thread, NULL, update, call);
> +	if (!ASSERT_OK(err, "new toggler"))
> +		goto out;
> +
> +	while (cnt--) {
> +		test = tailcall_poke__open();
> +		if (!ASSERT_OK_PTR(test, "tailcall_poke__open"))
> +			break;
> +
> +		err = bpf_map__set_pin_path(test->maps.jmp_table, JMP_TABLE);
> +		if (!ASSERT_OK(err, "bpf_map__pin")) {
> +			tailcall_poke__destroy(test);
> +			break;
> +		}
> +
> +		bpf_program__set_autoload(test->progs.test, true);
> +		bpf_program__set_autoload(test->progs.call1, false);
> +		bpf_program__set_autoload(test->progs.call2, false);
> +
> +		err = tailcall_poke__load(test);
> +		tailcall_poke__destroy(test);
> +		if (!ASSERT_OK(err, "tailcall_poke__load"))
> +			break;
> +	}
> +
> +	thread_exit = 1;
> +	ASSERT_OK(pthread_join(thread, NULL), "pthread_join");
> +
> +out:
> +	bpf_map__unpin(call->maps.jmp_table, JMP_TABLE);
> +	tailcall_poke__destroy(call);
> +}
> diff --git a/tools/testing/selftests/bpf/progs/tailcall_poke.c b/tools/testing/selftests/bpf/progs/tailcall_poke.c
> new file mode 100644
> index 000000000000..c78b94b75e83
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/tailcall_poke.c
> @@ -0,0 +1,32 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <linux/bpf.h>
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +char _license[] SEC("license") = "GPL";
> +
> +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");
> +
> +SEC("?fentry/bpf_fentry_test1")
> +int BPF_PROG(test, int a)
> +{
> +	bpf_tail_call_static(ctx, &jmp_table, 0);
> +	return 0;
> +}
> +
> +SEC("fentry/bpf_fentry_test1")
> +int BPF_PROG(call1, int a)
> +{
> +	return 0;
> +}
> +
> +SEC("fentry/bpf_fentry_test1")
> +int BPF_PROG(call2, int a)
> +{
> +	return 0;
> +}