Message-ID: <CAEf4Bza3cd5cMRvouUiVNrt5MRU4Nhpo7i0KEy1Gm5DTgOFszw@mail.gmail.com>
Date: Thu, 15 May 2025 10:31:28 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Jiri Olsa <jolsa@...nel.org>
Cc: Oleg Nesterov <oleg@...hat.com>, Peter Zijlstra <peterz@...radead.org>, 
	Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-trace-kernel@...r.kernel.org, x86@...nel.org, 
	Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>, 
	John Fastabend <john.fastabend@...il.com>, Hao Luo <haoluo@...gle.com>, 
	Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>, 
	Alan Maguire <alan.maguire@...cle.com>, David Laight <David.Laight@...lab.com>, 
	Thomas Weißschuh <thomas@...ch.de>, 
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCHv2 perf/core 15/22] selftests/bpf: Add hit/attach/detach
 race optimized uprobe test

On Thu, May 15, 2025 at 5:15 AM Jiri Olsa <jolsa@...nel.org> wrote:
>
> Adding test that makes sure parallel execution of the uprobe and
> attach/detach of optimized uprobe on it works properly.
>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  .../selftests/bpf/prog_tests/uprobe_syscall.c | 94 +++++++++++++++++++
>  1 file changed, 94 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c b/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
> index b9152ca8cdf5..a83abbe91b01 100644
> --- a/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
> +++ b/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
> @@ -15,6 +15,7 @@
>  #include <asm/prctl.h>
>  #include "uprobe_syscall.skel.h"
>  #include "uprobe_syscall_executed.skel.h"
> +#include "bpf/libbpf_internal.h"
>
>  #define USDT_NOP .byte 0x0f, 0x1f, 0x44, 0x00, 0x00
>  #include "usdt.h"
> @@ -634,6 +635,97 @@ static void test_uretprobe_shadow_stack(void)
>         ARCH_PRCTL(ARCH_SHSTK_DISABLE, ARCH_SHSTK_SHSTK);
>  }
>
> +static volatile bool race_stop;
> +
> +static USDT_DEFINE_SEMA(race);
> +
> +static void *worker_trigger(void *arg)
> +{
> +       unsigned long rounds = 0;
> +
> +       while (!race_stop) {
> +               uprobe_test();
> +               rounds++;
> +       }
> +
> +       printf("tid %d trigger rounds: %lu\n", gettid(), rounds);
> +       return NULL;
> +}
> +
> +static void *worker_attach(void *arg)
> +{
> +       LIBBPF_OPTS(bpf_uprobe_opts, opts);
> +       struct uprobe_syscall_executed *skel;
> +       unsigned long rounds = 0, offset;
> +       const char *sema[2] = {
> +               __stringify(USDT_SEMA(race)),
> +               NULL,
> +       };
> +       unsigned long *ref;
> +       int err;
> +
> +       offset = get_uprobe_offset(&uprobe_test);
> +       if (!ASSERT_GE(offset, 0, "get_uprobe_offset"))
> +               return NULL;
> +
> +       err = elf_resolve_syms_offsets("/proc/self/exe", 1, (const char **) &sema, &ref, STT_OBJECT);
> +       if (!ASSERT_OK(err, "elf_resolve_syms_offsets_sema"))
> +               return NULL;
> +
> +       opts.ref_ctr_offset = *ref;
> +
> +       skel = uprobe_syscall_executed__open_and_load();
> +       if (!ASSERT_OK_PTR(skel, "uprobe_syscall_executed__open_and_load"))
> +               return NULL;
> +
> +       while (!race_stop) {
> +               skel->links.test_uprobe = bpf_program__attach_uprobe_opts(skel->progs.test_uprobe,
> +                                       0, "/proc/self/exe", offset, &opts);
> +               if (!ASSERT_OK_PTR(skel->links.test_uprobe, "bpf_program__attach_uprobe_opts"))
> +                       break;
> +
> +               bpf_link__destroy(skel->links.test_uprobe);
> +               skel->links.test_uprobe = NULL;
> +               rounds++;
> +       }
> +
> +       printf("tid %d attach rounds: %lu hits: %d\n", gettid(), rounds, skel->bss->executed);
> +       uprobe_syscall_executed__destroy(skel);
> +       free(ref);
> +       return NULL;
> +}
> +
> +static void test_uprobe_race(void)
> +{
> +       int err, i, nr_threads;
> +       pthread_t *threads;
> +
> +       nr_threads = libbpf_num_possible_cpus();
> +       if (!ASSERT_GT(nr_threads, 0, "libbpf_num_possible_cpus"))
> +               return;
> +       nr_threads = max(2, nr_threads);
> +
> +       threads = malloc(sizeof(*threads) * nr_threads);

leaking this? maybe just use `pthread_t thread[nr_threads];`? or alloca()?

> +       if (!ASSERT_OK_PTR(threads, "malloc"))
> +               return;
> +
> +       for (i = 0; i < nr_threads; i++) {
> +               err = pthread_create(&threads[i], NULL, i % 2 ? worker_trigger : worker_attach,
> +                                    NULL);
> +               if (!ASSERT_OK(err, "pthread_create"))
> +                       goto cleanup;
> +       }
> +
> +       sleep(4);

4 seconds... can we make it much shorter and allow to define the
actual runtime with envvar? So for thorough testing you'll define
something multi-second, but once things land and settle we can run it
for 100ms at most and not slow down CI significantly? All these slow
tests do add up :(

> +
> +cleanup:
> +       race_stop = true;
> +       for (nr_threads = i, i = 0; i < nr_threads; i++)
> +               pthread_join(threads[i], NULL);
> +
> +       ASSERT_FALSE(USDT_SEMA_IS_ACTIVE(race), "race_semaphore");
> +}
> +
>  static void __test_uprobe_syscall(void)
>  {
>         if (test__start_subtest("uretprobe_regs_equal"))
> @@ -652,6 +744,8 @@ static void __test_uprobe_syscall(void)
>                 test_uprobe_session();
>         if (test__start_subtest("uprobe_usdt"))
>                 test_uprobe_usdt();
> +       if (test__start_subtest("uprobe_race"))
> +               test_uprobe_race();
>  }
>  #else
>  static void __test_uprobe_syscall(void)
> --
> 2.49.0
>

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