linux-kernel - Re: [PATCH perf/core 15/22] selftests/bpf: Add hit/attach/detach race optimized uprobe test

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Message-ID: <CAEf4BzbLhc1PO=AfuavYhy+68Rj3u6d4OWpzZcExcOpdqMFMdA@mail.gmail.com>
Date: Thu, 24 Apr 2025 09:30:21 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Jiri Olsa <olsajiri@...il.com>
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: [PATCH perf/core 15/22] selftests/bpf: Add hit/attach/detach race
 optimized uprobe test

On Thu, Apr 24, 2025 at 5:51 AM Jiri Olsa <olsajiri@...il.com> wrote:
>
> On Wed, Apr 23, 2025 at 10:42:43AM -0700, Andrii Nakryiko wrote:
>
> SNIP
>
> > > +
> > > +static void test_uprobe_race(void)
> > > +{
> > > +       int err, i, nr_threads;
> > > +       pthread_t *threads;
> > > +
> > > +       nr_threads = libbpf_num_possible_cpus();
> > > +       if (!ASSERT_GE(nr_threads, 0, "libbpf_num_possible_cpus"))
> >
> > I hope there are strictly more than zero CPUs... ;)
> >
> > > +               return;
> > > +
> > > +       threads = malloc(sizeof(*threads) * nr_threads);
> > > +       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);
> >
> > What happens when three is just one CPU?
> >
>
> right, we need at least 2 threads, how about the change below
>
> thanks,
> jirka
>
>
> ---
> diff --git a/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c b/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
> index d55c3579cebe..c885f097eed4 100644
> --- a/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
> +++ b/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
> @@ -701,8 +701,9 @@ static void test_uprobe_race(void)
>         pthread_t *threads;
>
>         nr_threads = libbpf_num_possible_cpus();
> -       if (!ASSERT_GE(nr_threads, 0, "libbpf_num_possible_cpus"))
> +       if (!ASSERT_GT(nr_threads, 0, "libbpf_num_possible_cpus"))
>                 return;
> +       nr_threads = max(2, nr_threads);

yep, ack

>
>         threads = malloc(sizeof(*threads) * nr_threads);
>         if (!ASSERT_OK_PTR(threads, "malloc"))