linux-kernel - Re: [PATCH 2/2] perf tests sigtrap: Skip if running on a kernel with sleepable spinlocks

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Date:   Thu, 30 Nov 2023 14:28:33 +0100
From:   Marco Elver <elver@...gle.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Namhyung Kim <namhyung@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Clark Williams <williams@...hat.com>,
        Kate Carcia <kcarcia@...hat.com>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Mike Galbraith <efault@....de>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 2/2] perf tests sigtrap: Skip if running on a kernel with
 sleepable spinlocks

On Thu, 30 Nov 2023 at 14:01, Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
>
> Em Wed, Nov 29, 2023 at 05:42:30PM -0300, Arnaldo Carvalho de Melo escreveu:
> > Em Wed, Nov 29, 2023 at 04:57:47PM +0100, Marco Elver escreveu:
> > > > @@ -175,7 +208,16 @@ static int run_stress_test(int fd, pthread_t *threads, pthread_barrier_t *barrie
> > > >         ret = run_test_threads(threads, barrier);
> > > >         TEST_ASSERT_EQUAL("disable failed", ioctl(fd, PERF_EVENT_IOC_DISABLE, 0), 0);
>
> > > > -       TEST_ASSERT_EQUAL("unexpected sigtraps", ctx.signal_count, NUM_THREADS * ctx.iterate_on);
> > > > +       expected_sigtraps = NUM_THREADS * ctx.iterate_on;
>
> > > > +       if (ctx.signal_count < expected_sigtraps && kernel_with_sleepable_spinlocks()) {
> > > > +               pr_debug("Expected %d sigtraps, got %d, running on a kernel with sleepable spinlocks.\n",
> > > > +                        expected_sigtraps, ctx.signal_count);
> > > > +               pr_debug("See https://lore.kernel.org/all/e368f2c848d77fbc8d259f44e2055fe469c219cf.camel@gmx.de/\n");
>
> > > No changes from the RT side since? A fix exists, but apparently not
> > > good enough... Sigh.
>
> > Yeah, my impression, and first attempt at writing that patch wast that
> > no sigtraps were being sent, but then when I tried with a random, more
> > recent machine in the Red Hat labs, I got some signals, way less than
> > the expected ones, but some, maybe this is an interesting data point?
>
> > I'll try again to reproduce in the local machine, old i7 lenovo notebook
> > and at the newer machine, a Xeon(R) Silver 4216, 32 cpu and report here.
>
> So, on the i7 lenovo:
>
> [root@...e ~]# uname -a
> Linux nine 5.14.0-284.30.1.rt14.315.el9_2.x86_64 #1 SMP PREEMPT_RT Fri Aug 25 10:53:59 EDT 2023 x86_64 x86_64 x86_64 GNU/Linux
[...]
>
> I guess I'll try to get hold of the older kernel with 0 sigtraps to see
> if I get the same behaviour (consistent 0 sigtraps) on that kernel on
> the bigger machine :-\

Thanks for checking.

In any case, it looks like it's still broken. If the fix (bf9ad37dc8a
+ small diff by Mike) from [1] still works, what's blocking it from
being upstreamed?

https://lore.kernel.org/all/e368f2c848d77fbc8d259f44e2055fe469c219cf.camel@gmx.de/