linux-kernel - Re: [PATCH bpf-next v2 5/5] selftests/bpf: Fix arena_spin

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Message-ID: <aLlNBK9Zm+N4zarF@linux.ibm.com>
Date: Thu, 4 Sep 2025 13:55:40 +0530
From: Saket Kumar Bhaskar <skb99@...ux.ibm.com>
To: Hari Bathini <hbathini@...ux.ibm.com>
Cc: bpf@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        sachinpb@...ux.ibm.com, venkat88@...ux.ibm.com, andrii@...nel.org,
        eddyz87@...il.com, mykolal@...com, ast@...nel.org,
        daniel@...earbox.net, martin.lau@...ux.dev, song@...nel.org,
        yonghong.song@...ux.dev, john.fastabend@...il.com, kpsingh@...nel.org,
        sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org,
        christophe.leroy@...roup.eu, naveen@...nel.org, maddy@...ux.ibm.com,
        mpe@...erman.id.au, npiggin@...il.com, memxor@...il.com,
        iii@...ux.ibm.com, shuah@...nel.org
Subject: Re: [PATCH bpf-next v2 5/5] selftests/bpf: Fix arena_spin_lock
 selftest failure

On Thu, Sep 04, 2025 at 01:39:31PM +0530, Hari Bathini wrote:
> 
> 
> On 29/08/25 10:21 pm, Saket Kumar Bhaskar wrote:
> > For systems having CONFIG_NR_CPUS set to > 1024 in kernel config
> > the selftest fails as arena_spin_lock_irqsave() returns EOPNOTSUPP.
> > 
> > The selftest is skipped incase bpf program returns EOPNOTSUPP,
> > with a descriptive message logged.
> > 
> > Signed-off-by: Saket Kumar Bhaskar <skb99@...ux.ibm.com>
> > ---
> >   .../selftests/bpf/prog_tests/arena_spin_lock.c      | 13 +++++++++++++
> >   tools/testing/selftests/bpf/progs/arena_spin_lock.c |  5 ++++-
> >   2 files changed, 17 insertions(+), 1 deletion(-)
> > 
> > diff --git a/tools/testing/selftests/bpf/prog_tests/arena_spin_lock.c b/tools/testing/selftests/bpf/prog_tests/arena_spin_lock.c
> > index 0223fce4db2b..1ec1ca987893 100644
> > --- a/tools/testing/selftests/bpf/prog_tests/arena_spin_lock.c
> > +++ b/tools/testing/selftests/bpf/prog_tests/arena_spin_lock.c
> > @@ -40,8 +40,13 @@ static void *spin_lock_thread(void *arg)
> >   	err = bpf_prog_test_run_opts(prog_fd, &topts);
> >   	ASSERT_OK(err, "test_run err");
> > +
> > +	if (topts.retval == -EOPNOTSUPP)
> > +		goto end;
> > +
> >   	ASSERT_EQ((int)topts.retval, 0, "test_run retval");
> > +end:
> >   	pthread_exit(arg);
> >   }
> > @@ -63,6 +68,7 @@ static void test_arena_spin_lock_size(int size)
> >   	skel = arena_spin_lock__open_and_load();
> >   	if (!ASSERT_OK_PTR(skel, "arena_spin_lock__open_and_load"))
> >   		return;
> > +
> >   	if (skel->data->test_skip == 2) {
> >   		test__skip();
> >   		goto end;
> > @@ -86,6 +92,13 @@ static void test_arena_spin_lock_size(int size)
> >   			goto end_barrier;
> >   	}
> > +	if (skel->data->test_skip == 2) {
> > +		printf("%s:SKIP: %d CPUs exceed the maximum supported by arena spinlock\n",
> > +		       __func__, get_nprocs());
> > +		test__skip();
> > +		goto end_barrier;
> > +	}
> > +
> >   	ASSERT_EQ(skel->bss->counter, repeat * nthreads, "check counter value");
> >   end_barrier:
> > diff --git a/tools/testing/selftests/bpf/progs/arena_spin_lock.c b/tools/testing/selftests/bpf/progs/arena_spin_lock.c
> > index c4500c37f85e..a475b974438e 100644
> > --- a/tools/testing/selftests/bpf/progs/arena_spin_lock.c
> > +++ b/tools/testing/selftests/bpf/progs/arena_spin_lock.c
> > @@ -37,8 +37,11 @@ int prog(void *ctx)
> >   #if defined(ENABLE_ATOMICS_TESTS) && defined(__BPF_FEATURE_ADDR_SPACE_CAST)
> >   	unsigned long flags;
> > -	if ((ret = arena_spin_lock_irqsave(&lock, flags)))
> > +	if ((ret = arena_spin_lock_irqsave(&lock, flags))) {
> > +		if (ret == -EOPNOTSUPP)
> > +			test_skip = 2;
> >   		return ret;
> 
> test_skip being set to `1` when the test runs seems counter intuitive.
> How about setting test_skip to `0` when run conditions are met
> and test_skip=1 if run conditions are not met and
> test_skip=2 when operation is not supported?
> 
> - Hari
That seems reasonable to me, but right now -EOPNOTSUPP is also
returned when run condition is not met i.e.:

  if (CONFIG_NR_CPUS > 1024)
                return -EOPNOTSUPP;

So do we really need test_skip = 2 ?

Thanks,
Saket