For systems having CONFIG_NR_CPUS set to > 1024 in kernel config
the selftest fails as arena_spin_lock_irqsave() returns EOPNOTSUPP.
(eg - incase of powerpc default value for CONFIG_NR_CPUS is 8192)

The selftest is skipped incase bpf program returns EOPNOTSUPP,
with a descriptive message logged.

Tested-by: Venkat Rao Bagalkote <venka...@linux.ibm.com>
Signed-off-by: Saket Kumar Bhaskar <sk...@linux.ibm.com>
---

Changes since v2:
* Separated arena_spin_lock selftest fix patch from the arena
  patchset as it has to go via bpf-next tree.
* For EOPNOTSUPP set test_skip to 3, to differentiate it from
  scenarios when run conditions are not met as suggested by Hari.
* Tweaked message displayed on SKIP to remove display of online
  cpus.

v2:https://lore.kernel.org/all/20250829165135.1273071-1-sk...@linux.ibm.com/

Changes since v1:
Addressed comments from Alexei:
* Removed skel->rodata->nr_cpus = get_nprocs() and its usage to get
  currently online cpus(as it needs to be updated from userspace).

v1:https://lore.kernel.org/all/20250805062747.3479221-1-sk...@linux.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..693fd86fbde6 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 == 3) {
+               printf("%s:SKIP: CONFIG_NR_CPUS exceed the maximum supported by 
arena spinlock\n",
+                      __func__);
+               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..086b57a426cf 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 = 3;
                return ret;
+       }
        if (counter != limit)
                counter++;
        bpf_repeat(cs_count);
-- 
2.43.5


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