The test_populate test uses >= instead of > when checking if the runtime nr_cpus exceeds the bit capacity of a cpumask_t. On a system where the physical CPU core count perfectly matches the CONFIG_NR_CPUS upper bound (e.g. nr_cpus = 512 and CONFIG_NR_CPUS = 512), the condition nr_cpus >= CPUMASK_TEST_MASKLEN * 8 evaluates to true (512 >= 512). This incorrectly causes the test to fail with an error value of 3. A 512-bit cpumask_t provides enough bits (indices 0 through 511) to represent 512 CPUs. The subsequent bpf_for(i, 0, nr_cpus) loop iterates up to nr_cpus - 1 (511), which perfectly aligns with the maximum valid index of the bitmask. Change the condition to nr_cpus > CPUMASK_TEST_MASKLEN * 8 to fix the false positive failure on these systems. Fixes: 918ba2636d4e ("selftests: bpf: add bpf_cpumask_populate selftests") Signed-off-by: Matt Bobrowski --- tools/testing/selftests/bpf/progs/cpumask_success.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/tools/testing/selftests/bpf/progs/cpumask_success.c b/tools/testing/selftests/bpf/progs/cpumask_success.c index 0e04c31b91c0..774706e7b058 100644 --- a/tools/testing/selftests/bpf/progs/cpumask_success.c +++ b/tools/testing/selftests/bpf/progs/cpumask_success.c @@ -866,7 +866,7 @@ int BPF_PROG(test_populate, struct task_struct *task, u64 clone_flags) * access NR_CPUS, the upper bound for nr_cpus, so we infer * it from the size of cpumask_t. */ - if (nr_cpus < 0 || nr_cpus >= CPUMASK_TEST_MASKLEN * 8) { + if (nr_cpus < 0 || nr_cpus > CPUMASK_TEST_MASKLEN * 8) { err = 3; goto out; } -- 2.54.0.rc1.513.gad8abe7a5a-goog