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From: Tianyi Chen <[email protected]> Date: Sun, 06 Sep 2026 22:34:48 +0800
The syscall test only prints the CPU selection result after checking whether BPF_PROG_TEST_RUN succeeds. Require -EBUSY for empty and affinity-disjoint custom masks, and allow a legal singleton candidate to be selected or busy. Reject unexpected errors and selections outside the custom mask or configured affinity. Check cpus_mask because migration disabling can temporarily narrow cpus_ptr under CONFIG_PREEMPT_RCU. Grow dynamically allocated affinity masks until sched_getaffinity() succeeds, retaining that allocation size for pinning and restoration. Restore affinity on all exits after pinning, and skip only the disjoint case when fewer than two CPUs are allowed. Assisted-by: LLM Signed-off-by: Tianyi Chen <[email protected]> --- Resending from my Gmail address because delivery from my previous address failed for the kernel.org and kernel mailing-list recipients. The patch is unchanged from v2 and still applies to sched_ext/for-7.4. Changes in v2: - Check configured affinity through p->cpus_mask, avoiding temporary cpus_ptr narrowing when migration is disabled. - Use zeroed, dynamically allocated affinity masks, retrying EINVAL with a larger size and handling restoration and cleanup on failure paths. - Rebase onto sched_ext/for-7.4. Validation: - Build and allowed_cpus tests passed with CONFIG_PREEMPT_RCU, including single-CPU affinity and ten runs under load with preempt=full. - A guest with 2048 possible CPUs and two online CPUs reproduced v1's EINVAL. V2 grew the mask from 128 to 256 bytes and passed with both full and single-CPU affinity. - Injected affinity-read, pinning, restoration and BPF test-run errors exercised failure handling, including restoration after a BPF failure. Forced mask growth with malloc perturbation also passed. v1: https://lore.kernel.org/r/[email protected] Review: https://lore.kernel.org/r/[email protected] .../selftests/sched_ext/allowed_cpus.bpf.c | 24 +++- .../selftests/sched_ext/allowed_cpus.c | 129 ++++++++++++++++-- 2 files changed, 135 insertions(+), 18 deletions(-) diff --git a/tools/testing/selftests/sched_ext/allowed_cpus.bpf.c b/tools/testing/selftests/sched_ext/allowed_cpus.bpf.c index 9dd72d0da29..f14d7e5bef9 100644 --- a/tools/testing/selftests/sched_ext/allowed_cpus.bpf.c +++ b/tools/testing/selftests/sched_ext/allowed_cpus.bpf.c @@ -147,23 +147,41 @@ void BPF_STRUCT_OPS(allowed_cpus_exit, struct scx_exit_info *ei) } struct task_cpu_arg { - pid_t pid; + u64 pid; + s64 custom_cpu; }; SEC("syscall") int select_cpu_from_user(struct task_cpu_arg *input) { struct task_struct *p; - int cpu; + struct bpf_cpumask *mask; + s32 cpu; p = bpf_task_from_pid(input->pid); if (!p) return -EINVAL; + mask = bpf_cpumask_create(); + if (!mask) { + bpf_task_release(p); + return -ENOMEM; + } + + /* A negative custom_cpu leaves the custom mask empty. */ + if (input->custom_cpu >= 0) + bpf_cpumask_set_cpu(input->custom_cpu, mask); + bpf_rcu_read_lock(); - cpu = scx_bpf_select_cpu_and(p, bpf_get_smp_processor_id(), 0, p->cpus_ptr, 0); + cpu = scx_bpf_select_cpu_and(p, bpf_get_smp_processor_id(), 0, + cast_mask(mask), 0); + if (cpu >= 0 && + (!bpf_cpumask_test_cpu(cpu, cast_mask(mask)) || + !bpf_cpumask_test_cpu(cpu, &p->cpus_mask))) + cpu = -ERANGE; bpf_rcu_read_unlock(); + bpf_cpumask_release(mask); bpf_task_release(p); return cpu; diff --git a/tools/testing/selftests/sched_ext/allowed_cpus.c b/tools/testing/selftests/sched_ext/allowed_cpus.c index 093f285ab4b..773699d120e 100644 --- a/tools/testing/selftests/sched_ext/allowed_cpus.c +++ b/tools/testing/selftests/sched_ext/allowed_cpus.c @@ -2,7 +2,10 @@ /* * Copyright (c) 2025 Andrea Righi <[email protected]> */ +#define _GNU_SOURCE #include <bpf/bpf.h> +#include <limits.h> +#include <sched.h> #include <scx/common.h> #include <sys/wait.h> #include <unistd.h> @@ -23,17 +26,19 @@ static enum scx_test_status setup(void **ctx) return SCX_TEST_PASS; } -static int test_select_cpu_from_user(const struct allowed_cpus *skel) +static int test_select_cpu_from_user(const struct allowed_cpus *skel, + const char *name, int custom_cpu, + bool expect_busy) { int fd, ret; - __u64 args[1]; + __s32 cpu; + __u64 args[] = { getpid(), (__u64)(__s64)custom_cpu }; LIBBPF_OPTS(bpf_test_run_opts, attr, .ctx_in = args, .ctx_size_in = sizeof(args), ); - args[0] = getpid(); fd = bpf_program__fd(skel->progs.select_cpu_from_user); if (fd < 0) return fd; @@ -42,29 +47,123 @@ static int test_select_cpu_from_user(const struct allowed_cpus *skel) if (ret < 0) return ret; - fprintf(stderr, "%s: CPU %d\n", __func__, attr.retval); + /* test_run returns the signed BPF result through an unsigned field. */ + cpu = (__s32)attr.retval; + if ((expect_busy && cpu != -EBUSY) || + (!expect_busy && cpu != -EBUSY && cpu != custom_cpu)) { + SCX_ERR("%s: unexpected CPU selection result %d", name, cpu); + return -EINVAL; + } return 0; } +/* Grow until the mask covers the kernel's CPU range, including offline CPUs. */ +static int alloc_affinity(cpu_set_t **mask, size_t *size) +{ + int nr_cpus = CPU_SETSIZE; + cpu_set_t *cpus; + int err; + + for (;;) { + *size = CPU_ALLOC_SIZE(nr_cpus); + cpus = CPU_ALLOC(nr_cpus); + if (!cpus) + return -ENOMEM; + CPU_ZERO_S(*size, cpus); + if (!sched_getaffinity(0, *size, cpus)) { + *mask = cpus; + return nr_cpus; + } + err = errno; + CPU_FREE(cpus); + if (err != EINVAL) + return -err; + if (nr_cpus > INT_MAX / 2) + return -EOVERFLOW; + nr_cpus *= 2; + } +} + static enum scx_test_status run(void *ctx) { struct allowed_cpus *skel = ctx; - struct bpf_link *link; + enum scx_test_status status = SCX_TEST_FAIL; + cpu_set_t *original = NULL, *pinned = NULL; + bool affinity_changed = false; + size_t size; + int first = -1, second = -1, cpu, nr_cpus; + struct bpf_link *link = NULL; + + nr_cpus = alloc_affinity(&original, &size); + if (nr_cpus < 0) { + SCX_ERR("Failed to get affinity (%d)", -nr_cpus); + goto out; + } + pinned = CPU_ALLOC(nr_cpus); + if (!pinned) { + SCX_ERR("Failed to allocate affinity mask"); + goto out; + } + for (cpu = 0; cpu < nr_cpus; cpu++) { + if (!CPU_ISSET_S(cpu, size, original)) + continue; + if (first < 0) { + first = cpu; + } else { + second = cpu; + break; + } + } + if (first < 0) { + SCX_ERR("No CPU in affinity mask"); + goto out; + } link = bpf_map__attach_struct_ops(skel->maps.allowed_cpus_ops); - SCX_FAIL_IF(!link, "Failed to attach scheduler"); - - /* Pick an idle CPU from user-space */ - SCX_FAIL_IF(test_select_cpu_from_user(skel), "Failed to pick idle CPU"); - - /* Just sleeping is fine, plenty of scheduling events happening */ + if (!link) { + SCX_ERR("Failed to attach scheduler"); + goto out; + } + + if (test_select_cpu_from_user(skel, "empty mask", -1, true)) + goto out; + + /* A legal candidate may be busy; selection need not succeed. */ + if (test_select_cpu_from_user(skel, "legal candidate", first, false)) + goto out; + + if (second >= 0) { + CPU_ZERO_S(size, pinned); + CPU_SET_S(first, size, pinned); + if (sched_setaffinity(0, size, pinned)) { + SCX_ERR("Failed to pin task (%d)", errno); + goto out; + } + affinity_changed = true; + if (test_select_cpu_from_user(skel, "disjoint masks", second, true)) + goto out; + } else { + fprintf(stderr, "Skipping disjoint masks: need two allowed CPUs\n"); + } + + /* Just sleeping is fine, plenty of scheduling events happening. */ sleep(1); - - SCX_EQ(skel->data->uei.kind, EXIT_KIND(SCX_EXIT_NONE)); + if (skel->data->uei.kind != EXIT_KIND(SCX_EXIT_NONE)) { + SCX_ERR("Scheduler exited unexpectedly"); + goto out; + } + status = SCX_TEST_PASS; + +out: + if (affinity_changed && sched_setaffinity(0, size, original)) { + SCX_ERR("Failed to restore affinity (%d)", errno); + status = SCX_TEST_FAIL; + } bpf_link__destroy(link); - - return SCX_TEST_PASS; + CPU_FREE(pinned); + CPU_FREE(original); + return status; } static void cleanup(void *ctx) -- 2.55.0
