selftests/sched_ext: Update test enq_select_cpu_fails

With commit 08699d20467b6 ("sched_ext: idle: Consolidate default idle
CPU selection kfuncs") allowing scx_bpf_select_cpu_dfl() to be invoked
from multiple contexts, update the test to validate that the kfunc
behaves correctly when used from ops.enqueue() and via BPF test_run.

Additionally, rename the test to enq_select_cpu, dropping "fails" from
the name, as the logic has now been inverted.

Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

Author: arighi

tools/testing/selftests/sched_ext/Makefile

@@ -162,10 +162,10 @@ all_test_bpfprogs := $(foreach prog,$(wildcard *.bpf.c),$(INCLUDE_DIR)/$(patsubs
 auto-test-targets :=			\
 	create_dsq			\
 	enq_last_no_enq_fails		\
-	enq_select_cpu_fails		\
 	ddsp_bogus_dsq_fail		\
 	ddsp_vtimelocal_fail		\
 	dsp_local_on			\
+	enq_select_cpu			\
 	exit				\
 	hotplug				\
 	init_enable_count		\

tools/testing/selftests/sched_ext/enq_select_cpu.bpf.c

@@ -0,0 +1,74 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2023 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2023 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2023 Tejun Heo <tj@kernel.org>
+ */
+
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+UEI_DEFINE(uei);
+
+s32 BPF_STRUCT_OPS(enq_select_cpu_select_cpu, struct task_struct *p,
+		   s32 prev_cpu, u64 wake_flags)
+{
+	/* Bounce all tasks to ops.enqueue() */
+	return prev_cpu;
+}
+
+void BPF_STRUCT_OPS(enq_select_cpu_enqueue, struct task_struct *p,
+		    u64 enq_flags)
+{
+	s32 cpu, prev_cpu = scx_bpf_task_cpu(p);
+	bool found = false;
+
+	cpu = scx_bpf_select_cpu_dfl(p, prev_cpu, 0, &found);
+	if (found) {
+		scx_bpf_dsq_insert(p, SCX_DSQ_LOCAL_ON | cpu, SCX_SLICE_DFL, enq_flags);
+		return;
+	}
+
+	scx_bpf_dsq_insert(p, SCX_DSQ_GLOBAL, SCX_SLICE_DFL, enq_flags);
+}
+
+void BPF_STRUCT_OPS(enq_select_cpu_exit, struct scx_exit_info *ei)
+{
+	UEI_RECORD(uei, ei);
+}
+
+struct task_cpu_arg {
+	pid_t pid;
+};
+
+SEC("syscall")
+int select_cpu_from_user(struct task_cpu_arg *input)
+{
+	struct task_struct *p;
+	bool found = false;
+	s32 cpu;
+
+	p = bpf_task_from_pid(input->pid);
+	if (!p)
+		return -EINVAL;
+
+	bpf_rcu_read_lock();
+	cpu = scx_bpf_select_cpu_dfl(p, bpf_get_smp_processor_id(), 0, &found);
+	if (!found)
+		cpu = -EBUSY;
+	bpf_rcu_read_unlock();
+
+	bpf_task_release(p);
+
+	return cpu;
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops enq_select_cpu_ops = {
+	.select_cpu		= (void *)enq_select_cpu_select_cpu,
+	.enqueue		= (void *)enq_select_cpu_enqueue,
+	.exit			= (void *)enq_select_cpu_exit,
+	.name			= "enq_select_cpu",
+	.timeout_ms		= 1000U,
+};

tools/testing/selftests/sched_ext/enq_select_cpu.c

@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2023 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2023 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2023 Tejun Heo <tj@kernel.org>
+ */
+#include <bpf/bpf.h>
+#include <scx/common.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include "enq_select_cpu.bpf.skel.h"
+#include "scx_test.h"
+
+static enum scx_test_status setup(void **ctx)
+{
+	struct enq_select_cpu *skel;
+
+	skel = enq_select_cpu__open();
+	SCX_FAIL_IF(!skel, "Failed to open");
+	SCX_ENUM_INIT(skel);
+	SCX_FAIL_IF(enq_select_cpu__load(skel), "Failed to load skel");
+
+	*ctx = skel;
+
+	return SCX_TEST_PASS;
+}
+
+static int test_select_cpu_from_user(const struct enq_select_cpu *skel)
+{
+	int fd, ret;
+	__u64 args[1];
+
+	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;
+
+	ret = bpf_prog_test_run_opts(fd, &attr);
+	if (ret < 0)
+		return ret;
+
+	fprintf(stderr, "%s: CPU %d\n", __func__, attr.retval);
+
+	return 0;
+}
+
+static enum scx_test_status run(void *ctx)
+{
+	struct enq_select_cpu *skel = ctx;
+	struct bpf_link *link;
+
+	link = bpf_map__attach_struct_ops(skel->maps.enq_select_cpu_ops);
+	if (!link) {
+		SCX_ERR("Failed to attach scheduler");
+		return SCX_TEST_FAIL;
+	}
+
+	/* Pick an idle CPU from user-space */
+	SCX_FAIL_IF(test_select_cpu_from_user(skel), "Failed to pick idle CPU");
+
+	sleep(1);
+
+	SCX_EQ(skel->data->uei.kind, EXIT_KIND(SCX_EXIT_NONE));
+	bpf_link__destroy(link);
+
+	return SCX_TEST_PASS;
+}
+
+static void cleanup(void *ctx)
+{
+	struct enq_select_cpu *skel = ctx;
+
+	enq_select_cpu__destroy(skel);
+}
+
+struct scx_test enq_select_cpu = {
+	.name = "enq_select_cpu",
+	.description = "Verify scx_bpf_select_cpu_dfl() from multiple contexts",
+	.setup = setup,
+	.run = run,
+	.cleanup = cleanup,
+};
+REGISTER_SCX_TEST(&enq_select_cpu)