start_kernel() 연구 노트

initcall_debug
earlycon / keep_bootcon
ftrace=function_graph
trace_event=initcall:*,sched:*,irq:*
memblock=debug
rcupdate.rcu_cpu_stall_timeout=...

asmlinkage __visible __init __no_sanitize_address __noreturn __no_stack_protector
void start_kernel(void)
{
	char *command_line;
	char *after_dashes;

	set_task_stack_end_magic(&init_task);
	smp_setup_processor_id();
	debug_objects_early_init();
	init_vmlinux_build_id();

	cgroup_init_early();

	local_irq_disable();
	early_boot_irqs_disabled = true;

	/*
	 * Interrupts are still disabled. Do necessary setups, then
	 * enable them.
	 */
	boot_cpu_init();
	page_address_init();
	pr_notice("%s", linux_banner);
	early_security_init();
	setup_arch(&command_line);
	setup_boot_config();
	setup_command_line(command_line);
	setup_nr_cpu_ids();
	setup_per_cpu_areas();
	smp_prepare_boot_cpu();	/* arch-specific boot-cpu hooks */
	boot_cpu_hotplug_init();

	pr_notice("Kernel command line: %s\n", saved_command_line);
	/* parameters may set static keys */
	jump_label_init();
	parse_early_param();
	after_dashes = parse_args("Booting kernel",
				  static_command_line, __start___param,
				  __stop___param - __start___param,
				  -1, -1, NULL, &unknown_bootoption);
	print_unknown_bootoptions();
	if (!IS_ERR_OR_NULL(after_dashes))
		parse_args("Setting init args", after_dashes, NULL, 0, -1, -1,
			   NULL, set_init_arg);
	if (extra_init_args)
		parse_args("Setting extra init args", extra_init_args,
			   NULL, 0, -1, -1, NULL, set_init_arg);

	/* Architectural and non-timekeeping rng init, before allocator init */
	random_init_early(command_line);

	/*
	 * These use large bootmem allocations and must precede
	 * initalization of page allocator
	 */
	setup_log_buf(0);
	vfs_caches_init_early();
	sort_main_extable();
	trap_init();
	mm_core_init();
	poking_init();
	ftrace_init();

	/* trace_printk can be enabled here */
	early_trace_init();

	/*
	 * Set up the scheduler prior starting any interrupts (such as the
	 * timer interrupt). Full topology setup happens at smp_init()
	 * time - but meanwhile we still have a functioning scheduler.
	 */
	sched_init();

	radix_tree_init();
	maple_tree_init();

	housekeeping_init();
	workqueue_init_early();

	rcu_init();
	trace_init();

	if (initcall_debug)
		initcall_debug_enable();

	context_tracking_init();
	/* init some links before init_ISA_irqs() */
	early_irq_init();
	init_IRQ();
	tick_init();
	rcu_init_nohz();
	init_timers();
	srcu_init();
	hrtimers_init();
	softirq_init();
	timekeeping_init();
	time_init();

	random_init();
	kfence_init();
	boot_init_stack_canary();

	perf_event_init();
	profile_init();
	call_function_init();
	WARN(!irqs_disabled(), "Interrupts were enabled early\n");

	early_boot_irqs_disabled = false;
	local_irq_enable();

	kmem_cache_init_late();
	console_init();

	lockdep_init();
	locking_selftest();

	setup_per_cpu_pageset();
	numa_policy_init();
	acpi_early_init();
	if (late_time_init)
		late_time_init();
	sched_clock_init();
	calibrate_delay();

	arch_cpu_finalize_init();

	pid_idr_init();
	anon_vma_init();
	thread_stack_cache_init();
	cred_init();
	fork_init();
	proc_caches_init();
	uts_ns_init();
	key_init();
	security_init();
	dbg_late_init();
	net_ns_init();
	vfs_caches_init();
	pagecache_init();
	signals_init();
	seq_file_init();
	proc_root_init();
	nsfs_init();
	cpuset_init();
	cgroup_init();
	taskstats_init_early();
	delayacct_init();

	acpi_subsystem_init();
	arch_post_acpi_subsys_init();
	kcsan_init();

	/* Do the rest non-__init'ed, we're now alive */
	arch_call_rest_init();

noinline void __ref __noreturn rest_init(void)
{
	struct task_struct *tsk;
	int pid;

	rcu_scheduler_starting();
	pid = user_mode_thread(kernel_init, NULL, CLONE_FS);

	rcu_read_lock();
	tsk = find_task_by_pid_ns(pid, &init_pid_ns);
	tsk->flags |= PF_NO_SETAFFINITY;
	set_cpus_allowed_ptr(tsk, cpumask_of(smp_processor_id()));
	rcu_read_unlock();

	numa_default_policy();
	pid = kernel_thread(kthreadd, NULL, NULL, CLONE_FS | CLONE_FILES);
	rcu_read_lock();
	kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns);
	rcu_read_unlock();

	system_state = SYSTEM_SCHEDULING;
	complete(&kthreadd_done);

	schedule_preempt_disabled();
	cpu_startup_entry(CPUHP_ONLINE);
}

static void __init do_basic_setup(void)
{
	cpuset_init_smp();
	driver_init();
	init_irq_proc();
	do_ctors();
	do_initcalls();
}

wait_for_completion(&kthreadd_done);

kernel_init_freeable();
async_synchronize_full();

system_state = SYSTEM_FREEING_INITMEM;
kprobe_free_init_mem();
ftrace_free_init_mem();
kgdb_free_init_mem();
exit_boot_config();
free_initmem();
mark_readonly();
pti_finalize();

system_state = SYSTEM_RUNNING;
numa_default_policy();

rcu_end_inkernel_boot();

do_sysctl_args();

if (ramdisk_execute_command) {
	ret = run_init_process(ramdisk_execute_command);
	if (!ret)
		return 0;
	pr_err("Failed to execute %s (error %d)\n",
	       ramdisk_execute_command, ret);
}

if (execute_command) {
	ret = run_init_process(execute_command);
	if (!ret)
		return 0;
	panic("Requested init %s failed (error %d).",
	      execute_command, ret);
}

if (CONFIG_DEFAULT_INIT[0] != '\0') {
	ret = run_init_process(CONFIG_DEFAULT_INIT);
	if (ret)
		pr_err("Default init %s failed (error %d)\n",
		       CONFIG_DEFAULT_INIT, ret);
	else
		return 0;
}

if (!try_to_run_init_process("/sbin/init") ||
    !try_to_run_init_process("/etc/init") ||
    !try_to_run_init_process("/bin/init") ||
    !try_to_run_init_process("/bin/sh"))
	return 0;

panic("No working init found.  Try passing init= option to kernel. "
      "See Linux Documentation/admin-guide/init.rst for guidance.");