版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/rikeyone/article/details/84029241
idle进程是内核创建的第一个进程，也常常被叫做swapper 进程:
asmlinkage __visible void __init start_kernel(void)
{
char *command_line;
char *after_dashes;
set_task_stack_end_magic(&init_task);
idle进程也是唯一一个不是通过fork产生的进程，他是静态定义的一个进程，init_task就是它的任务结构体。在start_kernel函数的最后：
asmlinkage __visible void __init start_kernel(void)
{
......
/* Do the rest non-__init'ed, we're now alive */
rest_init();
}
rest_init函数中会创建我们系统的第一个用户空间进程，那就是大名鼎鼎的pid为1的init进程。init进程是所有用户空间进程的祖先进程，而idle进程是所有进程的祖先进程。
static noinline void __ref rest_init(void)
{
struct task_struct *tsk;
int pid;
rcu_scheduler_starting();
/*
* We need to spawn init first so that it obtains pid 1, however
* the init task will end up wanting to create kthreads, which, if
* we schedule it before we create kthreadd, will OOPS.
*/
pid = kernel_thread(kernel_init, NULL, CLONE_FS);
static int __ref kernel_init(void *unused)
{
int ret;
kernel_init_freeable();
/* need to finish all async __init code before freeing the memory */
async_synchronize_full();
ftrace_free_init_mem();
free_initmem();
mark_readonly();
system_state = SYSTEM_RUNNING;
numa_default_policy();
rcu_end_inkernel_boot();
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);
}
/*
* We try each of these until one succeeds.
*
* The Bourne shell can be used instead of init if we are
* trying to recover a really broken machine.
*/
if (execute_command) {
ret = run_init_process(execute_command);
if (!ret)
return 0;
panic("Requested init %s failed (error %d).",
execute_command, ret);
}
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. "
在init进程创建完成后，该进程还会创建kthreadd进程，最后进入do_idle，也就是我们所说的idle进程所做的事情，让cpu 进入idle状态。
void cpu_startup_entry(enum cpuhp_state state)
{
/*
* This #ifdef needs to die, but it's too late in the cycle to
* make this generic (arm and sh have never invoked the canary
* init for the non boot cpus!). Will be fixed in 3.11
*/
#ifdef CONFIG_X86
/*
* If we're the non-boot CPU, nothing set the stack canary up
* for us. The boot CPU already has it initialized but no harm
* in doing it again. This is a good place for updating it, as
* we wont ever return from this function (so the invalid
* canaries already on the stack wont ever trigger).
*/
boot_init_stack_canary();
#endif
arch_cpu_idle_prepare();
cpuhp_online_idle(state);
while (1)
do_idle();
}