进程fork处理

进程或者线程创建do_fork

/* For compatibility with architectures that call do_fork directly rather than
 * using the syscall entry points below. */
long do_fork(unsigned long clone_flags,
       unsigned long stack_start,
       unsigned long stack_size,
       int __user *parent_tidptr,
       int __user *child_tidptr)
{
 return _do_fork(clone_flags, stack_start, stack_size,
   parent_tidptr, child_tidptr, 0);
}
 

/*
 *  Ok, this is the main fork-routine.
 *
 * It copies the process, and if successful kick-starts
 * it and waits for it to finish using the VM if required.
 */
long _do_fork(unsigned long clone_flags,
       unsigned long stack_start,
       unsigned long stack_size,
       int __user *parent_tidptr,
       int __user *child_tidptr,
       unsigned long tls)
{
 struct task_struct *p;
 int trace = 0;
 long nr;
 /*
  * Determine whether and which event to report to ptracer.  When
  * called from kernel_thread or CLONE_UNTRACED is explicitly
  * requested, no event is reported; otherwise, report if the event
  * for the type of forking is enabled.
  */
 if (!(clone_flags & CLONE_UNTRACED)) {
  if (clone_flags & CLONE_VFORK)
   trace = PTRACE_EVENT_VFORK;
  else if ((clone_flags & CSIGNAL) != SIGCHLD)
   trace = PTRACE_EVENT_CLONE;
  else
   trace = PTRACE_EVENT_FORK;
  if (likely(!ptrace_event_enabled(current, trace)))
   trace = 0;
 }
 p = copy_process(clone_flags, stack_start, stack_size,
    child_tidptr, NULL, trace, tls, NUMA_NO_NODE);
 add_latent_entropy();
 /*
  * Do this prior waking up the new thread - the thread pointer
  * might get invalid after that point, if the thread exits quickly.
  */
 if (!IS_ERR(p)) {
  struct completion vfork;
  struct pid *pid;
  trace_sched_process_fork(current, p);
  pid = get_task_pid(p, PIDTYPE_PID);
  nr = pid_vnr(pid);
  if (clone_flags & CLONE_PARENT_SETTID)
   put_user(nr, parent_tidptr);
  if (clone_flags & CLONE_VFORK) {
   p->vfork_done = &vfork;
   init_completion(&vfork);
   get_task_struct(p);
  }
  wake_up_new_task(p);
  /* forking complete and child started to run, tell ptracer */
  if (unlikely(trace))
   ptrace_event_pid(trace, pid);
  if (clone_flags & CLONE_VFORK) {
   if (!wait_for_vfork_done(p, &vfork))
    ptrace_event_pid(PTRACE_EVENT_VFORK_DONE, pid);
  }
  put_pid(pid);
 } else {
  nr = PTR_ERR(p);
 }
 return nr;
}