/*
   *  linux/kernel/exit.c
   *
   *  Copyright (C) 1991, 1992  Linus Torvalds
   */

  #include <linux/mm.h>
  #include <linux/slab.h>
  #include <linux/interrupt.h>

  #include <linux/module.h>

  #include <linux/capability.h>

  #include <linux/completion.h>
  #include <linux/personality.h>
  #include <linux/tty.h>

  #include <linux/iocontext.h>

  #include <linux/key.h>
  #include <linux/security.h>
  #include <linux/cpu.h>
  #include <linux/acct.h>

  #include <linux/tsacct_kern.h>

  #include <linux/file.h>

  #include <linux/fdtable.h>

  #include <linux/binfmts.h>

  #include <linux/nsproxy.h>

  #include <linux/pid_namespace.h>

  #include <linux/ptrace.h>
  #include <linux/profile.h>
  #include <linux/mount.h>
  #include <linux/proc_fs.h>

  #include <linux/kthread.h>

  #include <linux/mempolicy.h>

  #include <linux/taskstats_kern.h>

  #include <linux/delayacct.h>

  #include <linux/freezer.h>

  #include <linux/cgroup.h>

  #include <linux/syscalls.h>

  #include <linux/signal.h>

  #include <linux/posix-timers.h>

  #include <linux/cn_proc.h>

  #include <linux/mutex.h>

  #include <linux/futex.h>

  #include <linux/pipe_fs_i.h>

  #include <linux/audit.h> /* for audit_free() */

  #include <linux/resource.h>

  #include <linux/blkdev.h>

  #include <linux/task_io_accounting_ops.h>

  #include <linux/tracehook.h>

  #include <linux/fs_struct.h>

  #include <linux/init_task.h>

  #include <linux/perf_event.h>

  #include <trace/events/sched.h>

  #include <linux/hw_breakpoint.h>

  #include <linux/oom.h>

  
  #include <asm/uaccess.h>
  #include <asm/unistd.h>
  #include <asm/pgtable.h>
  #include <asm/mmu_context.h>

  static void exit_mm(struct task_struct * tsk);

  static void __unhash_process(struct task_struct *p, bool group_dead)

  {
  	nr_threads--;
  	detach_pid(p, PIDTYPE_PID);

  	if (group_dead) {

  		detach_pid(p, PIDTYPE_PGID);
  		detach_pid(p, PIDTYPE_SID);

  		list_del_rcu(&p->tasks);

  		list_del_init(&p->sibling);

  		__this_cpu_dec(process_counts);

  	}

  	list_del_rcu(&p->thread_group);

  }

  /*
   * This function expects the tasklist_lock write-locked.
   */
  static void __exit_signal(struct task_struct *tsk)
  {
  	struct signal_struct *sig = tsk->signal;

  	bool group_dead = thread_group_leader(tsk);

  	struct sighand_struct *sighand;

  	struct tty_struct *uninitialized_var(tty);

  	sighand = rcu_dereference_check(tsk->sighand,
  					rcu_read_lock_held() ||

  					lockdep_tasklist_lock_is_held());

  	spin_lock(&sighand->siglock);
  
  	posix_cpu_timers_exit(tsk);

  	if (group_dead) {

  		posix_cpu_timers_exit_group(tsk);

  		tty = sig->tty;
  		sig->tty = NULL;

  	} else {

  		/*

  		 * This can only happen if the caller is de_thread().
  		 * FIXME: this is the temporary hack, we should teach
  		 * posix-cpu-timers to handle this case correctly.
  		 */
  		if (unlikely(has_group_leader_pid(tsk)))
  			posix_cpu_timers_exit_group(tsk);
  
  		/*

  		 * If there is any task waiting for the group exit
  		 * then notify it:
  		 */

  		if (sig->notify_count > 0 && !--sig->notify_count)

  			wake_up_process(sig->group_exit_task);

  		if (tsk == sig->curr_target)
  			sig->curr_target = next_thread(tsk);
  		/*
  		 * Accumulate here the counters for all threads but the
  		 * group leader as they die, so they can be added into
  		 * the process-wide totals when those are taken.
  		 * The group leader stays around as a zombie as long
  		 * as there are other threads.  When it gets reaped,
  		 * the exit.c code will add its counts into these totals.
  		 * We won't ever get here for the group leader, since it
  		 * will have been the last reference on the signal_struct.
  		 */

  		sig->utime = cputime_add(sig->utime, tsk->utime);
  		sig->stime = cputime_add(sig->stime, tsk->stime);

  		sig->gtime = cputime_add(sig->gtime, tsk->gtime);

  		sig->min_flt += tsk->min_flt;
  		sig->maj_flt += tsk->maj_flt;
  		sig->nvcsw += tsk->nvcsw;
  		sig->nivcsw += tsk->nivcsw;

  		sig->inblock += task_io_get_inblock(tsk);
  		sig->oublock += task_io_get_oublock(tsk);

  		task_io_accounting_add(&sig->ioac, &tsk->ioac);

  		sig->sum_sched_runtime += tsk->se.sum_exec_runtime;

  	}

  	sig->nr_threads--;

  	__unhash_process(tsk, group_dead);

  	/*
  	 * Do this under ->siglock, we can race with another thread
  	 * doing sigqueue_free() if we have SIGQUEUE_PREALLOC signals.
  	 */
  	flush_sigqueue(&tsk->pending);

  	tsk->sighand = NULL;

  	spin_unlock(&sighand->siglock);

  	__cleanup_sighand(sighand);

  	clear_tsk_thread_flag(tsk,TIF_SIGPENDING);

  	if (group_dead) {

  		flush_sigqueue(&sig->shared_pending);

  		tty_kref_put(tty);

  	}
  }

  static void delayed_put_task_struct(struct rcu_head *rhp)
  {

  	struct task_struct *tsk = container_of(rhp, struct task_struct, rcu);

  	perf_event_delayed_put(tsk);

  	trace_sched_process_free(tsk);
  	put_task_struct(tsk);

  }

  void release_task(struct task_struct * p)
  {

  	struct task_struct *leader;

  	int zap_leader;

  repeat:

  	tracehook_prepare_release_task(p);

  	/* don't need to get the RCU readlock here - the process is dead and

  	 * can't be modifying its own credentials. But shut RCU-lockdep up */
  	rcu_read_lock();

  	atomic_dec(&__task_cred(p)->user->processes);

  	rcu_read_unlock();

  	proc_flush_task(p);

  	write_lock_irq(&tasklist_lock);

  	tracehook_finish_release_task(p);

  	__exit_signal(p);

  	/*
  	 * If we are the last non-leader member of the thread
  	 * group, and the leader is zombie, then notify the
  	 * group leader's parent process. (if it wants notification.)
  	 */
  	zap_leader = 0;
  	leader = p->group_leader;
  	if (leader != p && thread_group_empty(leader) && leader->exit_state == EXIT_ZOMBIE) {

  		BUG_ON(task_detached(leader));

  		do_notify_parent(leader, leader->exit_signal);
  		/*
  		 * If we were the last child thread and the leader has
  		 * exited already, and the leader's parent ignores SIGCHLD,
  		 * then we are the one who should release the leader.
  		 *
  		 * do_notify_parent() will have marked it self-reaping in
  		 * that case.
  		 */

  		zap_leader = task_detached(leader);

  
  		/*
  		 * This maintains the invariant that release_task()
  		 * only runs on a task in EXIT_DEAD, just for sanity.
  		 */
  		if (zap_leader)
  			leader->exit_state = EXIT_DEAD;

  	}

  	write_unlock_irq(&tasklist_lock);

  	release_thread(p);

  	call_rcu(&p->rcu, delayed_put_task_struct);

  
  	p = leader;
  	if (unlikely(zap_leader))
  		goto repeat;
  }

  /*
   * This checks not only the pgrp, but falls back on the pid if no
   * satisfactory pgrp is found. I dunno - gdb doesn't work correctly
   * without this...

   *
   * The caller must hold rcu lock or the tasklist lock.

   */

  struct pid *session_of_pgrp(struct pid *pgrp)

  {
  	struct task_struct *p;

  	struct pid *sid = NULL;

  	p = pid_task(pgrp, PIDTYPE_PGID);

  	if (p == NULL)

  		p = pid_task(pgrp, PIDTYPE_PID);

  	if (p != NULL)

  		sid = task_session(p);

  	return sid;
  }
  
  /*
   * Determine if a process group is "orphaned", according to the POSIX
   * definition in 2.2.2.52.  Orphaned process groups are not to be affected
   * by terminal-generated stop signals.  Newly orphaned process groups are
   * to receive a SIGHUP and a SIGCONT.
   *
   * "I ask you, have you ever known what it is to be an orphan?"
   */

  static int will_become_orphaned_pgrp(struct pid *pgrp, struct task_struct *ignored_task)

  {
  	struct task_struct *p;

  	do_each_pid_task(pgrp, PIDTYPE_PGID, p) {

  		if ((p == ignored_task) ||
  		    (p->exit_state && thread_group_empty(p)) ||
  		    is_global_init(p->real_parent))

  			continue;

  		if (task_pgrp(p->real_parent) != pgrp &&

  		    task_session(p->real_parent) == task_session(p))
  			return 0;

  	} while_each_pid_task(pgrp, PIDTYPE_PGID, p);

  
  	return 1;

  }

  int is_current_pgrp_orphaned(void)

  {
  	int retval;
  
  	read_lock(&tasklist_lock);

  	retval = will_become_orphaned_pgrp(task_pgrp(current), NULL);

  	read_unlock(&tasklist_lock);
  
  	return retval;
  }

  static int has_stopped_jobs(struct pid *pgrp)

  {
  	int retval = 0;
  	struct task_struct *p;

  	do_each_pid_task(pgrp, PIDTYPE_PGID, p) {

  		if (!task_is_stopped(p))

  			continue;

  		retval = 1;
  		break;

  	} while_each_pid_task(pgrp, PIDTYPE_PGID, p);

  	return retval;
  }

  /*
   * Check to see if any process groups have become orphaned as
   * a result of our exiting, and if they have any stopped jobs,
   * send them a SIGHUP and then a SIGCONT. (POSIX 3.2.2.2)
   */
  static void
  kill_orphaned_pgrp(struct task_struct *tsk, struct task_struct *parent)
  {
  	struct pid *pgrp = task_pgrp(tsk);
  	struct task_struct *ignored_task = tsk;
  
  	if (!parent)
  		 /* exit: our father is in a different pgrp than
  		  * we are and we were the only connection outside.
  		  */
  		parent = tsk->real_parent;
  	else
  		/* reparent: our child is in a different pgrp than
  		 * we are, and it was the only connection outside.
  		 */
  		ignored_task = NULL;
  
  	if (task_pgrp(parent) != pgrp &&
  	    task_session(parent) == task_session(tsk) &&
  	    will_become_orphaned_pgrp(pgrp, ignored_task) &&
  	    has_stopped_jobs(pgrp)) {
  		__kill_pgrp_info(SIGHUP, SEND_SIG_PRIV, pgrp);
  		__kill_pgrp_info(SIGCONT, SEND_SIG_PRIV, pgrp);
  	}
  }

  /**

   * reparent_to_kthreadd - Reparent the calling kernel thread to kthreadd

   *
   * If a kernel thread is launched as a result of a system call, or if

   * it ever exits, it should generally reparent itself to kthreadd so it
   * isn't in the way of other processes and is correctly cleaned up on exit.

   *
   * The various task state such as scheduling policy and priority may have
   * been inherited from a user process, so we reset them to sane values here.
   *

   * NOTE that reparent_to_kthreadd() gives the caller full capabilities.

   */

  static void reparent_to_kthreadd(void)

  {
  	write_lock_irq(&tasklist_lock);
  
  	ptrace_unlink(current);
  	/* Reparent to init */

  	current->real_parent = current->parent = kthreadd_task;

  	list_move_tail(&current->sibling, &current->real_parent->children);

  
  	/* Set the exit signal to SIGCHLD so we signal init on exit */
  	current->exit_signal = SIGCHLD;

  	if (task_nice(current) < 0)

  		set_user_nice(current, 0);
  	/* cpus_allowed? */
  	/* rt_priority? */
  	/* signals? */

  	memcpy(current->signal->rlim, init_task.signal->rlim,
  	       sizeof(current->signal->rlim));

  
  	atomic_inc(&init_cred.usage);
  	commit_creds(&init_cred);

  	write_unlock_irq(&tasklist_lock);

  }

  void __set_special_pids(struct pid *pid)

  {

  	struct task_struct *curr = current->group_leader;

  	if (task_session(curr) != pid)

  		change_pid(curr, PIDTYPE_SID, pid);

  
  	if (task_pgrp(curr) != pid)

  		change_pid(curr, PIDTYPE_PGID, pid);

  }

  static void set_special_pids(struct pid *pid)

  {
  	write_lock_irq(&tasklist_lock);

  	__set_special_pids(pid);

  	write_unlock_irq(&tasklist_lock);
  }
  
  /*

   * Let kernel threads use this to say that they allow a certain signal.
   * Must not be used if kthread was cloned with CLONE_SIGHAND.

   */
  int allow_signal(int sig)
  {

  	if (!valid_signal(sig) || sig < 1)

  		return -EINVAL;
  
  	spin_lock_irq(&current->sighand->siglock);

  	/* This is only needed for daemonize()'ed kthreads */

  	sigdelset(&current->blocked, sig);

  	/*
  	 * Kernel threads handle their own signals. Let the signal code
  	 * know it'll be handled, so that they don't get converted to
  	 * SIGKILL or just silently dropped.
  	 */
  	current->sighand->action[(sig)-1].sa.sa_handler = (void __user *)2;

  	recalc_sigpending();
  	spin_unlock_irq(&current->sighand->siglock);
  	return 0;
  }
  
  EXPORT_SYMBOL(allow_signal);
  
  int disallow_signal(int sig)
  {

  	if (!valid_signal(sig) || sig < 1)

  		return -EINVAL;
  
  	spin_lock_irq(&current->sighand->siglock);

  	current->sighand->action[(sig)-1].sa.sa_handler = SIG_IGN;

  	recalc_sigpending();
  	spin_unlock_irq(&current->sighand->siglock);
  	return 0;
  }
  
  EXPORT_SYMBOL(disallow_signal);
  
  /*
   *	Put all the gunge required to become a kernel thread without
   *	attached user resources in one place where it belongs.
   */
  
  void daemonize(const char *name, ...)
  {
  	va_list args;

  	sigset_t blocked;
  
  	va_start(args, name);
  	vsnprintf(current->comm, sizeof(current->comm), name, args);
  	va_end(args);
  
  	/*
  	 * If we were started as result of loading a module, close all of the
  	 * user space pages.  We don't need them, and if we didn't close them
  	 * they would be locked into memory.
  	 */
  	exit_mm(current);

  	/*
  	 * We don't want to have TIF_FREEZE set if the system-wide hibernation
  	 * or suspend transition begins right now.
  	 */

  	current->flags |= (PF_NOFREEZE | PF_KTHREAD);

  	if (current->nsproxy != &init_nsproxy) {
  		get_nsproxy(&init_nsproxy);
  		switch_task_namespaces(current, &init_nsproxy);
  	}

  	set_special_pids(&init_struct_pid);

  	proc_clear_tty(current);

  
  	/* Block and flush all signals */
  	sigfillset(&blocked);
  	sigprocmask(SIG_BLOCK, &blocked, NULL);
  	flush_signals(current);
  
  	/* Become as one with the init task */

  	daemonize_fs_struct();

  	exit_files(current);

  	current->files = init_task.files;
  	atomic_inc(&current->files->count);

  	reparent_to_kthreadd();

  }
  
  EXPORT_SYMBOL(daemonize);

  static void close_files(struct files_struct * files)

  {
  	int i, j;

  	struct fdtable *fdt;

  
  	j = 0;

  
  	/*
  	 * It is safe to dereference the fd table without RCU or
  	 * ->file_lock because this is the last reference to the

  	 * files structure.  But use RCU to shut RCU-lockdep up.

  	 */

  	rcu_read_lock();

  	fdt = files_fdtable(files);

  	rcu_read_unlock();

  	for (;;) {
  		unsigned long set;
  		i = j * __NFDBITS;

  		if (i >= fdt->max_fds)

  			break;

  		set = fdt->open_fds->fds_bits[j++];

  		while (set) {
  			if (set & 1) {

  				struct file * file = xchg(&fdt->fd[i], NULL);

  				if (file) {

  					filp_close(file, files);

  					cond_resched();
  				}

  			}
  			i++;
  			set >>= 1;
  		}
  	}
  }
  
  struct files_struct *get_files_struct(struct task_struct *task)
  {
  	struct files_struct *files;
  
  	task_lock(task);
  	files = task->files;
  	if (files)
  		atomic_inc(&files->count);
  	task_unlock(task);
  
  	return files;
  }

  void put_files_struct(struct files_struct *files)

  {

  	struct fdtable *fdt;

  	if (atomic_dec_and_test(&files->count)) {
  		close_files(files);
  		/*
  		 * Free the fd and fdset arrays if we expanded them.

  		 * If the fdtable was embedded, pass files for freeing
  		 * at the end of the RCU grace period. Otherwise,
  		 * you can free files immediately.

  		 */

  		rcu_read_lock();

  		fdt = files_fdtable(files);

  		if (fdt != &files->fdtab)

  			kmem_cache_free(files_cachep, files);

  		free_fdtable(fdt);

  		rcu_read_unlock();

  	}
  }

  void reset_files_struct(struct files_struct *files)

  {

  	struct task_struct *tsk = current;

  	struct files_struct *old;
  
  	old = tsk->files;
  	task_lock(tsk);
  	tsk->files = files;
  	task_unlock(tsk);
  	put_files_struct(old);
  }

  void exit_files(struct task_struct *tsk)

  {
  	struct files_struct * files = tsk->files;
  
  	if (files) {
  		task_lock(tsk);
  		tsk->files = NULL;
  		task_unlock(tsk);
  		put_files_struct(files);
  	}
  }

  #ifdef CONFIG_MM_OWNER
  /*
   * Task p is exiting and it owned mm, lets find a new owner for it
   */
  static inline int
  mm_need_new_owner(struct mm_struct *mm, struct task_struct *p)
  {
  	/*
  	 * If there are other users of the mm and the owner (us) is exiting
  	 * we need to find a new owner to take on the responsibility.
  	 */

  	if (atomic_read(&mm->mm_users) <= 1)
  		return 0;
  	if (mm->owner != p)
  		return 0;
  	return 1;
  }
  
  void mm_update_next_owner(struct mm_struct *mm)
  {
  	struct task_struct *c, *g, *p = current;
  
  retry:
  	if (!mm_need_new_owner(mm, p))
  		return;
  
  	read_lock(&tasklist_lock);
  	/*
  	 * Search in the children
  	 */
  	list_for_each_entry(c, &p->children, sibling) {
  		if (c->mm == mm)
  			goto assign_new_owner;
  	}
  
  	/*
  	 * Search in the siblings
  	 */

  	list_for_each_entry(c, &p->real_parent->children, sibling) {

  		if (c->mm == mm)
  			goto assign_new_owner;
  	}
  
  	/*
  	 * Search through everything else. We should not get
  	 * here often
  	 */
  	do_each_thread(g, c) {
  		if (c->mm == mm)
  			goto assign_new_owner;
  	} while_each_thread(g, c);
  
  	read_unlock(&tasklist_lock);

  	/*
  	 * We found no owner yet mm_users > 1: this implies that we are
  	 * most likely racing with swapoff (try_to_unuse()) or /proc or

  	 * ptrace or page migration (get_task_mm()).  Mark owner as NULL.

  	 */

  	mm->owner = NULL;

  	return;
  
  assign_new_owner:
  	BUG_ON(c == p);
  	get_task_struct(c);
  	/*
  	 * The task_lock protects c->mm from changing.
  	 * We always want mm->owner->mm == mm
  	 */
  	task_lock(c);

  	/*
  	 * Delay read_unlock() till we have the task_lock()
  	 * to ensure that c does not slip away underneath us
  	 */
  	read_unlock(&tasklist_lock);

  	if (c->mm != mm) {
  		task_unlock(c);
  		put_task_struct(c);
  		goto retry;
  	}

  	mm->owner = c;
  	task_unlock(c);
  	put_task_struct(c);
  }
  #endif /* CONFIG_MM_OWNER */

  /*
   * Turn us into a lazy TLB process if we
   * aren't already..
   */

  static void exit_mm(struct task_struct * tsk)

  {
  	struct mm_struct *mm = tsk->mm;

  	struct core_state *core_state;

  
  	mm_release(tsk, mm);
  	if (!mm)
  		return;
  	/*
  	 * Serialize with any possible pending coredump.

  	 * We must hold mmap_sem around checking core_state

  	 * and clearing tsk->mm.  The core-inducing thread

  	 * will increment ->nr_threads for each thread in the

  	 * group with ->mm != NULL.
  	 */
  	down_read(&mm->mmap_sem);

  	core_state = mm->core_state;
  	if (core_state) {
  		struct core_thread self;

  		up_read(&mm->mmap_sem);

  		self.task = tsk;
  		self.next = xchg(&core_state->dumper.next, &self);
  		/*
  		 * Implies mb(), the result of xchg() must be visible
  		 * to core_state->dumper.
  		 */
  		if (atomic_dec_and_test(&core_state->nr_threads))
  			complete(&core_state->startup);

  		for (;;) {
  			set_task_state(tsk, TASK_UNINTERRUPTIBLE);
  			if (!self.task) /* see coredump_finish() */
  				break;
  			schedule();
  		}
  		__set_task_state(tsk, TASK_RUNNING);

  		down_read(&mm->mmap_sem);
  	}
  	atomic_inc(&mm->mm_count);

  	BUG_ON(mm != tsk->active_mm);

  	/* more a memory barrier than a real lock */
  	task_lock(tsk);
  	tsk->mm = NULL;
  	up_read(&mm->mmap_sem);
  	enter_lazy_tlb(mm, current);

  	/* We don't want this task to be frozen prematurely */
  	clear_freeze_flag(tsk);

  	if (tsk->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
  		atomic_dec(&mm->oom_disable_count);

  	task_unlock(tsk);

  	mm_update_next_owner(mm);

  	mmput(mm);
  }

  /*
   * When we die, we re-parent all our children.
   * Try to give them to another thread in our thread
   * group, and if no such member exists, give it to

   * the child reaper process (ie "init") in our pid
   * space.

   */

  static struct task_struct *find_new_reaper(struct task_struct *father)

  	__releases(&tasklist_lock)
  	__acquires(&tasklist_lock)

  {

  	struct pid_namespace *pid_ns = task_active_pid_ns(father);
  	struct task_struct *thread;

  	thread = father;
  	while_each_thread(father, thread) {
  		if (thread->flags & PF_EXITING)
  			continue;
  		if (unlikely(pid_ns->child_reaper == father))
  			pid_ns->child_reaper = thread;
  		return thread;
  	}

  	if (unlikely(pid_ns->child_reaper == father)) {
  		write_unlock_irq(&tasklist_lock);
  		if (unlikely(pid_ns == &init_pid_ns))
  			panic("Attempted to kill init!");

  		zap_pid_ns_processes(pid_ns);
  		write_lock_irq(&tasklist_lock);

  		/*

  		 * We can not clear ->child_reaper or leave it alone.
  		 * There may by stealth EXIT_DEAD tasks on ->children,
  		 * forget_original_parent() must move them somewhere.

  		 */

  		pid_ns->child_reaper = init_pid_ns.child_reaper;

  	}

  	return pid_ns->child_reaper;
  }

  /*
  * Any that need to be release_task'd are put on the @dead list.
   */

  static void reparent_leader(struct task_struct *father, struct task_struct *p,

  				struct list_head *dead)
  {

  	list_move_tail(&p->sibling, &p->real_parent->children);
  
  	if (task_detached(p))
  		return;
  	/*
  	 * If this is a threaded reparent there is no need to
  	 * notify anyone anything has happened.
  	 */
  	if (same_thread_group(p->real_parent, father))
  		return;
  
  	/* We don't want people slaying init.  */
  	p->exit_signal = SIGCHLD;
  
  	/* If it has exited notify the new parent about this child's death. */

  	if (!task_ptrace(p) &&

  	    p->exit_state == EXIT_ZOMBIE && thread_group_empty(p)) {
  		do_notify_parent(p, p->exit_signal);
  		if (task_detached(p)) {
  			p->exit_state = EXIT_DEAD;
  			list_move_tail(&p->sibling, dead);
  		}
  	}
  
  	kill_orphaned_pgrp(p, father);
  }

  static void forget_original_parent(struct task_struct *father)

  {

  	struct task_struct *p, *n, *reaper;

  	LIST_HEAD(dead_children);

  
  	write_lock_irq(&tasklist_lock);

  	/*
  	 * Note that exit_ptrace() and find_new_reaper() might
  	 * drop tasklist_lock and reacquire it.
  	 */
  	exit_ptrace(father);

  	reaper = find_new_reaper(father);

  	list_for_each_entry_safe(p, n, &father->children, sibling) {

  		struct task_struct *t = p;
  		do {
  			t->real_parent = reaper;
  			if (t->parent == father) {
  				BUG_ON(task_ptrace(t));
  				t->parent = t->real_parent;
  			}
  			if (t->pdeath_signal)
  				group_send_sig_info(t->pdeath_signal,
  						    SEND_SIG_NOINFO, t);
  		} while_each_thread(p, t);
  		reparent_leader(father, p, &dead_children);

  	}

  	write_unlock_irq(&tasklist_lock);

  	BUG_ON(!list_empty(&father->children));

  	list_for_each_entry_safe(p, n, &dead_children, sibling) {
  		list_del_init(&p->sibling);

  		release_task(p);
  	}

  }
  
  /*
   * Send signals to all our closest relatives so that they know
   * to properly mourn us..
   */

  static void exit_notify(struct task_struct *tsk, int group_dead)

  {

  	int signal;
  	void *cookie;

  	/*
  	 * This does two things:
  	 *
    	 * A.  Make init inherit all the child processes
  	 * B.  Check to see if any process groups have become orphaned
  	 *	as a result of our exiting, and if they have any stopped
  	 *	jobs, send them a SIGHUP and then a SIGCONT.  (POSIX 3.2.2.2)
  	 */

  	forget_original_parent(tsk);

  	exit_task_namespaces(tsk);

  	write_lock_irq(&tasklist_lock);

  	if (group_dead)
  		kill_orphaned_pgrp(tsk->group_leader, NULL);

  	/* Let father know we died

  	 *
  	 * Thread signals are configurable, but you aren't going to use

  	 * that to send signals to arbitrary processes.

  	 * That stops right now.
  	 *
  	 * If the parent exec id doesn't match the exec id we saved
  	 * when we started then we know the parent has changed security
  	 * domain.
  	 *
  	 * If our self_exec id doesn't match our parent_exec_id then
  	 * we have changed execution domain as these two values started
  	 * the same after a fork.

  	 */

  	if (tsk->exit_signal != SIGCHLD && !task_detached(tsk) &&

  	    (tsk->parent_exec_id != tsk->real_parent->self_exec_id ||

  	     tsk->self_exec_id != tsk->parent_exec_id))

  		tsk->exit_signal = SIGCHLD;

  	signal = tracehook_notify_death(tsk, &cookie, group_dead);

  	if (signal >= 0)

  		signal = do_notify_parent(tsk, signal);

  	tsk->exit_state = signal == DEATH_REAP ? EXIT_DEAD : EXIT_ZOMBIE;

  	/* mt-exec, de_thread() is waiting for group leader */
  	if (unlikely(tsk->signal->notify_count < 0))

  		wake_up_process(tsk->signal->group_exit_task);

  	write_unlock_irq(&tasklist_lock);

  	tracehook_report_death(tsk, signal, cookie, group_dead);

  	/* If the process is dead, release it - nobody will wait for it */

  	if (signal == DEATH_REAP)

  		release_task(tsk);

  }

  #ifdef CONFIG_DEBUG_STACK_USAGE
  static void check_stack_usage(void)
  {
  	static DEFINE_SPINLOCK(low_water_lock);
  	static int lowest_to_date = THREAD_SIZE;

  	unsigned long free;

  	free = stack_not_used(current);

  
  	if (free >= lowest_to_date)
  		return;
  
  	spin_lock(&low_water_lock);
  	if (free < lowest_to_date) {
  		printk(KERN_WARNING "%s used greatest stack depth: %lu bytes "
  				"left
  ",
  				current->comm, free);
  		lowest_to_date = free;
  	}
  	spin_unlock(&low_water_lock);
  }
  #else
  static inline void check_stack_usage(void) {}
  #endif

  NORET_TYPE void do_exit(long code)

  {
  	struct task_struct *tsk = current;
  	int group_dead;
  
  	profile_task_exit(tsk);

  	WARN_ON(atomic_read(&tsk->fs_excl));

  	WARN_ON(blk_needs_flush_plug(tsk));

  	if (unlikely(in_interrupt()))
  		panic("Aiee, killing interrupt handler!");
  	if (unlikely(!tsk->pid))
  		panic("Attempted to kill the idle task!");

  	/*
  	 * If do_exit is called because this processes oopsed, it's possible
  	 * that get_fs() was left as KERNEL_DS, so reset it to USER_DS before
  	 * continuing. Amongst other possible reasons, this is to prevent
  	 * mm_release()->clear_child_tid() from writing to a user-controlled
  	 * kernel address.
  	 */
  	set_fs(USER_DS);

  	tracehook_report_exit(&code);

  	validate_creds_for_do_exit(tsk);

  	/*
  	 * We're taking recursive faults here in do_exit. Safest is to just
  	 * leave this task alone and wait for reboot.
  	 */
  	if (unlikely(tsk->flags & PF_EXITING)) {
  		printk(KERN_ALERT
  			"Fixing recursive fault but reboot is needed!
  ");

  		/*
  		 * We can do this unlocked here. The futex code uses
  		 * this flag just to verify whether the pi state
  		 * cleanup has been done or not. In the worst case it
  		 * loops once more. We pretend that the cleanup was
  		 * done as there is no way to return. Either the
  		 * OWNER_DIED bit is set by now or we push the blocked
  		 * task into the wait for ever nirwana as well.
  		 */
  		tsk->flags |= PF_EXITPIDONE;

  		set_current_state(TASK_UNINTERRUPTIBLE);
  		schedule();
  	}

  	exit_irq_thread();

  	exit_signals(tsk);  /* sets PF_EXITING */

  	/*
  	 * tsk->flags are checked in the futex code to protect against
  	 * an exiting task cleaning up the robust pi futexes.
  	 */

  	smp_mb();

  	raw_spin_unlock_wait(&tsk->pi_lock);

  	if (unlikely(in_atomic()))
  		printk(KERN_INFO "note: %s[%d] exited with preempt_count %d
  ",

  				current->comm, task_pid_nr(current),

  				preempt_count());
  
  	acct_update_integrals(tsk);

  	/* sync mm's RSS info before statistics gathering */

  	if (tsk->mm)
  		sync_mm_rss(tsk, tsk->mm);

  	group_dead = atomic_dec_and_test(&tsk->signal->live);

  	if (group_dead) {

  		hrtimer_cancel(&tsk->signal->real_timer);

  		exit_itimers(tsk->signal);

  		if (tsk->mm)
  			setmax_mm_hiwater_rss(&tsk->signal->maxrss, tsk->mm);

  	}

  	acct_collect(code, group_dead);

  	if (group_dead)
  		tty_audit_exit();

  	if (unlikely(tsk->audit_context))
  		audit_free(tsk);

  	tsk->exit_code = code;

  	taskstats_exit(tsk, group_dead);

  	exit_mm(tsk);

  	if (group_dead)

  		acct_process();

  	trace_sched_process_exit(tsk);

  	exit_sem(tsk);

  	exit_files(tsk);
  	exit_fs(tsk);

  	check_stack_usage();

  	exit_thread();

  
  	/*
  	 * Flush inherited counters to the parent - before the parent
  	 * gets woken up by child-exit notifications.
  	 *
  	 * because of cgroup mode, must be called before cgroup_exit()
  	 */
  	perf_event_exit_task(tsk);

  	cgroup_exit(tsk, 1);

  	if (group_dead)

  		disassociate_ctty(1);

  	module_put(task_thread_info(tsk)->exec_domain->module);

  	proc_exit_connector(tsk);

  
  	/*

  	 * FIXME: do that only when needed, using sched_exit tracepoint
  	 */

  	ptrace_put_breakpoints(tsk);

  	exit_notify(tsk, group_dead);

  #ifdef CONFIG_NUMA

  	task_lock(tsk);

  	mpol_put(tsk->mempolicy);

  	tsk->mempolicy = NULL;

  	task_unlock(tsk);

  #endif

  #ifdef CONFIG_FUTEX

  	if (unlikely(current->pi_state_cache))
  		kfree(current->pi_state_cache);

  #endif

  	/*

  	 * Make sure we are holding no locks:

  	 */

  	debug_check_no_locks_held(tsk);

  	/*
  	 * We can do this unlocked here. The futex code uses this flag
  	 * just to verify whether the pi state cleanup has been done
  	 * or not. In the worst case it loops once more.
  	 */
  	tsk->flags |= PF_EXITPIDONE;

  	if (tsk->io_context)

  		exit_io_context(tsk);

  	if (tsk->splice_pipe)
  		__free_pipe_info(tsk->splice_pipe);

  	validate_creds_for_do_exit(tsk);

  	preempt_disable();

  	exit_rcu();

  	/* causes final put_task_struct in finish_task_switch(). */

  	tsk->state = TASK_DEAD;

  	schedule();
  	BUG();
  	/* Avoid "noreturn function does return".  */

  	for (;;)
  		cpu_relax();	/* For when BUG is null */

  }

  EXPORT_SYMBOL_GPL(do_exit);

  NORET_TYPE void complete_and_exit(struct completion *comp, long code)
  {
  	if (comp)
  		complete(comp);

  	do_exit(code);
  }
  
  EXPORT_SYMBOL(complete_and_exit);

  SYSCALL_DEFINE1(exit, int, error_code)

  {
  	do_exit((error_code&0xff)<<8);
  }

  /*
   * Take down every thread in the group.  This is called by fatal signals
   * as well as by sys_exit_group (below).
   */
  NORET_TYPE void
  do_group_exit(int exit_code)
  {

  	struct signal_struct *sig = current->signal;

  	BUG_ON(exit_code & 0x80); /* core dumps don't get here */

  	if (signal_group_exit(sig))
  		exit_code = sig->group_exit_code;

  	else if (!thread_group_empty(current)) {

  		struct sighand_struct *const sighand = current->sighand;

  		spin_lock_irq(&sighand->siglock);

  		if (signal_group_exit(sig))

  			/* Another thread got here before we took the lock.  */
  			exit_code = sig->group_exit_code;
  		else {

  			sig->group_exit_code = exit_code;

  			sig->flags = SIGNAL_GROUP_EXIT;

  			zap_other_threads(current);
  		}
  		spin_unlock_irq(&sighand->siglock);

  	}
  
  	do_exit(exit_code);
  	/* NOTREACHED */
  }
  
  /*
   * this kills every thread in the thread group. Note that any externally
   * wait4()-ing process will get the correct exit code - even if this
   * thread is not the thread group leader.
   */

  SYSCALL_DEFINE1(exit_group, int, error_code)

  {
  	do_group_exit((error_code & 0xff) << 8);

  	/* NOTREACHED */
  	return 0;

  }

  struct wait_opts {
  	enum pid_type		wo_type;

  	int			wo_flags;

  	struct pid		*wo_pid;

  
  	struct siginfo __user	*wo_info;
  	int __user		*wo_stat;
  	struct rusage __user	*wo_rusage;

  	wait_queue_t		child_wait;

  	int			notask_error;
  };

  static inline
  struct pid *task_pid_type(struct task_struct *task, enum pid_type type)

  {

  	if (type != PIDTYPE_PID)
  		task = task->group_leader;
  	return task->pids[type].pid;

  }

  static int eligible_pid(struct wait_opts *wo, struct task_struct *p)

  {

  	return	wo->wo_type == PIDTYPE_MAX ||
  		task_pid_type(p, wo->wo_type) == wo->wo_pid;
  }

  static int eligible_child(struct wait_opts *wo, struct task_struct *p)
  {
  	if (!eligible_pid(wo, p))
  		return 0;

  	/* Wait for all children (clone and not) if __WALL is set;
  	 * otherwise, wait for clone children *only* if __WCLONE is
  	 * set; otherwise, wait for non-clone children *only*.  (Note:
  	 * A "clone" child here is one that reports to its parent
  	 * using a signal other than SIGCHLD.) */

  	if (((p->exit_signal != SIGCHLD) ^ !!(wo->wo_flags & __WCLONE))
  	    && !(wo->wo_flags & __WALL))

  		return 0;

  	return 1;

  }

  static int wait_noreap_copyout(struct wait_opts *wo, struct task_struct *p,
  				pid_t pid, uid_t uid, int why, int status)

  {

  	struct siginfo __user *infop;
  	int retval = wo->wo_rusage
  		? getrusage(p, RUSAGE_BOTH, wo->wo_rusage) : 0;

  	put_task_struct(p);

  	infop = wo->wo_info;

  	if (infop) {
  		if (!retval)
  			retval = put_user(SIGCHLD, &infop->si_signo);
  		if (!retval)
  			retval = put_user(0, &infop->si_errno);
  		if (!retval)
  			retval = put_user((short)why, &infop->si_code);
  		if (!retval)
  			retval = put_user(pid, &infop->si_pid);
  		if (!retval)
  			retval = put_user(uid, &infop->si_uid);
  		if (!retval)
  			retval = put_user(status, &infop->si_status);
  	}

  	if (!retval)
  		retval = pid;
  	return retval;
  }
  
  /*
   * Handle sys_wait4 work for one task in state EXIT_ZOMBIE.  We hold
   * read_lock(&tasklist_lock) on entry.  If we return zero, we still hold
   * the lock and this task is uninteresting.  If we return nonzero, we have
   * released the lock and the system call should return.
   */

  static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)

  {
  	unsigned long state;

  	int retval, status, traced;

  	pid_t pid = task_pid_vnr(p);

  	uid_t uid = __task_cred(p)->uid;

  	struct siginfo __user *infop;

  	if (!likely(wo->wo_flags & WEXITED))

  		return 0;

  	if (unlikely(wo->wo_flags & WNOWAIT)) {

  		int exit_code = p->exit_code;

  		int why;

  		get_task_struct(p);
  		read_unlock(&tasklist_lock);
  		if ((exit_code & 0x7f) == 0) {
  			why = CLD_EXITED;
  			status = exit_code >> 8;
  		} else {
  			why = (exit_code & 0x80) ? CLD_DUMPED : CLD_KILLED;
  			status = exit_code & 0x7f;
  		}

  		return wait_noreap_copyout(wo, p, pid, uid, why, status);

  	}
  
  	/*
  	 * Try to move the task's state to DEAD
  	 * only one thread is allowed to do this:
  	 */
  	state = xchg(&p->exit_state, EXIT_DEAD);
  	if (state != EXIT_ZOMBIE) {
  		BUG_ON(state != EXIT_DEAD);
  		return 0;
  	}

  	traced = ptrace_reparented(p);

  	/*
  	 * It can be ptraced but not reparented, check
  	 * !task_detached() to filter out sub-threads.
  	 */
  	if (likely(!traced) && likely(!task_detached(p))) {

  		struct signal_struct *psig;
  		struct signal_struct *sig;

  		unsigned long maxrss;

  		cputime_t tgutime, tgstime;

  		/*
  		 * The resource counters for the group leader are in its
  		 * own task_struct.  Those for dead threads in the group
  		 * are in its signal_struct, as are those for the child
  		 * processes it has previously reaped.  All these
  		 * accumulate in the parent's signal_struct c* fields.
  		 *
  		 * We don't bother to take a lock here to protect these
  		 * p->signal fields, because they are only touched by
  		 * __exit_signal, which runs with tasklist_lock
  		 * write-locked anyway, and so is excluded here.  We do

  		 * need to protect the access to parent->signal fields,

  		 * as other threads in the parent group can be right
  		 * here reaping other children at the same time.

  		 *
  		 * We use thread_group_times() to get times for the thread
  		 * group, which consolidates times for all threads in the
  		 * group including the group leader.

  		 */

  		thread_group_times(p, &tgutime, &tgstime);

  		spin_lock_irq(&p->real_parent->sighand->siglock);
  		psig = p->real_parent->signal;

  		sig = p->signal;
  		psig->cutime =
  			cputime_add(psig->cutime,

  			cputime_add(tgutime,
  				    sig->cutime));

  		psig->cstime =
  			cputime_add(psig->cstime,

  			cputime_add(tgstime,
  				    sig->cstime));

  		psig->cgtime =
  			cputime_add(psig->cgtime,
  			cputime_add(p->gtime,
  			cputime_add(sig->gtime,
  				    sig->cgtime)));

  		psig->cmin_flt +=
  			p->min_flt + sig->min_flt + sig->cmin_flt;
  		psig->cmaj_flt +=
  			p->maj_flt + sig->maj_flt + sig->cmaj_flt;
  		psig->cnvcsw +=
  			p->nvcsw + sig->nvcsw + sig->cnvcsw;
  		psig->cnivcsw +=
  			p->nivcsw + sig->nivcsw + sig->cnivcsw;

  		psig->cinblock +=
  			task_io_get_inblock(p) +
  			sig->inblock + sig->cinblock;
  		psig->coublock +=
  			task_io_get_oublock(p) +
  			sig->oublock + sig->coublock;

  		maxrss = max(sig->maxrss, sig->cmaxrss);
  		if (psig->cmaxrss < maxrss)
  			psig->cmaxrss = maxrss;

  		task_io_accounting_add(&psig->ioac, &p->ioac);
  		task_io_accounting_add(&psig->ioac, &sig->ioac);

  		spin_unlock_irq(&p->real_parent->sighand->siglock);

  	}
  
  	/*
  	 * Now we are sure this task is interesting, and no other
  	 * thread can reap it because we set its state to EXIT_DEAD.
  	 */
  	read_unlock(&tasklist_lock);

  	retval = wo->wo_rusage
  		? getrusage(p, RUSAGE_BOTH, wo->wo_rusage) : 0;

  	status = (p->signal->flags & SIGNAL_GROUP_EXIT)
  		? p->signal->group_exit_code : p->exit_code;

  	if (!retval && wo->wo_stat)
  		retval = put_user(status, wo->wo_stat);
  
  	infop = wo->wo_info;

  	if (!retval && infop)
  		retval = put_user(SIGCHLD, &infop->si_signo);
  	if (!retval && infop)
  		retval = put_user(0, &infop->si_errno);
  	if (!retval && infop) {
  		int why;
  
  		if ((status & 0x7f) == 0) {
  			why = CLD_EXITED;
  			status >>= 8;
  		} else {
  			why = (status & 0x80) ? CLD_DUMPED : CLD_KILLED;
  			status &= 0x7f;
  		}
  		retval = put_user((short)why, &infop->si_code);
  		if (!retval)
  			retval = put_user(status, &infop->si_status);
  	}
  	if (!retval && infop)

  		retval = put_user(pid, &infop->si_pid);

  	if (!retval && infop)

  		retval = put_user(uid, &infop->si_uid);

  	if (!retval)

  		retval = pid;

  
  	if (traced) {

  		write_lock_irq(&tasklist_lock);

  		/* We dropped tasklist, ptracer could die and untrace */
  		ptrace_unlink(p);
  		/*
  		 * If this is not a detached task, notify the parent.
  		 * If it's still not detached after that, don't release
  		 * it now.
  		 */

  		if (!task_detached(p)) {

  			do_notify_parent(p, p->exit_signal);

  			if (!task_detached(p)) {

  				p->exit_state = EXIT_ZOMBIE;
  				p = NULL;

  			}
  		}
  		write_unlock_irq(&tasklist_lock);
  	}
  	if (p != NULL)
  		release_task(p);

  	return retval;
  }

  static int *task_stopped_code(struct task_struct *p, bool ptrace)
  {
  	if (ptrace) {
  		if (task_is_stopped_or_traced(p))
  			return &p->exit_code;
  	} else {
  		if (p->signal->flags & SIGNAL_STOP_STOPPED)
  			return &p->signal->group_exit_code;
  	}
  	return NULL;
  }

  /*
   * Handle sys_wait4 work for one task in state TASK_STOPPED.  We hold
   * read_lock(&tasklist_lock) on entry.  If we return zero, we still hold
   * the lock and this task is uninteresting.  If we return nonzero, we have
   * released the lock and the system call should return.
   */

  static int wait_task_stopped(struct wait_opts *wo,
  				int ptrace, struct task_struct *p)

  {

  	struct siginfo __user *infop;

  	int retval, exit_code, *p_code, why;

  	uid_t uid = 0; /* unneeded, required by compiler */

  	pid_t pid;

  	/*
  	 * Traditionally we see ptrace'd stopped tasks regardless of options.
  	 */

  	if (!ptrace && !(wo->wo_flags & WUNTRACED))

  		return 0;

  	exit_code = 0;
  	spin_lock_irq(&p->sighand->siglock);

  	p_code = task_stopped_code(p, ptrace);
  	if (unlikely(!p_code))

  		goto unlock_sig;

  	exit_code = *p_code;

  	if (!exit_code)
  		goto unlock_sig;

  	if (!unlikely(wo->wo_flags & WNOWAIT))

  		*p_code = 0;

  	uid = task_uid(p);

  unlock_sig:
  	spin_unlock_irq(&p->sighand->siglock);
  	if (!exit_code)

  		return 0;
  
  	/*
  	 * Now we are pretty sure this task is interesting.
  	 * Make sure it doesn't get reaped out from under us while we
  	 * give up the lock and then examine it below.  We don't want to
  	 * keep holding onto the tasklist_lock while we call getrusage and
  	 * possibly take page faults for user memory.
  	 */
  	get_task_struct(p);

  	pid = task_pid_vnr(p);

  	why = ptrace ? CLD_TRAPPED : CLD_STOPPED;

  	read_unlock(&tasklist_lock);

  	if (unlikely(wo->wo_flags & WNOWAIT))
  		return wait_noreap_copyout(wo, p, pid, uid, why, exit_code);
  
  	retval = wo->wo_rusage
  		? getrusage(p, RUSAGE_BOTH, wo->wo_rusage) : 0;
  	if (!retval && wo->wo_stat)
  		retval = put_user((exit_code << 8) | 0x7f, wo->wo_stat);

  	infop = wo->wo_info;

  	if (!retval && infop)
  		retval = put_user(SIGCHLD, &infop->si_signo);
  	if (!retval && infop)
  		retval = put_user(0, &infop->si_errno);
  	if (!retval && infop)

  		retval = put_user((short)why, &infop->si_code);

  	if (!retval && infop)
  		retval = put_user(exit_code, &infop->si_status);
  	if (!retval && infop)

  		retval = put_user(pid, &infop->si_pid);

  	if (!retval && infop)

  		retval = put_user(uid, &infop->si_uid);

  	if (!retval)

  		retval = pid;

  	put_task_struct(p);
  
  	BUG_ON(!retval);
  	return retval;
  }
  
  /*
   * Handle do_wait work for one task in a live, non-stopped state.
   * read_lock(&tasklist_lock) on entry.  If we return zero, we still hold
   * the lock and this task is uninteresting.  If we return nonzero, we have
   * released the lock and the system call should return.
   */

  static int wait_task_continued(struct wait_opts *wo, struct task_struct *p)

  {
  	int retval;
  	pid_t pid;
  	uid_t uid;

  	if (!unlikely(wo->wo_flags & WCONTINUED))

  		return 0;

  	if (!(p->signal->flags & SIGNAL_STOP_CONTINUED))
  		return 0;
  
  	spin_lock_irq(&p->sighand->siglock);
  	/* Re-check with the lock held.  */
  	if (!(p->signal->flags & SIGNAL_STOP_CONTINUED)) {
  		spin_unlock_irq(&p->sighand->siglock);
  		return 0;
  	}

  	if (!unlikely(wo->wo_flags & WNOWAIT))

  		p->signal->flags &= ~SIGNAL_STOP_CONTINUED;

  	uid = task_uid(p);

  	spin_unlock_irq(&p->sighand->siglock);

  	pid = task_pid_vnr(p);

  	get_task_struct(p);
  	read_unlock(&tasklist_lock);

  	if (!wo->wo_info) {
  		retval = wo->wo_rusage
  			? getrusage(p, RUSAGE_BOTH, wo->wo_rusage) : 0;

  		put_task_struct(p);

  		if (!retval && wo->wo_stat)
  			retval = put_user(0xffff, wo->wo_stat);

  		if (!retval)

  			retval = pid;

  	} else {

  		retval = wait_noreap_copyout(wo, p, pid, uid,
  					     CLD_CONTINUED, SIGCONT);

  		BUG_ON(retval == 0);
  	}
  
  	return retval;
  }

  /*
   * Consider @p for a wait by @parent.
   *

   * -ECHILD should be in ->notask_error before the first call.

   * Returns nonzero for a final return, when we have unlocked tasklist_lock.
   * Returns zero if the search for a child should continue;

   * then ->notask_error is 0 if @p is an eligible child,

   * or another error from security_task_wait(), or still -ECHILD.

   */

  static int wait_consider_task(struct wait_opts *wo, int ptrace,
  				struct task_struct *p)

  {

  	int ret = eligible_child(wo, p);

  	if (!ret)

  		return ret;

  	ret = security_task_wait(p);

  	if (unlikely(ret < 0)) {
  		/*
  		 * If we have not yet seen any eligible child,
  		 * then let this error code replace -ECHILD.
  		 * A permission error will give the user a clue
  		 * to look for security policy problems, rather
  		 * than for mysterious wait bugs.
  		 */

  		if (wo->notask_error)
  			wo->notask_error = ret;

  		return 0;

  	}

  	if (likely(!ptrace) && unlikely(task_ptrace(p))) {

  		/*
  		 * This child is hidden by ptrace.
  		 * We aren't allowed to see it now, but eventually we will.
  		 */

  		wo->notask_error = 0;

  		return 0;
  	}

  	if (p->exit_state == EXIT_DEAD)
  		return 0;
  
  	/*
  	 * We don't reap group leaders with subthreads.
  	 */
  	if (p->exit_state == EXIT_ZOMBIE && !delay_group_leader(p))

  		return wait_task_zombie(wo, p);

  
  	/*
  	 * It's stopped or running now, so it might
  	 * later continue, exit, or stop again.
  	 */

  	wo->notask_error = 0;

  	if (task_stopped_code(p, ptrace))

  		return wait_task_stopped(wo, ptrace, p);

  	return wait_task_continued(wo, p);

  }
  
  /*
   * Do the work of do_wait() for one thread in the group, @tsk.
   *

   * -ECHILD should be in ->notask_error before the first call.

   * Returns nonzero for a final return, when we have unlocked tasklist_lock.
   * Returns zero if the search for a child should continue; then

   * ->notask_error is 0 if there were any eligible children,

   * or another error from security_task_wait(), or still -ECHILD.