text: /*
   *  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/freezer.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/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 <linux/writeback.h>
  #include <linux/shm.h>
  
  #include <asm/uaccess.h>
  #include <asm/unistd.h>
  #include <asm/pgtable.h>
  #include <asm/mmu_context.h>
  
  #ifdef CONFIG_MT_PRIO_TRACER
  # include <linux/prio_tracer.h>
  #endif
  
  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);
  	list_del_rcu(&p->thread_node);
  }
  
  /*
   * 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);
  	cputime_t utime, stime;
  
  	sighand = rcu_dereference_check(tsk->sighand,
  					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.
  		 */
  		task_cputime(tsk, &utime, &stime);
  		sig->utime += utime;
  		sig->stime += stime;
  		sig->gtime += task_gtime(tsk);
  		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:
  	/* 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);
  	ptrace_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) {
  		/*
  		 * 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.
  		 */
  		zap_leader = do_notify_parent(leader, leader->exit_signal);
  		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 bool has_stopped_jobs(struct pid *pgrp)
  {
  	struct task_struct *p;
  
  	do_each_pid_task(pgrp, PIDTYPE_PGID, p) {
  		if (p->signal->flags & SIGNAL_STOP_STOPPED)
  			return true;
  	} while_each_pid_task(pgrp, PIDTYPE_PGID, p);
  
  	return false;
  }
  
  /*
   * 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);
  	}
  }
  
  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);
  }
  
  /*
   * 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);
  
  #ifdef CONFIG_MM_OWNER
  /*
   * A task is exiting.   If it owned this mm, find a new owner for the mm.
   */
  void mm_update_next_owner(struct mm_struct *mm)
  {
  	struct task_struct *c, *g, *p = current;
  
  retry:
  	/*
  	 * If the exiting or execing task is not the owner, it's
  	 * someone else's problem.
  	 */
  	if (mm->owner != p)
  		return;
  	/*
  	 * The current owner is exiting/execing and there are no other
  	 * candidates.  Do not leave the mm pointing to a possibly
  	 * freed task structure.
  	 */
  	if (atomic_read(&mm->mm_users) <= 1) {
  		mm->owner = NULL;
  		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;
  	sync_mm_rss(mm);
  	/*
  	 * 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;
  			freezable_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);
  	task_unlock(tsk);
  	mm_update_next_owner(mm);
  	mmput(mm);
  }
  
  /*
   * When we die, we re-parent all our children, and try to:
   * 1. give them to another thread in our thread group, if such a member exists
   * 2. give it to the first ancestor process which prctl'd itself as a
   *    child_subreaper for its children (like a service manager)
   * 3. give it to the init process (PID 1) in our pid namespace
   */
  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! exitcode=0x%08x\n",
  				father->signal->group_exit_code ?:
  					father->exit_code);
  		}
  
  		zap_pid_ns_processes(pid_ns);
  		write_lock_irq(&tasklist_lock);
  	} else if (father->signal->has_child_subreaper) {
  		struct task_struct *reaper;
  
  		/*
  		 * Find the first ancestor marked as child_subreaper.
  		 * Note that the code below checks same_thread_group(reaper,
  		 * pid_ns->child_reaper).  This is what we need to DTRT in a
  		 * PID namespace. However we still need the check above, see
  		 * http://marc.info/?l=linux-kernel&m=131385460420380
  		 */
  		for (reaper = father->real_parent;
  		     reaper != &init_task;
  		     reaper = reaper->real_parent) {
  			if (same_thread_group(reaper, pid_ns->child_reaper))
  				break;
  			if (!reaper->signal->is_child_subreaper)
  				continue;
  			thread = reaper;
  			do {
  				if (!(thread->flags & PF_EXITING))
  					return reaper;
  			} while_each_thread(reaper, thread);
  		}
  	}
  
  	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 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.
  	 *
  	 * Note: we do this even if it is EXIT_DEAD, wait_task_zombie()
  	 * can change ->exit_state to EXIT_ZOMBIE. If this is the final
  	 * state, do_notify_parent() was already called and ->exit_signal
  	 * doesn't matter.
  	 */
  	p->exit_signal = SIGCHLD;
  
  	if (p->exit_state == EXIT_DEAD)
  		return;
  
  	/* If it has exited notify the new parent about this child's death. */
  	if (!p->ptrace &&
  	    p->exit_state == EXIT_ZOMBIE && thread_group_empty(p)) {
  		if (do_notify_parent(p, p->exit_signal)) {
  			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(t->ptrace);
  				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)
  {
  	bool autoreap;
  
  	/*
  	 * 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);
  
  	write_lock_irq(&tasklist_lock);
  	if (group_dead)
  		kill_orphaned_pgrp(tsk->group_leader, NULL);
  
  	if (unlikely(tsk->ptrace)) {
  		int sig = thread_group_leader(tsk) &&
  				thread_group_empty(tsk) &&
  				!ptrace_reparented(tsk) ?
  			tsk->exit_signal : SIGCHLD;
  		autoreap = do_notify_parent(tsk, sig);
  	} else if (thread_group_leader(tsk)) {
  		autoreap = thread_group_empty(tsk) &&
  			do_notify_parent(tsk, tsk->exit_signal);
  	} else {
  		autoreap = true;
  	}
  
  	tsk->exit_state = autoreap ? 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);
  
  	/* If the process is dead, release it - nobody will wait for it */
  	if (autoreap)
  		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 (%d) used greatest stack depth: "
  				"%lu bytes left\n",
  				current->comm, task_pid_nr(current), free);
  		lowest_to_date = free;
  	}
  	spin_unlock(&low_water_lock);
  }
  #else
  static inline void check_stack_usage(void) {}
  #endif
  
  #ifdef CONFIG_SCHEDSTATS
  /* mt shceduler profiling*/
  extern void end_mtproc_info(struct task_struct *p);
  #endif
  void do_exit(long code)
  {
  	struct task_struct *tsk = current;
  	int group_dead;
  
  	profile_task_exit(tsk);
  #ifdef CONFIG_SCHEDSTATS
  	/* mt shceduler profiling*/
  	printk(KERN_DEBUG "[%d:%s] exit\n", tsk->pid, tsk->comm);
  	end_mtproc_info(tsk);
  #endif
  
  #ifdef CONFIG_MT_PRIO_TRACER
  	delete_prio_tracer(tsk->pid);
  #endif
  
  	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);
  
  	ptrace_event(PTRACE_EVENT_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!\n");
  		/*
  		 * 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_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\n",
  				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->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();
  	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_shm(tsk);
  	exit_files(tsk);
  	exit_fs(tsk);
  	if (group_dead)
  		disassociate_ctty(1);
  	exit_task_namespaces(tsk);
  	exit_task_work(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);
  
  	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();
  	/*
  	 * 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);
  
  	if (tsk->task_frag.page)
  		put_page(tsk->task_frag.page);
  
  	validate_creds_for_do_exit(tsk);
  
  	preempt_disable();
  	if (tsk->nr_dirtied)
  		__this_cpu_add(dirty_throttle_leaks, tsk->nr_dirtied);
  	exit_rcu();
  
  	/*
  	 * The setting of TASK_RUNNING by try_to_wake_up() may be delayed
  	 * when the following two conditions become true.
  	 *   - There is race condition of mmap_sem (It is acquired by
  	 *     exit_mm()), and
  	 *   - SMI occurs before setting TASK_RUNINNG.
  	 *     (or hypervisor of virtual machine switches to other guest)
  	 *  As a result, we may become TASK_RUNNING after becoming TASK_DEAD
  	 *
  	 * To avoid it, we have to wait for releasing tsk->pi_lock which
  	 * is held by try_to_wake_up()
  	 */
  	smp_mb();
  	raw_spin_unlock_wait(&tsk->pi_lock);
  
  	/* causes final put_task_struct in finish_task_switch(). */
  	tsk->state = TASK_DEAD;
  	tsk->flags |= PF_NOFREEZE;	/* tell freezer to ignore us */
  	schedule();
  	BUG();
  	/* Avoid "noreturn function does return".  */
  	for (;;)
  		cpu_relax();	/* For when BUG is null */
  }
  
  EXPORT_SYMBOL_GPL(do_exit);
  
  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).
   */
  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 = from_kuid_munged(current_user_ns(), task_uid(p));
  	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
  	 * thread_group_leader() to filter out sub-threads.
  	 */
  	if (likely(!traced) && thread_group_leader(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_cputime_adjusted() to get times for the thread
  		 * group, which consolidates times for all threads in the
  		 * group including the group leader.
  		 */
  		thread_group_cputime_adjusted(p, &tgutime, &tgstime);
  		spin_lock_irq(&p->real_parent->sighand->siglock);
  		psig = p->real_parent->signal;
  		sig = p->signal;
  		psig->cutime += tgutime + sig->cutime;
  		psig->cstime += tgstime + sig->cstime;
  		psig->cgtime += task_gtime(p) + 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 sub-thread, notify the parent.
  		 * If parent wants a zombie, don't release it now.
  		 */
  		if (thread_group_leader(p) &&
  		    !do_notify_parent(p, p->exit_signal)) {
  			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) &&
  		    !(p->jobctl & JOBCTL_LISTENING))
  			return &p->exit_code;
  	} else {
  		if (p->signal->flags & SIGNAL_STOP_STOPPED)
  			return &p->signal->group_exit_code;
  	}
  	return NULL;
  }
  
  /**
   * wait_task_stopped - Wait for %TASK_STOPPED or %TASK_TRACED
   * @wo: wait options
   * @ptrace: is the wait for ptrace
   * @p: task to wait for
   *
   * Handle sys_wait4() work for %p in state %TASK_STOPPED or %TASK_TRACED.
   *
   * CONTEXT:
   * read_lock(&tasklist_lock), which is released if return value is
   * non-zero.  Also, grabs and releases @p->sighand->siglock.
   *
   * RETURNS:
   * 0 if wait condition didn't exist and search for other wait conditions
   * should continue.  Non-zero return, -errno on failure and @p's pid on
   * success, implies that tasklist_lock is released and wait condition
   * search should terminate.
   */
  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;
  
  	if (!task_stopped_code(p, ptrace))
  		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 = from_kuid_munged(current_user_ns(), 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 = from_kuid_munged(current_user_ns(), 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;
  	}
  
  	/* dead body doesn't have much to contribute */
  	if (unlikely(p->exit_state == EXIT_DEAD)) {
  		/*
  		 * But do not ignore this task until the tracer does
  		 * wait_task_zombie()->do_notify_parent().
  		 */
  		if (likely(!ptrace) && unlikely(ptrace_reparented(p)))
  			wo->notask_error = 0;
  		return 0;
  	}
  
  	/* slay zombie? */
  	if (p->exit_state == EXIT_ZOMBIE) {
  		/*
  		 * A zombie ptracee is only visible to its ptracer.
  		 * Notification and reaping will be cascaded to the real
  		 * parent when the ptracer detaches.
  		 */
  		if (likely(!ptrace) && unlikely(p->ptrace)) {
  			/* it will become visible, clear notask_error */
  			wo->notask_error = 0;
  			return 0;
  		}
  
  		/* we don't reap group leaders with subthreads */
  		if (!delay_group_leader(p))
  			return wait_task_zombie(wo, p);
  
  		/*
  		 * Allow access to stopped/continued state via zombie by
  		 * falling through.  Clearing of notask_error is complex.
  		 *
  		 * When !@ptrace:
  		 *
  		 * If WEXITED is set, notask_error should naturally be
  		 * cleared.  If not, subset of WSTOPPED|WCONTINUED is set,
  		 * so, if there are live subthreads, there are events to
  		 * wait for.  If all subthreads are dead, it's still safe
  		 * to clear - this function will be called again in finite
  		 * amount time once all the subthreads are released and
  		 * will then return without clearing.
  		 *
  		 * When @ptrace:
  		 *
  		 * Stopped state is per-task and thus can't change once the
  		 * target task dies.  Only continued and exited can happen.
  		 * Clear notask_error if WCONTINUED | WEXITED.
  		 */
  		if (likely(!ptrace) || (wo->wo_flags & (WCONTINUED | WEXITED)))
  			wo->notask_error = 0;
  	} else {
  		/*
  		 * If @p is ptraced by a task in its real parent's group,
  		 * hide group stop/continued state when looking at @p as
  		 * the real parent; otherwise, a single stop can be
  		 * reported twice as group and ptrace stops.
  		 *
  		 * If a ptracer wants to distinguish the two events for its
  		 * own children, it should create a separate process which
  		 * takes the role of real parent.
  		 */
  		if (likely(!ptrace) && p->ptrace && !ptrace_reparented(p))
  			return 0;
  
  		/*
  		 * @p is alive and it's gonna stop, continue or exit, so
  		 * there always is something to wait for.
  		 */
  		wo->notask_error = 0;
  	}
  
  	/*
  	 * Wait for stopped.  Depending on @ptrace, different stopped state
  	 * is used and the two don't interact with each other.
  	 */
  	ret = wait_task_stopped(wo, ptrace, p);
  	if (ret)
  		return ret;
  
  	/*
  	 * Wait for continued.  There's only one continued state and the
  	 * ptracer can consume it which can confuse the real parent.  Don't
  	 * use WCONTINUED from ptracer.  You don't need or want it.
  	 */
  	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.
   */
  static int do_wait_thread(struct wait_opts *wo, struct task_struct *tsk)
  {
  	struct task_struct *p;
  
  	list_for_each_entry(p, &tsk->children, sibling) {
  		int ret = wait_consider_task(wo, 0, p);
  		if (ret)
  			return ret;
  	}
  
  	return 0;
  }
  
  static int ptrace_do_wait(struct wait_opts *wo, struct task_struct *tsk)
  {
  	struct task_struct *p;
  
  	list_for_each_entry(p, &tsk->ptraced, ptrace_entry) {
  		int ret = wait_consider_task(wo, 1, p);
  		if (ret)
  			return ret;
  	}
  
  	return 0;
  }
  
  static int child_wait_callback(wait_queue_t *wait, unsigned mode,
  				int sync, void *key)
  {
  	struct wait_opts *wo = container_of(wait, struct wait_opts,
  						child_wait);
  	struct task_struct *p = key;
  
  	if (!eligible_pid(wo, p))
  		return 0;
  
  	if ((wo->wo_flags & __WNOTHREAD) && wait->private != p->parent)
  		return 0;
  
  	return default_wake_function(wait, mode, sync, key);
  }
  
  void __wake_up_parent(struct task_struct *p, struct task_struct *parent)
  {
  	__wake_up_sync_key(&parent->signal->wait_chldexit,
  				TASK_INTERRUPTIBLE, 1, p);
  }
  
  static long do_wait(struct wait_opts *wo)
  {
  	struct task_struct *tsk;
  	int retval;
  
  	trace_sched_process_wait(wo->wo_pid);
  
  	init_waitqueue_func_entry(&wo->child_wait, child_wait_callback);
  	wo->child_wait.private = current;
  	add_wait_queue(&current->signal->wait_chldexit, &wo->child_wait);
  repeat:
  	/*
  	 * If there is nothing that can match our critiera just get out.
  	 * We will clear ->notask_error to zero if we see any child that
  	 * might later match our criteria, even if we are not able to reap
  	 * it yet.
  	 */
  	wo->notask_error = -ECHILD;
  	if ((wo->wo_type < PIDTYPE_MAX) &&
  	   (!wo->wo_pid || hlist_empty(&wo->wo_pid->tasks[wo->wo_type])))
  		goto notask;
  
  	set_current_state(TASK_INTERRUPTIBLE);
  	read_lock(&tasklist_lock);
  	tsk = current;
  	do {
  		retval = do_wait_thread(wo, tsk);
  		if (retval)
  			goto end;
  
  		retval = ptrace_do_wait(wo, tsk);
  		if (retval)
  			goto end;
  
  		if (wo->wo_flags & __WNOTHREAD)
  			break;
  	} while_each_thread(current, tsk);
  	read_unlock(&tasklist_lock);
  
  notask:
  	retval = wo->notask_error;
  	if (!retval && !(wo->wo_flags & WNOHANG)) {
  		retval = -ERESTARTSYS;
  		if (!signal_pending(current)) {
  			schedule();
  			goto repeat;
  		}
  	}
  end:
  	__set_current_state(TASK_RUNNING);
  	remove_wait_queue(&current->signal->wait_chldexit, &wo->child_wait);
  	return retval;
  }
  
  SYSCALL_DEFINE5(waitid, int, which, pid_t, upid, struct siginfo __user *,
  		infop, int, options, struct rusage __user *, ru)
  {
  	struct wait_opts wo;
  	struct pid *pid = NULL;
  	enum pid_type type;
  	long ret;
  
  	if (options & ~(WNOHANG|WNOWAIT|WEXITED|WSTOPPED|WCONTINUED))
  		return -EINVAL;
  	if (!(options & (WEXITED|WSTOPPED|WCONTINUED)))
  		return -EINVAL;
  
  	switch (which) {
  	case P_ALL:
  		type = PIDTYPE_MAX;
  		break;
  	case P_PID:
  		type = PIDTYPE_PID;
  		if (upid <= 0)
  			return -EINVAL;
  		break;
  	case P_PGID:
  		type = PIDTYPE_PGID;
  		if (upid <= 0)
  			return -EINVAL;
  		break;
  	default:
  		return -EINVAL;
  	}
  
  	if (type < PIDTYPE_MAX)
  		pid = find_get_pid(upid);
  
  	wo.wo_type	= type;
  	wo.wo_pid	= pid;
  	wo.wo_flags	= options;
  	wo.wo_info	= infop;
  	wo.wo_stat	= NULL;
  	wo.wo_rusage	= ru;
  	ret = do_wait(&wo);
  
  	if (ret > 0) {
  		ret = 0;
  	} else if (infop) {
  		/*
  		 * For a WNOHANG return, clear out all the fields
  		 * we would set so the user can easily tell the
  		 * difference.
  		 */
  		if (!ret)
  			ret = put_user(0, &infop->si_signo);
  		if (!ret)
  			ret = put_user(0, &infop->si_errno);
  		if (!ret)
  			ret = put_user(0, &infop->si_code);
  		if (!ret)
  			ret = put_user(0, &infop->si_pid);
  		if (!ret)
  			ret = put_user(0, &infop->si_uid);
  		if (!ret)
  			ret = put_user(0, &infop->si_status);
  	}
  
  	put_pid(pid);
  	return ret;
  }
  
  SYSCALL_DEFINE4(wait4, pid_t, upid, int __user *, stat_addr,
  		int, options, struct rusage __user *, ru)
  {
  	struct wait_opts wo;
  	struct pid *pid = NULL;
  	enum pid_type type;
  	long ret;
  
  	if (options & ~(WNOHANG|WUNTRACED|WCONTINUED|
  			__WNOTHREAD|__WCLONE|__WALL))
  		return -EINVAL;
  
  	if (upid == -1)
  		type = PIDTYPE_MAX;
  	else if (upid < 0) {
  		type = PIDTYPE_PGID;
  		pid = find_get_pid(-upid);
  	} else if (upid == 0) {
  		type = PIDTYPE_PGID;
  		pid = get_task_pid(current, PIDTYPE_PGID);
  	} else /* upid > 0 */ {
  		type = PIDTYPE_PID;
  		pid = find_get_pid(upid);
  	}
  
  	wo.wo_type	= type;
  	wo.wo_pid	= pid;
  	wo.wo_flags	= options | WEXITED;
  	wo.wo_info	= NULL;
  	wo.wo_stat	= stat_addr;
  	wo.wo_rusage	= ru;
  	ret = do_wait(&wo);
  	put_pid(pid);
  
  	return ret;
  }
  
  #ifdef __ARCH_WANT_SYS_WAITPID
  
  /*
   * sys_waitpid() remains for compatibility. waitpid() should be
   * implemented by calling sys_wait4() from libc.a.
   */
  SYSCALL_DEFINE3(waitpid, pid_t, pid, int __user *, stat_addr, int, options)
  {
  	return sys_wait4(pid, stat_addr, options, NULL);
  }
  
  #endif
  