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33 results

exit.c

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  • exit.c 44.05 KiB
    /*
     *  linux/kernel/exit.c
     *
     *  Copyright (C) 1991, 1992  Linus Torvalds
     */
    
    #include <linux/mm.h>
    #include <linux/slab.h>
    #include <linux/sched/autogroup.h>
    #include <linux/sched/mm.h>
    #include <linux/sched/stat.h>
    #include <linux/sched/task.h>
    #include <linux/sched/task_stack.h>
    #include <linux/sched/cputime.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/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 <linux/kcov.h>
    #include <linux/random.h>
    #include <linux/rcuwait.h>
    #include <linux/compat.h>
    
    #include <linux/uaccess.h>
    #include <asm/unistd.h>
    #include <asm/pgtable.h>
    #include <asm/mmu_context.h>
    
    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);
    	u64 utime, stime;
    
    	sighand = rcu_dereference_check(tsk->sighand,
    					lockdep_tasklist_lock_is_held());
    	spin_lock(&sighand->siglock);
    
    #ifdef CONFIG_POSIX_TIMERS
    	posix_cpu_timers_exit(tsk);
    	if (group_dead) {
    		posix_cpu_timers_exit_group(tsk);
    	} 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);
    	}
    #endif
    
    	if (group_dead) {
    		tty = sig->tty;
    		sig->tty = NULL;
    	} else {
    		/*
    		 * 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);
    	}
    
    	add_device_randomness((const void*) &tsk->se.sum_exec_runtime,
    			      sizeof(unsigned long long));
    
    	/*
    	 * Accumulate here the counters for all threads as they die. We could
    	 * skip the group leader because it is the last user of signal_struct,
    	 * but we want to avoid the race with thread_group_cputime() which can
    	 * see the empty ->thread_head list.
    	 */
    	task_cputime(tsk, &utime, &stime);
    	write_seqlock(&sig->stats_lock);
    	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);
    	write_sequnlock(&sig->stats_lock);
    
    	/*
    	 * 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;
    }
    
    /*
     * Note that if this function returns a valid task_struct pointer (!NULL)
     * task->usage must remain >0 for the duration of the RCU critical section.
     */
    struct task_struct *task_rcu_dereference(struct task_struct **ptask)
    {
    	struct sighand_struct *sighand;
    	struct task_struct *task;
    
    	/*
    	 * We need to verify that release_task() was not called and thus
    	 * delayed_put_task_struct() can't run and drop the last reference
    	 * before rcu_read_unlock(). We check task->sighand != NULL,
    	 * but we can read the already freed and reused memory.
    	 */
    retry:
    	task = rcu_dereference(*ptask);
    	if (!task)
    		return NULL;
    
    	probe_kernel_address(&task->sighand, sighand);
    
    	/*
    	 * Pairs with atomic_dec_and_test() in put_task_struct(). If this task
    	 * was already freed we can not miss the preceding update of this
    	 * pointer.
    	 */
    	smp_rmb();
    	if (unlikely(task != READ_ONCE(*ptask)))
    		goto retry;
    
    	/*
    	 * We've re-checked that "task == *ptask", now we have two different
    	 * cases:
    	 *
    	 * 1. This is actually the same task/task_struct. In this case
    	 *    sighand != NULL tells us it is still alive.
    	 *
    	 * 2. This is another task which got the same memory for task_struct.
    	 *    We can't know this of course, and we can not trust
    	 *    sighand != NULL.
    	 *
    	 *    In this case we actually return a random value, but this is
    	 *    correct.
    	 *
    	 *    If we return NULL - we can pretend that we actually noticed that
    	 *    *ptask was updated when the previous task has exited. Or pretend
    	 *    that probe_slab_address(&sighand) reads NULL.
    	 *
    	 *    If we return the new task (because sighand is not NULL for any
    	 *    reason) - this is fine too. This (new) task can't go away before
    	 *    another gp pass.
    	 *
    	 *    And note: We could even eliminate the false positive if re-read
    	 *    task->sighand once again to avoid the falsely NULL. But this case
    	 *    is very unlikely so we don't care.
    	 */
    	if (!sighand)
    		return NULL;
    
    	return task;
    }
    
    void rcuwait_wake_up(struct rcuwait *w)
    {
    	struct task_struct *task;
    
    	rcu_read_lock();
    
    	/*
    	 * Order condition vs @task, such that everything prior to the load
    	 * of @task is visible. This is the condition as to why the user called
    	 * rcuwait_trywake() in the first place. Pairs with set_current_state()
    	 * barrier (A) in rcuwait_wait_event().
    	 *
    	 *    WAIT                WAKE
    	 *    [S] tsk = current	  [S] cond = true
    	 *        MB (A)	      MB (B)
    	 *    [L] cond		  [L] tsk
    	 */
    	smp_rmb(); /* (B) */
    
    	/*
    	 * Avoid using task_rcu_dereference() magic as long as we are careful,
    	 * see comment in rcuwait_wait_event() regarding ->exit_state.
    	 */
    	task = rcu_dereference(w->task);
    	if (task)
    		wake_up_process(task);
    	rcu_read_unlock();
    }
    
    /*
     * 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);
    	}
    }
    
    #ifdef CONFIG_MEMCG
    /*
     * 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.
    	 */
    	for_each_process(g) {
    		if (g->flags & PF_KTHREAD)
    			continue;
    		for_each_thread(g, c) {
    			if (c->mm == mm)
    				goto assign_new_owner;
    			if (c->mm)
    				break;
    		}
    	}
    	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_MEMCG */
    
    /*
     * Turn us into a lazy TLB process if we
     * aren't already..
     */
    static void exit_mm(void)
    {
    	struct mm_struct *mm = current->mm;
    	struct core_state *core_state;
    
    	mm_release(current, 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 = current;
    		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_current_state(TASK_UNINTERRUPTIBLE);
    			if (!self.task) /* see coredump_finish() */
    				break;
    			freezable_schedule();
    		}
    		__set_current_state(TASK_RUNNING);
    		down_read(&mm->mmap_sem);
    	}
    	mmgrab(mm);
    	BUG_ON(mm != current->active_mm);
    	/* more a memory barrier than a real lock */
    	task_lock(current);
    	current->mm = NULL;
    	up_read(&mm->mmap_sem);
    	enter_lazy_tlb(mm, current);
    	task_unlock(current);
    	mm_update_next_owner(mm);
    	mmput(mm);
    	if (test_thread_flag(TIF_MEMDIE))
    		exit_oom_victim();
    }
    
    static struct task_struct *find_alive_thread(struct task_struct *p)
    {
    	struct task_struct *t;
    
    	for_each_thread(p, t) {
    		if (!(t->flags & PF_EXITING))
    			return t;
    	}
    	return NULL;
    }
    
    static struct task_struct *find_child_reaper(struct task_struct *father)
    	__releases(&tasklist_lock)
    	__acquires(&tasklist_lock)
    {
    	struct pid_namespace *pid_ns = task_active_pid_ns(father);
    	struct task_struct *reaper = pid_ns->child_reaper;
    
    	if (likely(reaper != father))
    		return reaper;
    
    	reaper = find_alive_thread(father);
    	if (reaper) {
    		pid_ns->child_reaper = reaper;
    		return reaper;
    	}
    
    	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);
    
    	return father;
    }
    
    /*
     * 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,
    					   struct task_struct *child_reaper)
    {
    	struct task_struct *thread, *reaper;
    
    	thread = find_alive_thread(father);
    	if (thread)
    		return thread;
    
    	if (father->signal->has_child_subreaper) {
    		unsigned int ns_level = task_pid(father)->level;
    		/*
    		 * Find the first ->is_child_subreaper ancestor in our pid_ns.
    		 * We can't check reaper != child_reaper to ensure we do not
    		 * cross the namespaces, the exiting parent could be injected
    		 * by setns() + fork().
    		 * We check pid->level, this is slightly more efficient than
    		 * task_active_pid_ns(reaper) != task_active_pid_ns(father).
    		 */
    		for (reaper = father->real_parent;
    		     task_pid(reaper)->level == ns_level;
    		     reaper = reaper->real_parent) {
    			if (reaper == &init_task)
    				break;
    			if (!reaper->signal->is_child_subreaper)
    				continue;
    			thread = find_alive_thread(reaper);
    			if (thread)
    				return thread;
    		}
    	}
    
    	return 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)
    {
    	if (unlikely(p->exit_state == EXIT_DEAD))
    		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 (!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_add(&p->ptrace_entry, dead);
    		}
    	}
    
    	kill_orphaned_pgrp(p, father);
    }
    
    /*
     * 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)
     */
    static void forget_original_parent(struct task_struct *father,
    					struct list_head *dead)
    {
    	struct task_struct *p, *t, *reaper;
    
    	if (unlikely(!list_empty(&father->ptraced)))
    		exit_ptrace(father, dead);
    
    	/* Can drop and reacquire tasklist_lock */
    	reaper = find_child_reaper(father);
    	if (list_empty(&father->children))
    		return;
    
    	reaper = find_new_reaper(father, reaper);
    	list_for_each_entry(p, &father->children, sibling) {
    		for_each_thread(p, t) {
    			t->real_parent = reaper;
    			BUG_ON((!t->ptrace) != (t->parent == father));
    			if (likely(!t->ptrace))
    				t->parent = t->real_parent;
    			if (t->pdeath_signal)
    				group_send_sig_info(t->pdeath_signal,
    						    SEND_SIG_NOINFO, t);
    		}
    		/*
    		 * If this is a threaded reparent there is no need to
    		 * notify anyone anything has happened.
    		 */
    		if (!same_thread_group(reaper, father))
    			reparent_leader(father, p, dead);
    	}
    	list_splice_tail_init(&father->children, &reaper->children);
    }
    
    /*
     * 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;
    	struct task_struct *p, *n;
    	LIST_HEAD(dead);
    
    	write_lock_irq(&tasklist_lock);
    	forget_original_parent(tsk, &dead);
    
    	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;
    	if (tsk->exit_state == EXIT_DEAD)
    		list_add(&tsk->ptrace_entry, &dead);
    
    	/* 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);
    
    	list_for_each_entry_safe(p, n, &dead, ptrace_entry) {
    		list_del_init(&p->ptrace_entry);
    		release_task(p);
    	}
    }
    
    #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) {
    		pr_info("%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
    
    void __noreturn do_exit(long code)
    {
    	struct task_struct *tsk = current;
    	int group_dead;
    
    	profile_task_exit(tsk);
    	kcov_task_exit(tsk);
    
    	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)) {
    		pr_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 */
    	/*
    	 * Ensure that all new tsk->pi_lock acquisitions must observe
    	 * PF_EXITING. Serializes against futex.c:attach_to_pi_owner().
    	 */
    	smp_mb();
    	/*
    	 * Ensure that we must observe the pi_state in exit_mm() ->
    	 * mm_release() -> exit_pi_state_list().
    	 */
    	raw_spin_lock_irq(&tsk->pi_lock);
    	raw_spin_unlock_irq(&tsk->pi_lock);
    
    	if (unlikely(in_atomic())) {
    		pr_info("note: %s[%d] exited with preempt_count %d\n",
    			current->comm, task_pid_nr(current),
    			preempt_count());
    		preempt_count_set(PREEMPT_ENABLED);
    	}
    
    	/* sync mm's RSS info before statistics gathering */
    	if (tsk->mm)
    		sync_mm_rss(tsk->mm);
    	acct_update_integrals(tsk);
    	group_dead = atomic_dec_and_test(&tsk->signal->live);
    	if (group_dead) {
    #ifdef CONFIG_POSIX_TIMERS
    		hrtimer_cancel(&tsk->signal->real_timer);
    		exit_itimers(tsk->signal);
    #endif
    		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();
    
    	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);
    	exit_thread(tsk);
    
    	/*
    	 * 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);
    
    	sched_autogroup_exit_task(tsk);
    	cgroup_exit(tsk);
    
    	/*
    	 * FIXME: do that only when needed, using sched_exit tracepoint
    	 */
    	flush_ptrace_hw_breakpoint(tsk);
    
    	exit_tasks_rcu_start();
    	exit_notify(tsk, group_dead);
    	proc_exit_connector(tsk);
    	mpol_put_task_policy(tsk);
    #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);
    
    	check_stack_usage();
    	preempt_disable();
    	if (tsk->nr_dirtied)
    		__this_cpu_add(dirty_throttle_leaks, tsk->nr_dirtied);
    	exit_rcu();
    	exit_tasks_rcu_finish();
    
    	lockdep_free_task(tsk);
    	do_task_dead();
    }
    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 waitid_info {
    	pid_t pid;
    	uid_t uid;
    	int status;
    	int cause;
    };
    
    struct wait_opts {
    	enum pid_type		wo_type;
    	int			wo_flags;
    	struct pid		*wo_pid;
    
    	struct waitid_info	*wo_info;
    	int			wo_stat;
    	struct rusage		*wo_rusage;
    
    	wait_queue_entry_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, bool ptrace, struct task_struct *p)
    {
    	if (!eligible_pid(wo, p))
    		return 0;
    
    	/*
    	 * Wait for all children (clone and not) if __WALL is set or
    	 * if it is traced by us.
    	 */
    	if (ptrace || (wo->wo_flags & __WALL))
    		return 1;
    
    	/*
    	 * 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, or a non-leader thread which
    	 * we can only see if it is traced by us.
    	 */
    	if ((p->exit_signal != SIGCHLD) ^ !!(wo->wo_flags & __WCLONE))
    		return 0;
    
    	return 1;
    }
    
    /*
     * 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)
    {
    	int state, status;
    	pid_t pid = task_pid_vnr(p);
    	uid_t uid = from_kuid_munged(current_user_ns(), task_uid(p));
    	struct waitid_info *infop;
    
    	if (!likely(wo->wo_flags & WEXITED))
    		return 0;
    
    	if (unlikely(wo->wo_flags & WNOWAIT)) {
    		status = p->exit_code;
    		get_task_struct(p);
    		read_unlock(&tasklist_lock);
    		sched_annotate_sleep();
    		if (wo->wo_rusage)
    			getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
    		put_task_struct(p);
    		goto out_info;
    	}
    	/*
    	 * Move the task's state to DEAD/TRACE, only one thread can do this.
    	 */
    	state = (ptrace_reparented(p) && thread_group_leader(p)) ?
    		EXIT_TRACE : EXIT_DEAD;
    	if (cmpxchg(&p->exit_state, EXIT_ZOMBIE, state) != EXIT_ZOMBIE)
    		return 0;
    	/*
    	 * We own this thread, nobody else can reap it.
    	 */
    	read_unlock(&tasklist_lock);
    	sched_annotate_sleep();
    
    	/*
    	 * Check thread_group_leader() to exclude the traced sub-threads.
    	 */
    	if (state == EXIT_DEAD && thread_group_leader(p)) {
    		struct signal_struct *sig = p->signal;
    		struct signal_struct *psig = current->signal;
    		unsigned long maxrss;
    		u64 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 the whole thread group is dead
    		 * and nobody can change them.
    		 *
    		 * psig->stats_lock also protects us from our sub-theads
    		 * which can reap other children at the same time. Until
    		 * we change k_getrusage()-like users to rely on this lock
    		 * we have to take ->siglock as well.
    		 *
    		 * 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(&current->sighand->siglock);
    		write_seqlock(&psig->stats_lock);
    		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);
    		write_sequnlock(&psig->stats_lock);
    		spin_unlock_irq(&current->sighand->siglock);
    	}
    
    	if (wo->wo_rusage)
    		getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
    	status = (p->signal->flags & SIGNAL_GROUP_EXIT)
    		? p->signal->group_exit_code : p->exit_code;
    	wo->wo_stat = status;
    
    	if (state == EXIT_TRACE) {
    		write_lock_irq(&tasklist_lock);
    		/* We dropped tasklist, ptracer could die and untrace */
    		ptrace_unlink(p);
    
    		/* If parent wants a zombie, don't release it now */
    		state = EXIT_ZOMBIE;
    		if (do_notify_parent(p, p->exit_signal))
    			state = EXIT_DEAD;
    		p->exit_state = state;
    		write_unlock_irq(&tasklist_lock);
    	}
    	if (state == EXIT_DEAD)
    		release_task(p);
    
    out_info:
    	infop = wo->wo_info;
    	if (infop) {
    		if ((status & 0x7f) == 0) {
    			infop->cause = CLD_EXITED;
    			infop->status = status >> 8;
    		} else {
    			infop->cause = (status & 0x80) ? CLD_DUMPED : CLD_KILLED;
    			infop->status = status & 0x7f;
    		}
    		infop->pid = pid;
    		infop->uid = uid;
    	}
    
    	return pid;
    }
    
    static int *task_stopped_code(struct task_struct *p, bool ptrace)
    {
    	if (ptrace) {
    		if (task_is_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 waitid_info *infop;
    	int 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);
    	sched_annotate_sleep();
    	if (wo->wo_rusage)
    		getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
    	put_task_struct(p);
    
    	if (likely(!(wo->wo_flags & WNOWAIT)))
    		wo->wo_stat = (exit_code << 8) | 0x7f;
    
    	infop = wo->wo_info;
    	if (infop) {
    		infop->cause = why;
    		infop->status = exit_code;
    		infop->pid = pid;
    		infop->uid = uid;
    	}
    	return pid;
    }
    
    /*
     * 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)
    {
    	struct waitid_info *infop;
    	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);
    	sched_annotate_sleep();
    	if (wo->wo_rusage)
    		getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
    	put_task_struct(p);
    
    	infop = wo->wo_info;
    	if (!infop) {
    		wo->wo_stat = 0xffff;
    	} else {
    		infop->cause = CLD_CONTINUED;
    		infop->pid = pid;
    		infop->uid = uid;
    		infop->status = SIGCONT;
    	}
    	return pid;
    }
    
    /*
     * 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 still -ECHILD.
     */
    static int wait_consider_task(struct wait_opts *wo, int ptrace,
    				struct task_struct *p)
    {
    	/*
    	 * We can race with wait_task_zombie() from another thread.
    	 * Ensure that EXIT_ZOMBIE -> EXIT_DEAD/EXIT_TRACE transition
    	 * can't confuse the checks below.
    	 */
    	int exit_state = ACCESS_ONCE(p->exit_state);
    	int ret;
    
    	if (unlikely(exit_state == EXIT_DEAD))
    		return 0;
    
    	ret = eligible_child(wo, ptrace, p);
    	if (!ret)
    		return ret;
    
    	if (unlikely(exit_state == EXIT_TRACE)) {
    		/*
    		 * ptrace == 0 means we are the natural parent. In this case
    		 * we should clear notask_error, debugger will notify us.
    		 */
    		if (likely(!ptrace))
    			wo->notask_error = 0;
    		return 0;
    	}
    
    	if (likely(!ptrace) && unlikely(p->ptrace)) {
    		/*
    		 * If it is traced by its real parent's group, just pretend
    		 * the caller is ptrace_do_wait() and reap this child if it
    		 * is zombie.
    		 *
    		 * This also hides group stop state from real parent; otherwise
    		 * a single stop can be reported twice as group and ptrace stop.
    		 * If a ptracer wants to distinguish these two events for its
    		 * own children it should create a separate process which takes
    		 * the role of real parent.
    		 */
    		if (!ptrace_reparented(p))
    			ptrace = 1;
    	}
    
    	/* slay zombie? */
    	if (exit_state == EXIT_ZOMBIE) {
    		/* we don't reap group leaders with subthreads */
    		if (!delay_group_leader(p)) {
    			/*
    			 * A zombie ptracee is only visible to its ptracer.
    			 * Notification and reaping will be cascaded to the
    			 * real parent when the ptracer detaches.
    			 */
    			if (unlikely(ptrace) || likely(!p->ptrace))
    				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 {
    		/*
    		 * @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 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_entry_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 criteria, 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;
    }
    
    static long kernel_waitid(int which, pid_t upid, struct waitid_info *infop,
    			  int options, struct rusage *ru)
    {
    	struct wait_opts wo;
    	struct pid *pid = NULL;
    	enum pid_type type;
    	long ret;
    
    	if (options & ~(WNOHANG|WNOWAIT|WEXITED|WSTOPPED|WCONTINUED|
    			__WNOTHREAD|__WCLONE|__WALL))
    		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_rusage	= ru;
    	ret = do_wait(&wo);
    
    	put_pid(pid);
    	return ret;
    }
    
    SYSCALL_DEFINE5(waitid, int, which, pid_t, upid, struct siginfo __user *,
    		infop, int, options, struct rusage __user *, ru)
    {
    	struct rusage r;
    	struct waitid_info info = {.status = 0};
    	long err = kernel_waitid(which, upid, &info, options, ru ? &r : NULL);
    	int signo = 0;
    
    	if (err > 0) {
    		signo = SIGCHLD;
    		err = 0;
    		if (ru && copy_to_user(ru, &r, sizeof(struct rusage)))
    			return -EFAULT;
    	}
    	if (!infop)
    		return err;
    
    	user_access_begin();
    	unsafe_put_user(signo, &infop->si_signo, Efault);
    	unsafe_put_user(0, &infop->si_errno, Efault);
    	unsafe_put_user(info.cause, &infop->si_code, Efault);
    	unsafe_put_user(info.pid, &infop->si_pid, Efault);
    	unsafe_put_user(info.uid, &infop->si_uid, Efault);
    	unsafe_put_user(info.status, &infop->si_status, Efault);
    	user_access_end();
    	return err;
    Efault:
    	user_access_end();
    	return -EFAULT;
    }
    
    long kernel_wait4(pid_t upid, int __user *stat_addr, int options,
    		  struct rusage *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;
    
    	/* -INT_MIN is not defined */
    	if (upid == INT_MIN)
    		return -ESRCH;
    
    	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	= 0;
    	wo.wo_rusage	= ru;
    	ret = do_wait(&wo);
    	put_pid(pid);
    	if (ret > 0 && stat_addr && put_user(wo.wo_stat, stat_addr))
    		ret = -EFAULT;
    
    	return ret;
    }
    
    SYSCALL_DEFINE4(wait4, pid_t, upid, int __user *, stat_addr,
    		int, options, struct rusage __user *, ru)
    {
    	struct rusage r;
    	long err = kernel_wait4(upid, stat_addr, options, ru ? &r : NULL);
    
    	if (err > 0) {
    		if (ru && copy_to_user(ru, &r, sizeof(struct rusage)))
    			return -EFAULT;
    	}
    	return err;
    }
    
    #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
    
    #ifdef CONFIG_COMPAT
    COMPAT_SYSCALL_DEFINE4(wait4,
    	compat_pid_t, pid,
    	compat_uint_t __user *, stat_addr,
    	int, options,
    	struct compat_rusage __user *, ru)
    {
    	struct rusage r;
    	long err = kernel_wait4(pid, stat_addr, options, ru ? &r : NULL);
    	if (err > 0) {
    		if (ru && put_compat_rusage(&r, ru))
    			return -EFAULT;
    	}
    	return err;
    }
    
    COMPAT_SYSCALL_DEFINE5(waitid,
    		int, which, compat_pid_t, pid,
    		struct compat_siginfo __user *, infop, int, options,
    		struct compat_rusage __user *, uru)
    {
    	struct rusage ru;
    	struct waitid_info info = {.status = 0};
    	long err = kernel_waitid(which, pid, &info, options, uru ? &ru : NULL);
    	int signo = 0;
    	if (err > 0) {
    		signo = SIGCHLD;
    		err = 0;
    		if (uru) {
    			/* kernel_waitid() overwrites everything in ru */
    			if (COMPAT_USE_64BIT_TIME)
    				err = copy_to_user(uru, &ru, sizeof(ru));
    			else
    				err = put_compat_rusage(&ru, uru);
    			if (err)
    				return -EFAULT;
    		}
    	}
    
    	if (!infop)
    		return err;
    
    	user_access_begin();
    	unsafe_put_user(signo, &infop->si_signo, Efault);
    	unsafe_put_user(0, &infop->si_errno, Efault);
    	unsafe_put_user(info.cause, &infop->si_code, Efault);
    	unsafe_put_user(info.pid, &infop->si_pid, Efault);
    	unsafe_put_user(info.uid, &infop->si_uid, Efault);
    	unsafe_put_user(info.status, &infop->si_status, Efault);
    	user_access_end();
    	return err;
    Efault:
    	user_access_end();
    	return -EFAULT;
    }
    #endif