// SPDX-License-Identifier: GPL-2.0-only

  /*
   *  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/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_TGID);

  		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 *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);

  #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 put_task_struct_rcu_user(struct task_struct *task)
  {
  	if (refcount_dec_and_test(&task->rcu_users))
  		call_rcu(&task->rcu, delayed_put_task_struct);
  }

  void release_task(struct task_struct *p)

  {

  	struct task_struct *leader;

  	struct pid *thread_pid;

  	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();

  	cgroup_release(p);

  	write_lock_irq(&tasklist_lock);

  	ptrace_release_task(p);

  	thread_pid = get_pid(p->thread_pid);

  	__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);

  	seccomp_filter_release(p);

  	proc_flush_pid(thread_pid);

  	put_pid(thread_pid);

  	release_thread(p);

  	put_task_struct_rcu_user(p);

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

  int rcuwait_wake_up(struct rcuwait *w)

  {

  	int ret = 0;

  	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_wake() 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_mb(); /* (B) */

  	task = rcu_dereference(w->task);
  	if (task)

  		ret = wake_up_process(task);

  	rcu_read_unlock();

  
  	return ret;

  }

  EXPORT_SYMBOL_GPL(rcuwait_wake_up);

  /*

   * 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) {

  		WRITE_ONCE(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.

  	 */

  	WRITE_ONCE(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;
  	}

  	WRITE_ONCE(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;

  	exit_mm_release(current, mm);

  	if (!mm)
  		return;

  	sync_mm_rss(mm);

  	/*
  	 * Serialize with any possible pending coredump.

  	 * We must hold mmap_lock 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.
  	 */

  	mmap_read_lock(mm);

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

  		mmap_read_unlock(mm);

  		self.task = current;

  		if (self.task->flags & PF_SIGNALED)
  			self.next = xchg(&core_state->dumper.next, &self);
  		else
  			self.task = NULL;

  		/*
  		 * 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);

  		mmap_read_lock(mm);

  	}

  	mmgrab(mm);

  	BUG_ON(mm != current->active_mm);

  	/* more a memory barrier than a real lock */

  	task_lock(current);
  	current->mm = NULL;

  	mmap_read_unlock(mm);

  	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,
  						struct list_head *dead)

  	__releases(&tasklist_lock)
  	__acquires(&tasklist_lock)
  {
  	struct pid_namespace *pid_ns = task_active_pid_ns(father);
  	struct task_struct *reaper = pid_ns->child_reaper;

  	struct task_struct *p, *n;

  
  	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);

  
  	list_for_each_entry_safe(p, n, dead, ptrace_entry) {
  		list_del_init(&p->ptrace_entry);
  		release_task(p);
  	}

  	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, dead);

  	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) {

  			RCU_INIT_POINTER(t->real_parent, reaper);
  			BUG_ON((!t->ptrace) != (rcu_access_pointer(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,
  						    PIDTYPE_TGID);

  		}

  		/*
  		 * 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);

  	tsk->exit_state = EXIT_ZOMBIE;

  	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;
  	}

  	if (autoreap) {
  		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
  ",

  			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;

  	/*
  	 * We can get here from a kernel oops, sometimes with preemption off.
  	 * Start by checking for critical errors.
  	 * Then fix up important state like USER_DS and preemption.
  	 * Then do everything else.
  	 */

  	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.
  	 */

  	force_uaccess_begin();

  	if (unlikely(in_atomic())) {
  		pr_info("note: %s[%d] exited with preempt_count %d
  ",
  			current->comm, task_pid_nr(current),
  			preempt_count());
  		preempt_count_set(PREEMPT_ENABLED);
  	}
  
  	profile_task_exit(tsk);
  	kcov_task_exit(tsk);

  	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!
  ");

  		futex_exit_recursive(tsk);

  		set_current_state(TASK_UNINTERRUPTIBLE);
  		schedule();
  	}

  	exit_signals(tsk);  /* sets PF_EXITING */

  	/* 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) {

  		/*
  		 * If the last thread of global init has exited, panic
  		 * immediately to get a useable coredump.
  		 */
  		if (unlikely(is_global_init(tsk)))
  			panic("Attempted to kill init! exitcode=0x%08x
  ",
  				tsk->signal->group_exit_code ?: (int)code);

  #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();

  	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 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 = READ_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;

  	}