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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // 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/task_io_accounting_ops.h>
 #include <linux/blkdev.h>
 #include <linux/task_work.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/io_uring.h>
 #include <linux/kprobes.h>
 #include <linux/rethook.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_exec_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);
 
     kprobe_flush_task(tsk);
     rethook_flush_task(tsk);
     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();
     dec_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
     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);
     }
 }
 
 static void coredump_task_exit(struct task_struct *tsk)
 {
     struct core_state *core_state;
 
     /*
      * Serialize with any possible pending coredump.
      * We must hold siglock around checking core_state
      * and setting PF_POSTCOREDUMP.  The core-inducing thread
      * will increment ->nr_threads for each thread in the
      * group without PF_POSTCOREDUMP set.
      */
     spin_lock_irq(&tsk->sighand->siglock);
     tsk->flags |= PF_POSTCOREDUMP;
     core_state = tsk->signal->core_state;
     spin_unlock_irq(&tsk->sighand->siglock);
     if (core_state) {
         struct core_thread self;
 
         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);
     }
 }
 
 #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;
 
     exit_mm_release(current, mm);
     if (!mm)
         return;
     sync_mm_rss(mm);
     mmap_read_lock(mm);
     mmgrab(mm);
     BUG_ON(mm != current->active_mm);
     /* more a memory barrier than a real lock */
     task_lock(current);
     /*
      * When a thread stops operating on an address space, the loop
      * in membarrier_private_expedited() may not observe that
      * tsk->mm, and the loop in membarrier_global_expedited() may
      * not observe a MEMBARRIER_STATE_GLOBAL_EXPEDITED
      * rq->membarrier_state, so those would not issue an IPI.
      * Membarrier requires a memory barrier after accessing
      * user-space memory, before clearing tsk->mm or the
      * rq->membarrier_state.
      */
     smp_mb__after_spinlock();
     local_irq_disable();
     current->mm = NULL;
     membarrier_update_current_mm(NULL);
     enter_lazy_tlb(mm, current);
     local_irq_enable();
     task_unlock(current);
     mmap_read_unlock(mm);
     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_exec_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;
 
     WARN_ON(tsk->plug);
 
     kcov_task_exit(tsk);
 
     coredump_task_exit(tsk);
     ptrace_event(PTRACE_EVENT_EXIT, code);
 
     validate_creds_for_do_exit(tsk);
 
     io_uring_files_cancel();
     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\n",
                 tsk->signal->group_exit_code ?: (int)code);
 
 #ifdef CONFIG_POSIX_TIMERS
         hrtimer_cancel(&tsk->signal->real_timer);
         exit_itimers(tsk);
 #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);
     exit_task_stack_account(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();
 }
 
 void __noreturn make_task_dead(int signr)
 {
     /*
      * Take the task off the cpu after something catastrophic has
      * happened.
      *
      * 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.
      */
     struct task_struct *tsk = current;
 
     if (unlikely(in_interrupt()))
         panic("Aiee, killing interrupt handler!");
     if (unlikely(!tsk->pid))
         panic("Attempted to kill the idle task!");
 
     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);
     }
 
     /*
      * We're taking recursive faults here in make_task_dead. 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");
         futex_exit_recursive(tsk);
         tsk->exit_state = EXIT_DEAD;
         refcount_inc(&tsk->rcu_users);
         do_task_dead();
     }
 
     do_exit(signr);
 }
 
 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 __noreturn
 do_group_exit(int exit_code)
 {
     struct signal_struct *sig = current->signal;
 
     if (sig->flags & SIGNAL_GROUP_EXIT)
         exit_code = sig->group_exit_code;
     else if (sig->group_exec_task)
         exit_code = 0;
     else if (!thread_group_empty(current)) {
         struct sighand_struct *const sighand = current->sighand;
 
         spin_lock_irq(&sighand->siglock);
         if (sig->flags & SIGNAL_GROUP_EXIT)
             /* Another thread got here before we took the lock.  */
             exit_code = sig->group_exit_code;
         else if (sig->group_exec_task)
             exit_code = 0;
         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->signal->flags & SIGNAL_GROUP_EXIT)
             ? p->signal->group_exit_code : 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-threads
          * 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;
     }
 
     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, p);
 }
 
 static bool is_effectively_child(struct wait_opts *wo, bool ptrace,
                  struct task_struct *target)
 {
     struct task_struct *parent =
         !ptrace ? target->real_parent : target->parent;
 
     return current == parent || (!(wo->wo_flags & __WNOTHREAD) &&
                      same_thread_group(current, parent));
 }
 
 /*
  * Optimization for waiting on PIDTYPE_PID. No need to iterate through child
  * and tracee lists to find the target task.
  */
 static int do_wait_pid(struct wait_opts *wo)
 {
     bool ptrace;
     struct task_struct *target;
     int retval;
 
     ptrace = false;
     target = pid_task(wo->wo_pid, PIDTYPE_TGID);
     if (target && is_effectively_child(wo, ptrace, target)) {
         retval = wait_consider_task(wo, ptrace, target);
         if (retval)
             return retval;
     }
 
     ptrace = true;
     target = pid_task(wo->wo_pid, PIDTYPE_PID);
     if (target && target->ptrace &&
         is_effectively_child(wo, ptrace, target)) {
         retval = wait_consider_task(wo, ptrace, target);
         if (retval)
             return retval;
     }
 
     return 0;
 }
 
 static long do_wait(struct wait_opts *wo)
 {
     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 || !pid_has_task(wo->wo_pid, wo->wo_type)))
         goto notask;
 
     set_current_state(TASK_INTERRUPTIBLE);
     read_lock(&tasklist_lock);
 
     if (wo->wo_type == PIDTYPE_PID) {
         retval = do_wait_pid(wo);
         if (retval)
             goto end;
     } else {
         struct task_struct *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;
     unsigned int f_flags = 0;
 
     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;
 
         pid = find_get_pid(upid);
         break;
     case P_PGID:
         type = PIDTYPE_PGID;
         if (upid < 0)
             return -EINVAL;
 
         if (upid)
             pid = find_get_pid(upid);
         else
             pid = get_task_pid(current, PIDTYPE_PGID);
         break;
     case P_PIDFD:
         type = PIDTYPE_PID;
         if (upid < 0)
             return -EINVAL;
 
         pid = pidfd_get_pid(upid, &f_flags);
         if (IS_ERR(pid))
             return PTR_ERR(pid);
 
         break;
     default:
         return -EINVAL;
     }
 
     wo.wo_type  = type;
     wo.wo_pid   = pid;
     wo.wo_flags = options;
     wo.wo_info  = infop;
     wo.wo_rusage    = ru;
     if (f_flags & O_NONBLOCK)
         wo.wo_flags |= WNOHANG;
 
     ret = do_wait(&wo);
     if (!ret && !(options & WNOHANG) && (f_flags & O_NONBLOCK))
         ret = -EAGAIN;
 
     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;
 
     if (!user_write_access_begin(infop, sizeof(*infop)))
         return -EFAULT;
 
     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_write_access_end();
     return err;
 Efault:
     user_write_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;
 }
 
 int kernel_wait(pid_t pid, int *stat)
 {
     struct wait_opts wo = {
         .wo_type    = PIDTYPE_PID,
         .wo_pid     = find_get_pid(pid),
         .wo_flags   = WEXITED,
     };
     int ret;
 
     ret = do_wait(&wo);
     if (ret > 0 && wo.wo_stat)
         *stat = wo.wo_stat;
     put_pid(wo.wo_pid);
     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 kernel_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;
 
     if (!user_write_access_begin(infop, sizeof(*infop)))
         return -EFAULT;
 
     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_write_access_end();
     return err;
 Efault:
     user_write_access_end();
     return -EFAULT;
 }
 #endif
 
 /**
  * thread_group_exited - check that a thread group has exited
  * @pid: tgid of thread group to be checked.
  *
  * Test if the thread group represented by tgid has exited (all
  * threads are zombies, dead or completely gone).
  *
  * Return: true if the thread group has exited. false otherwise.
  */
 bool thread_group_exited(struct pid *pid)
 {
     struct task_struct *task;
     bool exited;
 
     rcu_read_lock();
     task = pid_task(pid, PIDTYPE_PID);
     exited = !task ||
         (READ_ONCE(task->exit_state) && thread_group_empty(task));
     rcu_read_unlock();
 
     return exited;
 }
 EXPORT_SYMBOL(thread_group_exited);
 
 __weak void abort(void)
 {
     BUG();
 
     /* if that doesn't kill us, halt */
     panic("Oops failed to kill thread");
 }
 EXPORT_SYMBOL(abort);

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