FreeBSD/Linux Kernel Cross Reference
sys/kernel/exit.c

     /*
      *  linux/kernel/exit.c
      *
      *  Copyright (C) 1991, 1992  Linus Torvalds
      */
     
     #include <linux/mm.h>
     #include <linux/slab.h>
     #include <linux/interrupt.h>
    #include <linux/module.h>
    #include <linux/capability.h>
    #include <linux/completion.h>
    #include <linux/personality.h>
    #include <linux/tty.h>
    #include <linux/iocontext.h>
    #include <linux/key.h>
    #include <linux/security.h>
    #include <linux/cpu.h>
    #include <linux/acct.h>
    #include <linux/tsacct_kern.h>
    #include <linux/file.h>
    #include <linux/fdtable.h>
    #include <linux/binfmts.h>
    #include <linux/nsproxy.h>
    #include <linux/pid_namespace.h>
    #include <linux/ptrace.h>
    #include <linux/profile.h>
    #include <linux/mount.h>
    #include <linux/proc_fs.h>
    #include <linux/kthread.h>
    #include <linux/mempolicy.h>
    #include <linux/taskstats_kern.h>
    #include <linux/delayacct.h>
    #include <linux/freezer.h>
    #include <linux/cgroup.h>
    #include <linux/syscalls.h>
    #include <linux/signal.h>
    #include <linux/posix-timers.h>
    #include <linux/cn_proc.h>
    #include <linux/mutex.h>
    #include <linux/futex.h>
    #include <linux/pipe_fs_i.h>
    #include <linux/audit.h> /* for audit_free() */
    #include <linux/resource.h>
    #include <linux/blkdev.h>
    #include <linux/task_io_accounting_ops.h>
    #include <linux/tracehook.h>
    #include <linux/fs_struct.h>
    #include <linux/init_task.h>
    #include <linux/perf_event.h>
    #include <trace/events/sched.h>
    #include <linux/hw_breakpoint.h>
    #include <linux/oom.h>
    #include <linux/writeback.h>
    #include <linux/shm.h>
    
    #include <asm/uaccess.h>
    #include <asm/unistd.h>
    #include <asm/pgtable.h>
    #include <asm/mmu_context.h>
    
    static void exit_mm(struct task_struct * tsk);
    
    static void __unhash_process(struct task_struct *p, bool group_dead)
    {
            nr_threads--;
            detach_pid(p, PIDTYPE_PID);
            if (group_dead) {
                    detach_pid(p, PIDTYPE_PGID);
                    detach_pid(p, PIDTYPE_SID);
    
                    list_del_rcu(&p->tasks);
                    list_del_init(&p->sibling);
                    __this_cpu_dec(process_counts);
            }
            list_del_rcu(&p->thread_group);
    }
    
    /*
     * This function expects the tasklist_lock write-locked.
     */
    static void __exit_signal(struct task_struct *tsk)
    {
            struct signal_struct *sig = tsk->signal;
            bool group_dead = thread_group_leader(tsk);
            struct sighand_struct *sighand;
            struct tty_struct *uninitialized_var(tty);
    
            sighand = rcu_dereference_check(tsk->sighand,
                                            lockdep_tasklist_lock_is_held());
            spin_lock(&sighand->siglock);
    
            posix_cpu_timers_exit(tsk);
            if (group_dead) {
                    posix_cpu_timers_exit_group(tsk);
                    tty = sig->tty;
                    sig->tty = NULL;
            } else {
                    /*
                    * This can only happen if the caller is de_thread().
                    * FIXME: this is the temporary hack, we should teach
                    * posix-cpu-timers to handle this case correctly.
                    */
                   if (unlikely(has_group_leader_pid(tsk)))
                           posix_cpu_timers_exit_group(tsk);
   
                   /*
                    * If there is any task waiting for the group exit
                    * then notify it:
                    */
                   if (sig->notify_count > 0 && !--sig->notify_count)
                           wake_up_process(sig->group_exit_task);
   
                   if (tsk == sig->curr_target)
                           sig->curr_target = next_thread(tsk);
                   /*
                    * Accumulate here the counters for all threads but the
                    * group leader as they die, so they can be added into
                    * the process-wide totals when those are taken.
                    * The group leader stays around as a zombie as long
                    * as there are other threads.  When it gets reaped,
                    * the exit.c code will add its counts into these totals.
                    * We won't ever get here for the group leader, since it
                    * will have been the last reference on the signal_struct.
                    */
                   sig->utime += tsk->utime;
                   sig->stime += tsk->stime;
                   sig->gtime += tsk->gtime;
                   sig->min_flt += tsk->min_flt;
                   sig->maj_flt += tsk->maj_flt;
                   sig->nvcsw += tsk->nvcsw;
                   sig->nivcsw += tsk->nivcsw;
                   sig->inblock += task_io_get_inblock(tsk);
                   sig->oublock += task_io_get_oublock(tsk);
                   task_io_accounting_add(&sig->ioac, &tsk->ioac);
                   sig->sum_sched_runtime += tsk->se.sum_exec_runtime;
           }
   
           sig->nr_threads--;
           __unhash_process(tsk, group_dead);
   
           /*
            * Do this under ->siglock, we can race with another thread
            * doing sigqueue_free() if we have SIGQUEUE_PREALLOC signals.
            */
           flush_sigqueue(&tsk->pending);
           tsk->sighand = NULL;
           spin_unlock(&sighand->siglock);
   
           __cleanup_sighand(sighand);
           clear_tsk_thread_flag(tsk,TIF_SIGPENDING);
           if (group_dead) {
                   flush_sigqueue(&sig->shared_pending);
                   tty_kref_put(tty);
           }
   }
   
   static void delayed_put_task_struct(struct rcu_head *rhp)
   {
           struct task_struct *tsk = container_of(rhp, struct task_struct, rcu);
   
           perf_event_delayed_put(tsk);
           trace_sched_process_free(tsk);
           put_task_struct(tsk);
   }
   
   
   void release_task(struct task_struct * p)
   {
           struct task_struct *leader;
           int zap_leader;
   repeat:
           /* don't need to get the RCU readlock here - the process is dead and
            * can't be modifying its own credentials. But shut RCU-lockdep up */
           rcu_read_lock();
           atomic_dec(&__task_cred(p)->user->processes);
           rcu_read_unlock();
   
           proc_flush_task(p);
   
           write_lock_irq(&tasklist_lock);
           ptrace_release_task(p);
           __exit_signal(p);
   
           /*
            * If we are the last non-leader member of the thread
            * group, and the leader is zombie, then notify the
            * group leader's parent process. (if it wants notification.)
            */
           zap_leader = 0;
           leader = p->group_leader;
           if (leader != p && thread_group_empty(leader) && leader->exit_state == EXIT_ZOMBIE) {
                   /*
                    * If we were the last child thread and the leader has
                    * exited already, and the leader's parent ignores SIGCHLD,
                    * then we are the one who should release the leader.
                    */
                   zap_leader = do_notify_parent(leader, leader->exit_signal);
                   if (zap_leader)
                           leader->exit_state = EXIT_DEAD;
           }
   
           write_unlock_irq(&tasklist_lock);
           release_thread(p);
           call_rcu(&p->rcu, delayed_put_task_struct);
   
           p = leader;
           if (unlikely(zap_leader))
                   goto repeat;
   }
   
   /*
    * This checks not only the pgrp, but falls back on the pid if no
    * satisfactory pgrp is found. I dunno - gdb doesn't work correctly
    * without this...
    *
    * The caller must hold rcu lock or the tasklist lock.
    */
   struct pid *session_of_pgrp(struct pid *pgrp)
   {
           struct task_struct *p;
           struct pid *sid = NULL;
   
           p = pid_task(pgrp, PIDTYPE_PGID);
           if (p == NULL)
                   p = pid_task(pgrp, PIDTYPE_PID);
           if (p != NULL)
                   sid = task_session(p);
   
           return sid;
   }
   
   /*
    * Determine if a process group is "orphaned", according to the POSIX
    * definition in 2.2.2.52.  Orphaned process groups are not to be affected
    * by terminal-generated stop signals.  Newly orphaned process groups are
    * to receive a SIGHUP and a SIGCONT.
    *
    * "I ask you, have you ever known what it is to be an orphan?"
    */
   static int will_become_orphaned_pgrp(struct pid *pgrp, struct task_struct *ignored_task)
   {
           struct task_struct *p;
   
           do_each_pid_task(pgrp, PIDTYPE_PGID, p) {
                   if ((p == ignored_task) ||
                       (p->exit_state && thread_group_empty(p)) ||
                       is_global_init(p->real_parent))
                           continue;
   
                   if (task_pgrp(p->real_parent) != pgrp &&
                       task_session(p->real_parent) == task_session(p))
                           return 0;
           } while_each_pid_task(pgrp, PIDTYPE_PGID, p);
   
           return 1;
   }
   
   int is_current_pgrp_orphaned(void)
   {
           int retval;
   
           read_lock(&tasklist_lock);
           retval = will_become_orphaned_pgrp(task_pgrp(current), NULL);
           read_unlock(&tasklist_lock);
   
           return retval;
   }
   
   static bool has_stopped_jobs(struct pid *pgrp)
   {
           struct task_struct *p;
   
           do_each_pid_task(pgrp, PIDTYPE_PGID, p) {
                   if (p->signal->flags & SIGNAL_STOP_STOPPED)
                           return true;
           } while_each_pid_task(pgrp, PIDTYPE_PGID, p);
   
           return false;
   }
   
   /*
    * Check to see if any process groups have become orphaned as
    * a result of our exiting, and if they have any stopped jobs,
    * send them a SIGHUP and then a SIGCONT. (POSIX 3.2.2.2)
    */
   static void
   kill_orphaned_pgrp(struct task_struct *tsk, struct task_struct *parent)
   {
           struct pid *pgrp = task_pgrp(tsk);
           struct task_struct *ignored_task = tsk;
   
           if (!parent)
                    /* exit: our father is in a different pgrp than
                     * we are and we were the only connection outside.
                     */
                   parent = tsk->real_parent;
           else
                   /* reparent: our child is in a different pgrp than
                    * we are, and it was the only connection outside.
                    */
                   ignored_task = NULL;
   
           if (task_pgrp(parent) != pgrp &&
               task_session(parent) == task_session(tsk) &&
               will_become_orphaned_pgrp(pgrp, ignored_task) &&
               has_stopped_jobs(pgrp)) {
                   __kill_pgrp_info(SIGHUP, SEND_SIG_PRIV, pgrp);
                   __kill_pgrp_info(SIGCONT, SEND_SIG_PRIV, pgrp);
           }
   }
   
   void __set_special_pids(struct pid *pid)
   {
           struct task_struct *curr = current->group_leader;
   
           if (task_session(curr) != pid)
                   change_pid(curr, PIDTYPE_SID, pid);
   
           if (task_pgrp(curr) != pid)
                   change_pid(curr, PIDTYPE_PGID, pid);
   }
   
   /*
    * Let kernel threads use this to say that they allow a certain signal.
    * Must not be used if kthread was cloned with CLONE_SIGHAND.
    */
   int allow_signal(int sig)
   {
           if (!valid_signal(sig) || sig < 1)
                   return -EINVAL;
   
           spin_lock_irq(&current->sighand->siglock);
           /* This is only needed for daemonize()'ed kthreads */
           sigdelset(&current->blocked, sig);
           /*
            * Kernel threads handle their own signals. Let the signal code
            * know it'll be handled, so that they don't get converted to
            * SIGKILL or just silently dropped.
            */
           current->sighand->action[(sig)-1].sa.sa_handler = (void __user *)2;
           recalc_sigpending();
           spin_unlock_irq(&current->sighand->siglock);
           return 0;
   }
   
   EXPORT_SYMBOL(allow_signal);
   
   int disallow_signal(int sig)
   {
           if (!valid_signal(sig) || sig < 1)
                   return -EINVAL;
   
           spin_lock_irq(&current->sighand->siglock);
           current->sighand->action[(sig)-1].sa.sa_handler = SIG_IGN;
           recalc_sigpending();
           spin_unlock_irq(&current->sighand->siglock);
           return 0;
   }
   
   EXPORT_SYMBOL(disallow_signal);
   
   #ifdef CONFIG_MM_OWNER
   /*
    * A task is exiting.   If it owned this mm, find a new owner for the mm.
    */
   void mm_update_next_owner(struct mm_struct *mm)
   {
           struct task_struct *c, *g, *p = current;
   
   retry:
           /*
            * If the exiting or execing task is not the owner, it's
            * someone else's problem.
            */
           if (mm->owner != p)
                   return;
           /*
            * The current owner is exiting/execing and there are no other
            * candidates.  Do not leave the mm pointing to a possibly
            * freed task structure.
            */
           if (atomic_read(&mm->mm_users) <= 1) {
                   mm->owner = NULL;
                   return;
           }
   
           read_lock(&tasklist_lock);
           /*
            * Search in the children
            */
           list_for_each_entry(c, &p->children, sibling) {
                   if (c->mm == mm)
                           goto assign_new_owner;
           }
   
           /*
            * Search in the siblings
            */
           list_for_each_entry(c, &p->real_parent->children, sibling) {
                   if (c->mm == mm)
                           goto assign_new_owner;
           }
   
           /*
            * Search through everything else. We should not get
            * here often
            */
           do_each_thread(g, c) {
                   if (c->mm == mm)
                           goto assign_new_owner;
           } while_each_thread(g, c);
   
           read_unlock(&tasklist_lock);
           /*
            * We found no owner yet mm_users > 1: this implies that we are
            * most likely racing with swapoff (try_to_unuse()) or /proc or
            * ptrace or page migration (get_task_mm()).  Mark owner as NULL.
            */
           mm->owner = NULL;
           return;
   
   assign_new_owner:
           BUG_ON(c == p);
           get_task_struct(c);
           /*
            * The task_lock protects c->mm from changing.
            * We always want mm->owner->mm == mm
            */
           task_lock(c);
           /*
            * Delay read_unlock() till we have the task_lock()
            * to ensure that c does not slip away underneath us
            */
           read_unlock(&tasklist_lock);
           if (c->mm != mm) {
                   task_unlock(c);
                   put_task_struct(c);
                   goto retry;
           }
           mm->owner = c;
           task_unlock(c);
           put_task_struct(c);
   }
   #endif /* CONFIG_MM_OWNER */
   
   /*
    * Turn us into a lazy TLB process if we
    * aren't already..
    */
   static void exit_mm(struct task_struct * tsk)
   {
           struct mm_struct *mm = tsk->mm;
           struct core_state *core_state;
   
           mm_release(tsk, mm);
           if (!mm)
                   return;
           sync_mm_rss(mm);
           /*
            * Serialize with any possible pending coredump.
            * We must hold mmap_sem around checking core_state
            * and clearing tsk->mm.  The core-inducing thread
            * will increment ->nr_threads for each thread in the
            * group with ->mm != NULL.
            */
           down_read(&mm->mmap_sem);
           core_state = mm->core_state;
           if (core_state) {
                   struct core_thread self;
                   up_read(&mm->mmap_sem);
   
                   self.task = tsk;
                   self.next = xchg(&core_state->dumper.next, &self);
                   /*
                    * Implies mb(), the result of xchg() must be visible
                    * to core_state->dumper.
                    */
                   if (atomic_dec_and_test(&core_state->nr_threads))
                           complete(&core_state->startup);
   
                   for (;;) {
                           set_task_state(tsk, TASK_UNINTERRUPTIBLE);
                           if (!self.task) /* see coredump_finish() */
                                   break;
                           schedule();
                   }
                   __set_task_state(tsk, TASK_RUNNING);
                   down_read(&mm->mmap_sem);
           }
           atomic_inc(&mm->mm_count);
           BUG_ON(mm != tsk->active_mm);
           /* more a memory barrier than a real lock */
           task_lock(tsk);
           tsk->mm = NULL;
           up_read(&mm->mmap_sem);
           enter_lazy_tlb(mm, current);
           task_unlock(tsk);
           mm_update_next_owner(mm);
           mmput(mm);
   }
   
   /*
    * When we die, we re-parent all our children, and try to:
    * 1. give them to another thread in our thread group, if such a member exists
    * 2. give it to the first ancestor process which prctl'd itself as a
    *    child_subreaper for its children (like a service manager)
    * 3. give it to the init process (PID 1) in our pid namespace
    */
   static struct task_struct *find_new_reaper(struct task_struct *father)
           __releases(&tasklist_lock)
           __acquires(&tasklist_lock)
   {
           struct pid_namespace *pid_ns = task_active_pid_ns(father);
           struct task_struct *thread;
   
           thread = father;
           while_each_thread(father, thread) {
                   if (thread->flags & PF_EXITING)
                           continue;
                   if (unlikely(pid_ns->child_reaper == father))
                           pid_ns->child_reaper = thread;
                   return thread;
           }
   
           if (unlikely(pid_ns->child_reaper == father)) {
                   write_unlock_irq(&tasklist_lock);
                   if (unlikely(pid_ns == &init_pid_ns)) {
                           panic("Attempted to kill init! exitcode=0x%08x\n",
                                   father->signal->group_exit_code ?:
                                           father->exit_code);
                   }
   
                   zap_pid_ns_processes(pid_ns);
                   write_lock_irq(&tasklist_lock);
           } else if (father->signal->has_child_subreaper) {
                   struct task_struct *reaper;
   
                   /*
                    * Find the first ancestor marked as child_subreaper.
                    * Note that the code below checks same_thread_group(reaper,
                    * pid_ns->child_reaper).  This is what we need to DTRT in a
                    * PID namespace. However we still need the check above, see
                    * http://marc.info/?l=linux-kernel&m=131385460420380
                    */
                   for (reaper = father->real_parent;
                        reaper != &init_task;
                        reaper = reaper->real_parent) {
                           if (same_thread_group(reaper, pid_ns->child_reaper))
                                   break;
                           if (!reaper->signal->is_child_subreaper)
                                   continue;
                           thread = reaper;
                           do {
                                   if (!(thread->flags & PF_EXITING))
                                           return reaper;
                           } while_each_thread(reaper, thread);
                   }
           }
   
           return pid_ns->child_reaper;
   }
   
   /*
   * Any that need to be release_task'd are put on the @dead list.
    */
   static void reparent_leader(struct task_struct *father, struct task_struct *p,
                                   struct list_head *dead)
   {
           list_move_tail(&p->sibling, &p->real_parent->children);
   
           if (p->exit_state == EXIT_DEAD)
                   return;
           /*
            * If this is a threaded reparent there is no need to
            * notify anyone anything has happened.
            */
           if (same_thread_group(p->real_parent, father))
                   return;
   
           /* We don't want people slaying init.  */
           p->exit_signal = SIGCHLD;
   
           /* If it has exited notify the new parent about this child's death. */
           if (!p->ptrace &&
               p->exit_state == EXIT_ZOMBIE && thread_group_empty(p)) {
                   if (do_notify_parent(p, p->exit_signal)) {
                           p->exit_state = EXIT_DEAD;
                           list_move_tail(&p->sibling, dead);
                   }
           }
   
           kill_orphaned_pgrp(p, father);
   }
   
   static void forget_original_parent(struct task_struct *father)
   {
           struct task_struct *p, *n, *reaper;
           LIST_HEAD(dead_children);
   
           write_lock_irq(&tasklist_lock);
           /*
            * Note that exit_ptrace() and find_new_reaper() might
            * drop tasklist_lock and reacquire it.
            */
           exit_ptrace(father);
           reaper = find_new_reaper(father);
   
           list_for_each_entry_safe(p, n, &father->children, sibling) {
                   struct task_struct *t = p;
                   do {
                           t->real_parent = reaper;
                           if (t->parent == father) {
                                   BUG_ON(t->ptrace);
                                   t->parent = t->real_parent;
                           }
                           if (t->pdeath_signal)
                                   group_send_sig_info(t->pdeath_signal,
                                                       SEND_SIG_NOINFO, t);
                   } while_each_thread(p, t);
                   reparent_leader(father, p, &dead_children);
           }
           write_unlock_irq(&tasklist_lock);
   
           BUG_ON(!list_empty(&father->children));
   
           list_for_each_entry_safe(p, n, &dead_children, sibling) {
                   list_del_init(&p->sibling);
                   release_task(p);
           }
   }
   
   /*
    * Send signals to all our closest relatives so that they know
    * to properly mourn us..
    */
   static void exit_notify(struct task_struct *tsk, int group_dead)
   {
           bool autoreap;
   
           /*
            * This does two things:
            *
            * A.  Make init inherit all the child processes
            * B.  Check to see if any process groups have become orphaned
            *      as a result of our exiting, and if they have any stopped
            *      jobs, send them a SIGHUP and then a SIGCONT.  (POSIX 3.2.2.2)
            */
           forget_original_parent(tsk);
           exit_task_namespaces(tsk);
   
           write_lock_irq(&tasklist_lock);
           if (group_dead)
                   kill_orphaned_pgrp(tsk->group_leader, NULL);
   
           if (unlikely(tsk->ptrace)) {
                   int sig = thread_group_leader(tsk) &&
                                   thread_group_empty(tsk) &&
                                   !ptrace_reparented(tsk) ?
                           tsk->exit_signal : SIGCHLD;
                   autoreap = do_notify_parent(tsk, sig);
           } else if (thread_group_leader(tsk)) {
                   autoreap = thread_group_empty(tsk) &&
                           do_notify_parent(tsk, tsk->exit_signal);
           } else {
                   autoreap = true;
           }
   
           tsk->exit_state = autoreap ? EXIT_DEAD : EXIT_ZOMBIE;
   
           /* mt-exec, de_thread() is waiting for group leader */
           if (unlikely(tsk->signal->notify_count < 0))
                   wake_up_process(tsk->signal->group_exit_task);
           write_unlock_irq(&tasklist_lock);
   
           /* If the process is dead, release it - nobody will wait for it */
           if (autoreap)
                   release_task(tsk);
   }
   
   #ifdef CONFIG_DEBUG_STACK_USAGE
   static void check_stack_usage(void)
   {
           static DEFINE_SPINLOCK(low_water_lock);
           static int lowest_to_date = THREAD_SIZE;
           unsigned long free;
   
           free = stack_not_used(current);
   
           if (free >= lowest_to_date)
                   return;
   
           spin_lock(&low_water_lock);
           if (free < lowest_to_date) {
                   printk(KERN_WARNING "%s (%d) used greatest stack depth: "
                                   "%lu bytes left\n",
                                   current->comm, task_pid_nr(current), free);
                   lowest_to_date = free;
           }
           spin_unlock(&low_water_lock);
   }
   #else
   static inline void check_stack_usage(void) {}
   #endif
   
   void do_exit(long code)
   {
           struct task_struct *tsk = current;
           int group_dead;
   
           profile_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)) {
                   printk(KERN_ALERT
                           "Fixing recursive fault but reboot is needed!\n");
                   /*
                    * We can do this unlocked here. The futex code uses
                    * this flag just to verify whether the pi state
                    * cleanup has been done or not. In the worst case it
                    * loops once more. We pretend that the cleanup was
                    * done as there is no way to return. Either the
                    * OWNER_DIED bit is set by now or we push the blocked
                    * task into the wait for ever nirwana as well.
                    */
                   tsk->flags |= PF_EXITPIDONE;
                   set_current_state(TASK_UNINTERRUPTIBLE);
                   schedule();
           }
   
           exit_signals(tsk);  /* sets PF_EXITING */
           /*
            * tsk->flags are checked in the futex code to protect against
            * an exiting task cleaning up the robust pi futexes.
            */
           smp_mb();
           raw_spin_unlock_wait(&tsk->pi_lock);
   
           if (unlikely(in_atomic()))
                   printk(KERN_INFO "note: %s[%d] exited with preempt_count %d\n",
                                   current->comm, task_pid_nr(current),
                                   preempt_count());
   
           acct_update_integrals(tsk);
           /* sync mm's RSS info before statistics gathering */
           if (tsk->mm)
                   sync_mm_rss(tsk->mm);
           group_dead = atomic_dec_and_test(&tsk->signal->live);
           if (group_dead) {
                   hrtimer_cancel(&tsk->signal->real_timer);
                   exit_itimers(tsk->signal);
                   if (tsk->mm)
                           setmax_mm_hiwater_rss(&tsk->signal->maxrss, tsk->mm);
           }
           acct_collect(code, group_dead);
           if (group_dead)
                   tty_audit_exit();
           audit_free(tsk);
   
           tsk->exit_code = code;
           taskstats_exit(tsk, group_dead);
   
           exit_mm(tsk);
   
           if (group_dead)
                   acct_process();
           trace_sched_process_exit(tsk);
   
           exit_sem(tsk);
           exit_shm(tsk);
           exit_files(tsk);
           exit_fs(tsk);
           exit_task_work(tsk);
           check_stack_usage();
           exit_thread();
   
           /*
            * Flush inherited counters to the parent - before the parent
            * gets woken up by child-exit notifications.
            *
            * because of cgroup mode, must be called before cgroup_exit()
            */
           perf_event_exit_task(tsk);
   
           cgroup_exit(tsk, 1);
   
           if (group_dead)
                   disassociate_ctty(1);
   
           module_put(task_thread_info(tsk)->exec_domain->module);
   
           proc_exit_connector(tsk);
   
           /*
            * FIXME: do that only when needed, using sched_exit tracepoint
            */
           ptrace_put_breakpoints(tsk);
   
           exit_notify(tsk, group_dead);
   #ifdef CONFIG_NUMA
           task_lock(tsk);
           mpol_put(tsk->mempolicy);
           tsk->mempolicy = NULL;
           task_unlock(tsk);
   #endif
   #ifdef CONFIG_FUTEX
           if (unlikely(current->pi_state_cache))
                   kfree(current->pi_state_cache);
   #endif
           /*
            * Make sure we are holding no locks:
            */
           debug_check_no_locks_held(tsk);
           /*
            * We can do this unlocked here. The futex code uses this flag
            * just to verify whether the pi state cleanup has been done
            * or not. In the worst case it loops once more.
            */
           tsk->flags |= PF_EXITPIDONE;
   
           if (tsk->io_context)
                   exit_io_context(tsk);
   
           if (tsk->splice_pipe)
                   __free_pipe_info(tsk->splice_pipe);
   
           if (tsk->task_frag.page)
                   put_page(tsk->task_frag.page);
   
           validate_creds_for_do_exit(tsk);
   
           preempt_disable();
           if (tsk->nr_dirtied)
                   __this_cpu_add(dirty_throttle_leaks, tsk->nr_dirtied);
           exit_rcu();
   
           /*
            * The setting of TASK_RUNNING by try_to_wake_up() may be delayed
            * when the following two conditions become true.
            *   - There is race condition of mmap_sem (It is acquired by
            *     exit_mm()), and
            *   - SMI occurs before setting TASK_RUNINNG.
            *     (or hypervisor of virtual machine switches to other guest)
            *  As a result, we may become TASK_RUNNING after becoming TASK_DEAD
            *
            * To avoid it, we have to wait for releasing tsk->pi_lock which
            * is held by try_to_wake_up()
            */
           smp_mb();
           raw_spin_unlock_wait(&tsk->pi_lock);
   
           /* causes final put_task_struct in finish_task_switch(). */
           tsk->state = TASK_DEAD;
           tsk->flags |= PF_NOFREEZE;      /* tell freezer to ignore us */
           schedule();
           BUG();
           /* Avoid "noreturn function does return".  */
           for (;;)
                   cpu_relax();    /* For when BUG is null */
   }
   
   EXPORT_SYMBOL_GPL(do_exit);
   
   void complete_and_exit(struct completion *comp, long code)
   {
           if (comp)
                   complete(comp);
   
           do_exit(code);
   }
   
   EXPORT_SYMBOL(complete_and_exit);
   
   SYSCALL_DEFINE1(exit, int, error_code)
   {
           do_exit((error_code&0xff)<<8);
   }
   
   /*
    * Take down every thread in the group.  This is called by fatal signals
    * as well as by sys_exit_group (below).
    */
   void
   do_group_exit(int exit_code)
   {
           struct signal_struct *sig = current->signal;
   
           BUG_ON(exit_code & 0x80); /* core dumps don't get here */
   
           if (signal_group_exit(sig))
                   exit_code = sig->group_exit_code;
           else if (!thread_group_empty(current)) {
                   struct sighand_struct *const sighand = current->sighand;
                   spin_lock_irq(&sighand->siglock);
                   if (signal_group_exit(sig))
                           /* Another thread got here before we took the lock.  */
                           exit_code = sig->group_exit_code;
                   else {
                           sig->group_exit_code = exit_code;
                           sig->flags = SIGNAL_GROUP_EXIT;
                           zap_other_threads(current);
                   }
                   spin_unlock_irq(&sighand->siglock);
           }
   
           do_exit(exit_code);
           /* NOTREACHED */
   }
   
   /*
    * this kills every thread in the thread group. Note that any externally
    * wait4()-ing process will get the correct exit code - even if this
    * thread is not the thread group leader.
    */
   SYSCALL_DEFINE1(exit_group, int, error_code)
   {
           do_group_exit((error_code & 0xff) << 8);
           /* NOTREACHED */
           return 0;
   }
   
   struct wait_opts {
           enum pid_type           wo_type;
           int                     wo_flags;
           struct pid              *wo_pid;
   
           struct siginfo __user   *wo_info;
           int __user              *wo_stat;
           struct rusage __user    *wo_rusage;
   
           wait_queue_t            child_wait;
           int                     notask_error;
   };
   
   static inline
   struct pid *task_pid_type(struct task_struct *task, enum pid_type type)
   {
           if (type != PIDTYPE_PID)
                   task = task->group_leader;
           return task->pids[type].pid;
   }
   
   static int eligible_pid(struct wait_opts *wo, struct task_struct *p)
   {
           return  wo->wo_type == PIDTYPE_MAX ||
                   task_pid_type(p, wo->wo_type) == wo->wo_pid;
   }
   
   static int eligible_child(struct wait_opts *wo, struct task_struct *p)
   {
           if (!eligible_pid(wo, p))
                   return 0;
           /* Wait for all children (clone and not) if __WALL is set;
            * otherwise, wait for clone children *only* if __WCLONE is
            * set; otherwise, wait for non-clone children *only*.  (Note:
            * A "clone" child here is one that reports to its parent
            * using a signal other than SIGCHLD.) */
           if (((p->exit_signal != SIGCHLD) ^ !!(wo->wo_flags & __WCLONE))
               && !(wo->wo_flags & __WALL))
                   return 0;
   
           return 1;
   }
   
   static int wait_noreap_copyout(struct wait_opts *wo, struct task_struct *p,
                                   pid_t pid, uid_t uid, int why, int status)
   {
           struct siginfo __user *infop;
           int retval = wo->wo_rusage
                   ? getrusage(p, RUSAGE_BOTH, wo->wo_rusage) : 0;
   
           put_task_struct(p);
           infop = wo->wo_info;
           if (infop) {
                   if (!retval)
                           retval = put_user(SIGCHLD, &infop->si_signo);
                  if (!retval)
                          retval = put_user(0, &infop->si_errno);
                  if (!retval)
                          retval = put_user((short)why, &infop->si_code);
                  if (!retval)
                          retval = put_user(pid, &infop->si_pid);
                  if (!retval)
                          retval = put_user(uid, &infop->si_uid);
                  if (!retval)
                          retval = put_user(status, &infop->si_status);
          }
          if (!retval)
                  retval = pid;
          return retval;
  }
  
  /*
   * Handle sys_wait4 work for one task in state EXIT_ZOMBIE.  We hold
   * read_lock(&tasklist_lock) on entry.  If we return zero, we still hold
   * the lock and this task is uninteresting.  If we return nonzero, we have
   * released the lock and the system call should return.
   */
  static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)
  {
          unsigned long state;
          int retval, status, traced;
          pid_t pid = task_pid_vnr(p);
          uid_t uid = from_kuid_munged(current_user_ns(), task_uid(p));
          struct siginfo __user *infop;
  
          if (!likely(wo->wo_flags & WEXITED))
                  return 0;
  
          if (unlikely(wo->wo_flags & WNOWAIT)) {
                  int exit_code = p->exit_code;
                  int why;
  
                  get_task_struct(p);
                  read_unlock(&tasklist_lock);
                  if ((exit_code & 0x7f) == 0) {
                          why = CLD_EXITED;
                          status = exit_code >> 8;
                  } else {
                          why = (exit_code & 0x80) ? CLD_DUMPED : CLD_KILLED;
                          status = exit_code & 0x7f;
                  }
                  return wait_noreap_copyout(wo, p, pid, uid, why, status);
          }
  
          /*
           * Try to move the task's state to DEAD
           * only one thread is allowed to do this:
           */
          state = xchg(&p->exit_state, EXIT_DEAD);
          if (state != EXIT_ZOMBIE) {
                  BUG_ON(state != EXIT_DEAD);
                  return 0;
          }
  
          traced = ptrace_reparented(p);
          /*
           * It can be ptraced but not reparented, check
           * thread_group_leader() to filter out sub-threads.
           */
          if (likely(!traced) && thread_group_leader(p)) {
                  struct signal_struct *psig;
                  struct signal_struct *sig;
                  unsigned long maxrss;
                  cputime_t tgutime, tgstime;
  
                  /*
                   * The resource counters for the group leader are in its
                   * own task_struct.  Those for dead threads in the group
                   * are in its signal_struct, as are those for the child
                   * processes it has previously reaped.  All these
                   * accumulate in the parent's signal_struct c* fields.
                   *
                   * We don't bother to take a lock here to protect these
                   * p->signal fields, because they are only touched by
                   * __exit_signal, which runs with tasklist_lock
                   * write-locked anyway, and so is excluded here.  We do
                   * need to protect the access to parent->signal fields,
                   * as other threads in the parent group can be right
                   * here reaping other children at the same time.
                   *
                   * We use thread_group_cputime_adjusted() to get times for the thread
                   * group, which consolidates times for all threads in the
                   * group including the group leader.
                   */
                  thread_group_cputime_adjusted(p, &tgutime, &tgstime);
                  spin_lock_irq(&p->real_parent->sighand->siglock);
                  psig = p->real_parent->signal;
                  sig = p->signal;
                  psig->cutime += tgutime + sig->cutime;
                  psig->cstime += tgstime + sig->cstime;
                  psig->cgtime += p->gtime + sig->gtime + sig->cgtime;
                  psig->cmin_flt +=
                          p->min_flt + sig->min_flt + sig->cmin_flt;
                  psig->cmaj_flt +=
                          p->maj_flt + sig->maj_flt + sig->cmaj_flt;
                  psig->cnvcsw +=
                          p->nvcsw + sig->nvcsw + sig->cnvcsw;
                  psig->cnivcsw +=
                          p->nivcsw + sig->nivcsw + sig->cnivcsw;
                  psig->cinblock +=
                          task_io_get_inblock(p) +
                          sig->inblock + sig->cinblock;
                  psig->coublock +=
                          task_io_get_oublock(p) +
                          sig->oublock + sig->coublock;
                  maxrss = max(sig->maxrss, sig->cmaxrss);
                  if (psig->cmaxrss < maxrss)
                          psig->cmaxrss = maxrss;
                  task_io_accounting_add(&psig->ioac, &p->ioac);
                  task_io_accounting_add(&psig->ioac, &sig->ioac);
                  spin_unlock_irq(&p->real_parent->sighand->siglock);
          }
  
          /*
           * Now we are sure this task is interesting, and no other
           * thread can reap it because we set its state to EXIT_DEAD.
           */
          read_unlock(&tasklist_lock);
  
          retval = wo->wo_rusage
                  ? getrusage(p, RUSAGE_BOTH, wo->wo_rusage) : 0;
          status = (p->signal->flags & SIGNAL_GROUP_EXIT)
                  ? p->signal->group_exit_code : p->exit_code;
          if (!retval && wo->wo_stat)
                  retval = put_user(status, wo->wo_stat);
  
          infop = wo->wo_info;
          if (!retval && infop)
                  retval = put_user(SIGCHLD, &infop->si_signo);
          if (!retval && infop)
                  retval = put_user(0, &infop->si_errno);
          if (!retval && infop) {
                  int why;
  
                  if ((status & 0x7f) == 0) {
                          why = CLD_EXITED;
                          status >>= 8;
                  } else {
                          why = (status & 0x80) ? CLD_DUMPED : CLD_KILLED;
                          status &= 0x7f;
                  }
                  retval = put_user((short)why, &infop->si_code);
                  if (!retval)
                          retval = put_user(status, &infop->si_status);
          }
          if (!retval && infop)
                  retval = put_user(pid, &infop->si_pid);
          if (!retval && infop)
                  retval = put_user(uid, &infop->si_uid);
          if (!retval)
                  retval = pid;
  
          if (traced) {
                  write_lock_irq(&tasklist_lock);
                  /* We dropped tasklist, ptracer could die and untrace */
                  ptrace_unlink(p);
                  /*
                   * If this is not a sub-thread, notify the parent.
                   * If parent wants a zombie, don't release it now.
                   */
                  if (thread_group_leader(p) &&
                      !do_notify_parent(p, p->exit_signal)) {
                          p->exit_state = EXIT_ZOMBIE;
                          p = NULL;
                  }
                  write_unlock_irq(&tasklist_lock);
          }
          if (p != NULL)
                  release_task(p);
  
          return retval;
  }
  
  static int *task_stopped_code(struct task_struct *p, bool ptrace)
  {
          if (ptrace) {
                  if (task_is_stopped_or_traced(p) &&
                      !(p->jobctl & JOBCTL_LISTENING))
                          return &p->exit_code;
          } else {
                  if (p->signal->flags & SIGNAL_STOP_STOPPED)
                          return &p->signal->group_exit_code;
          }
          return NULL;
  }
  
  /**
   * wait_task_stopped - Wait for %TASK_STOPPED or %TASK_TRACED
   * @wo: wait options
   * @ptrace: is the wait for ptrace
   * @p: task to wait for
   *
   * Handle sys_wait4() work for %p in state %TASK_STOPPED or %TASK_TRACED.
   *
   * CONTEXT:
   * read_lock(&tasklist_lock), which is released if return value is
   * non-zero.  Also, grabs and releases @p->sighand->siglock.
   *
   * RETURNS:
   * 0 if wait condition didn't exist and search for other wait conditions
   * should continue.  Non-zero return, -errno on failure and @p's pid on
   * success, implies that tasklist_lock is released and wait condition
   * search should terminate.
   */
  static int wait_task_stopped(struct wait_opts *wo,
                                  int ptrace, struct task_struct *p)
  {
          struct siginfo __user *infop;
          int retval, exit_code, *p_code, why;
          uid_t uid = 0; /* unneeded, required by compiler */
          pid_t pid;
  
          /*
           * Traditionally we see ptrace'd stopped tasks regardless of options.
           */
          if (!ptrace && !(wo->wo_flags & WUNTRACED))
                  return 0;
  
          if (!task_stopped_code(p, ptrace))
                  return 0;
  
          exit_code = 0;
          spin_lock_irq(&p->sighand->siglock);
  
          p_code = task_stopped_code(p, ptrace);
          if (unlikely(!p_code))
                  goto unlock_sig;
  
          exit_code = *p_code;
          if (!exit_code)
                  goto unlock_sig;
  
          if (!unlikely(wo->wo_flags & WNOWAIT))
                  *p_code = 0;
  
          uid = from_kuid_munged(current_user_ns(), task_uid(p));
  unlock_sig:
          spin_unlock_irq(&p->sighand->siglock);
          if (!exit_code)
                  return 0;
  
          /*
           * Now we are pretty sure this task is interesting.
           * Make sure it doesn't get reaped out from under us while we
           * give up the lock and then examine it below.  We don't want to
           * keep holding onto the tasklist_lock while we call getrusage and
           * possibly take page faults for user memory.
           */
          get_task_struct(p);
          pid = task_pid_vnr(p);
          why = ptrace ? CLD_TRAPPED : CLD_STOPPED;
          read_unlock(&tasklist_lock);
  
          if (unlikely(wo->wo_flags & WNOWAIT))
                  return wait_noreap_copyout(wo, p, pid, uid, why, exit_code);
  
          retval = wo->wo_rusage
                  ? getrusage(p, RUSAGE_BOTH, wo->wo_rusage) : 0;
          if (!retval && wo->wo_stat)
                  retval = put_user((exit_code << 8) | 0x7f, wo->wo_stat);
  
          infop = wo->wo_info;
          if (!retval && infop)
                  retval = put_user(SIGCHLD, &infop->si_signo);
          if (!retval && infop)
                  retval = put_user(0, &infop->si_errno);
          if (!retval && infop)
                  retval = put_user((short)why, &infop->si_code);
          if (!retval && infop)
                  retval = put_user(exit_code, &infop->si_status);
          if (!retval && infop)
                  retval = put_user(pid, &infop->si_pid);
          if (!retval && infop)
                  retval = put_user(uid, &infop->si_uid);
          if (!retval)
                  retval = pid;
          put_task_struct(p);
  
          BUG_ON(!retval);
          return retval;
  }
  
  /*
   * Handle do_wait work for one task in a live, non-stopped state.
   * read_lock(&tasklist_lock) on entry.  If we return zero, we still hold
   * the lock and this task is uninteresting.  If we return nonzero, we have
   * released the lock and the system call should return.
   */
  static int wait_task_continued(struct wait_opts *wo, struct task_struct *p)
  {
          int retval;
          pid_t pid;
          uid_t uid;
  
          if (!unlikely(wo->wo_flags & WCONTINUED))
                  return 0;
  
          if (!(p->signal->flags & SIGNAL_STOP_CONTINUED))
                  return 0;
  
          spin_lock_irq(&p->sighand->siglock);
          /* Re-check with the lock held.  */
          if (!(p->signal->flags & SIGNAL_STOP_CONTINUED)) {
                  spin_unlock_irq(&p->sighand->siglock);
                  return 0;
          }
          if (!unlikely(wo->wo_flags & WNOWAIT))
                  p->signal->flags &= ~SIGNAL_STOP_CONTINUED;
          uid = from_kuid_munged(current_user_ns(), task_uid(p));
          spin_unlock_irq(&p->sighand->siglock);
  
          pid = task_pid_vnr(p);
          get_task_struct(p);
          read_unlock(&tasklist_lock);
  
          if (!wo->wo_info) {
                  retval = wo->wo_rusage
                          ? getrusage(p, RUSAGE_BOTH, wo->wo_rusage) : 0;
                  put_task_struct(p);
                  if (!retval && wo->wo_stat)
                          retval = put_user(0xffff, wo->wo_stat);
                  if (!retval)
                          retval = pid;
          } else {
                  retval = wait_noreap_copyout(wo, p, pid, uid,
                                               CLD_CONTINUED, SIGCONT);
                  BUG_ON(retval == 0);
          }
  
          return retval;
  }
  
  /*
   * Consider @p for a wait by @parent.
   *
   * -ECHILD should be in ->notask_error before the first call.
   * Returns nonzero for a final return, when we have unlocked tasklist_lock.
   * Returns zero if the search for a child should continue;
   * then ->notask_error is 0 if @p is an eligible child,
   * or another error from security_task_wait(), or still -ECHILD.
   */
  static int wait_consider_task(struct wait_opts *wo, int ptrace,
                                  struct task_struct *p)
  {
          int ret = eligible_child(wo, p);
          if (!ret)
                  return ret;
  
          ret = security_task_wait(p);
          if (unlikely(ret < 0)) {
                  /*
                   * If we have not yet seen any eligible child,
                   * then let this error code replace -ECHILD.
                   * A permission error will give the user a clue
                   * to look for security policy problems, rather
                   * than for mysterious wait bugs.
                   */
                  if (wo->notask_error)
                          wo->notask_error = ret;
                  return 0;
          }
  
          /* dead body doesn't have much to contribute */
          if (unlikely(p->exit_state == EXIT_DEAD)) {
                  /*
                   * But do not ignore this task until the tracer does
                   * wait_task_zombie()->do_notify_parent().
                   */
                  if (likely(!ptrace) && unlikely(ptrace_reparented(p)))
                          wo->notask_error = 0;
                  return 0;
          }
  
          /* slay zombie? */
          if (p->exit_state == EXIT_ZOMBIE) {
                  /*
                   * A zombie ptracee is only visible to its ptracer.
                   * Notification and reaping will be cascaded to the real
                   * parent when the ptracer detaches.
                   */
                  if (likely(!ptrace) && unlikely(p->ptrace)) {
                          /* it will become visible, clear notask_error */
                          wo->notask_error = 0;
                          return 0;
                  }
  
                  /* we don't reap group leaders with subthreads */
                  if (!delay_group_leader(p))
                          return wait_task_zombie(wo, p);
  
                  /*
                   * Allow access to stopped/continued state via zombie by
                   * falling through.  Clearing of notask_error is complex.
                   *
                   * When !@ptrace:
                   *
                   * If WEXITED is set, notask_error should naturally be
                   * cleared.  If not, subset of WSTOPPED|WCONTINUED is set,
                   * so, if there are live subthreads, there are events to
                   * wait for.  If all subthreads are dead, it's still safe
                   * to clear - this function will be called again in finite
                   * amount time once all the subthreads are released and
                   * will then return without clearing.
                   *
                   * When @ptrace:
                   *
                   * Stopped state is per-task and thus can't change once the
                   * target task dies.  Only continued and exited can happen.
                   * Clear notask_error if WCONTINUED | WEXITED.
                   */
                  if (likely(!ptrace) || (wo->wo_flags & (WCONTINUED | WEXITED)))
                          wo->notask_error = 0;
          } else {
                  /*
                   * If @p is ptraced by a task in its real parent's group,
                   * hide group stop/continued state when looking at @p as
                   * the real parent; otherwise, a single stop can be
                   * reported twice as group and ptrace stops.
                   *
                   * If a ptracer wants to distinguish the two events for its
                   * own children, it should create a separate process which
                   * takes the role of real parent.
                   */
                  if (likely(!ptrace) && p->ptrace && !ptrace_reparented(p))
                          return 0;
  
                  /*
                   * @p is alive and it's gonna stop, continue or exit, so
                   * there always is something to wait for.
                   */
                  wo->notask_error = 0;
          }
  
          /*
           * Wait for stopped.  Depending on @ptrace, different stopped state
           * is used and the two don't interact with each other.
           */
          ret = wait_task_stopped(wo, ptrace, p);
          if (ret)
                  return ret;
  
          /*
           * Wait for continued.  There's only one continued state and the
           * ptracer can consume it which can confuse the real parent.  Don't
           * use WCONTINUED from ptracer.  You don't need or want it.
           */
          return wait_task_continued(wo, p);
  }
  
  /*
   * Do the work of do_wait() for one thread in the group, @tsk.
   *
   * -ECHILD should be in ->notask_error before the first call.
   * Returns nonzero for a final return, when we have unlocked tasklist_lock.
   * Returns zero if the search for a child should continue; then
   * ->notask_error is 0 if there were any eligible children,
   * or another error from security_task_wait(), or still -ECHILD.
   */
  static int do_wait_thread(struct wait_opts *wo, struct task_struct *tsk)
  {
          struct task_struct *p;
  
          list_for_each_entry(p, &tsk->children, sibling) {
                  int ret = wait_consider_task(wo, 0, p);
                  if (ret)
                          return ret;
          }
  
          return 0;
  }
  
  static int ptrace_do_wait(struct wait_opts *wo, struct task_struct *tsk)
  {
          struct task_struct *p;
  
          list_for_each_entry(p, &tsk->ptraced, ptrace_entry) {
                  int ret = wait_consider_task(wo, 1, p);
                  if (ret)
                          return ret;
          }
  
          return 0;
  }
  
  static int child_wait_callback(wait_queue_t *wait, unsigned mode,
                                  int sync, void *key)
  {
          struct wait_opts *wo = container_of(wait, struct wait_opts,
                                                  child_wait);
          struct task_struct *p = key;
  
          if (!eligible_pid(wo, p))
                  return 0;
  
          if ((wo->wo_flags & __WNOTHREAD) && wait->private != p->parent)
                  return 0;
  
          return default_wake_function(wait, mode, sync, key);
  }
  
  void __wake_up_parent(struct task_struct *p, struct task_struct *parent)
  {
          __wake_up_sync_key(&parent->signal->wait_chldexit,
                                  TASK_INTERRUPTIBLE, 1, p);
  }
  
  static long do_wait(struct wait_opts *wo)
  {
          struct task_struct *tsk;
          int retval;
  
          trace_sched_process_wait(wo->wo_pid);
  
          init_waitqueue_func_entry(&wo->child_wait, child_wait_callback);
          wo->child_wait.private = current;
          add_wait_queue(&current->signal->wait_chldexit, &wo->child_wait);
  repeat:
          /*
           * If there is nothing that can match our critiera just get out.
           * We will clear ->notask_error to zero if we see any child that
           * might later match our criteria, even if we are not able to reap
           * it yet.
           */
          wo->notask_error = -ECHILD;
          if ((wo->wo_type < PIDTYPE_MAX) &&
             (!wo->wo_pid || hlist_empty(&wo->wo_pid->tasks[wo->wo_type])))
                  goto notask;
  
          set_current_state(TASK_INTERRUPTIBLE);
          read_lock(&tasklist_lock);
          tsk = current;
          do {
                  retval = do_wait_thread(wo, tsk);
                  if (retval)
                          goto end;
  
                  retval = ptrace_do_wait(wo, tsk);
                  if (retval)
                          goto end;
  
                  if (wo->wo_flags & __WNOTHREAD)
                          break;
          } while_each_thread(current, tsk);
          read_unlock(&tasklist_lock);
  
  notask:
          retval = wo->notask_error;
          if (!retval && !(wo->wo_flags & WNOHANG)) {
                  retval = -ERESTARTSYS;
                  if (!signal_pending(current)) {
                          schedule();
                          goto repeat;
                  }
          }
  end:
          __set_current_state(TASK_RUNNING);
          remove_wait_queue(&current->signal->wait_chldexit, &wo->child_wait);
          return retval;
  }
  
  SYSCALL_DEFINE5(waitid, int, which, pid_t, upid, struct siginfo __user *,
                  infop, int, options, struct rusage __user *, ru)
  {
          struct wait_opts wo;
          struct pid *pid = NULL;
          enum pid_type type;
          long ret;
  
          if (options & ~(WNOHANG|WNOWAIT|WEXITED|WSTOPPED|WCONTINUED))
                  return -EINVAL;
          if (!(options & (WEXITED|WSTOPPED|WCONTINUED)))
                  return -EINVAL;
  
          switch (which) {
          case P_ALL:
                  type = PIDTYPE_MAX;
                  break;
          case P_PID:
                  type = PIDTYPE_PID;
                  if (upid <= 0)
                          return -EINVAL;
                  break;
          case P_PGID:
                  type = PIDTYPE_PGID;
                  if (upid <= 0)
                          return -EINVAL;
                  break;
          default:
                  return -EINVAL;
          }
  
          if (type < PIDTYPE_MAX)
                  pid = find_get_pid(upid);
  
          wo.wo_type      = type;
          wo.wo_pid       = pid;
          wo.wo_flags     = options;
          wo.wo_info      = infop;
          wo.wo_stat      = NULL;
          wo.wo_rusage    = ru;
          ret = do_wait(&wo);
  
          if (ret > 0) {
                  ret = 0;
          } else if (infop) {
                  /*
                   * For a WNOHANG return, clear out all the fields
                   * we would set so the user can easily tell the
                   * difference.
                   */
                  if (!ret)
                          ret = put_user(0, &infop->si_signo);
                  if (!ret)
                          ret = put_user(0, &infop->si_errno);
                  if (!ret)
                          ret = put_user(0, &infop->si_code);
                  if (!ret)
                          ret = put_user(0, &infop->si_pid);
                  if (!ret)
                          ret = put_user(0, &infop->si_uid);
                  if (!ret)
                          ret = put_user(0, &infop->si_status);
          }
  
          put_pid(pid);
  
          /* avoid REGPARM breakage on x86: */
          asmlinkage_protect(5, ret, which, upid, infop, options, ru);
          return ret;
  }
  
  SYSCALL_DEFINE4(wait4, pid_t, upid, int __user *, stat_addr,
                  int, options, struct rusage __user *, ru)
  {
          struct wait_opts wo;
          struct pid *pid = NULL;
          enum pid_type type;
          long ret;
  
          if (options & ~(WNOHANG|WUNTRACED|WCONTINUED|
                          __WNOTHREAD|__WCLONE|__WALL))
                  return -EINVAL;
  
          if (upid == -1)
                  type = PIDTYPE_MAX;
          else if (upid < 0) {
                  type = PIDTYPE_PGID;
                  pid = find_get_pid(-upid);
          } else if (upid == 0) {
                  type = PIDTYPE_PGID;
                  pid = get_task_pid(current, PIDTYPE_PGID);
          } else /* upid > 0 */ {
                  type = PIDTYPE_PID;
                  pid = find_get_pid(upid);
          }
  
          wo.wo_type      = type;
          wo.wo_pid       = pid;
          wo.wo_flags     = options | WEXITED;
          wo.wo_info      = NULL;
          wo.wo_stat      = stat_addr;
          wo.wo_rusage    = ru;
          ret = do_wait(&wo);
          put_pid(pid);
  
          /* avoid REGPARM breakage on x86: */
          asmlinkage_protect(4, ret, upid, stat_addr, options, ru);
          return ret;
  }
  
  #ifdef __ARCH_WANT_SYS_WAITPID
  
  /*
   * sys_waitpid() remains for compatibility. waitpid() should be
   * implemented by calling sys_wait4() from libc.a.
   */
  SYSCALL_DEFINE3(waitpid, pid_t, pid, int __user *, stat_addr, int, options)
  {
          return sys_wait4(pid, stat_addr, options, NULL);
  }
  
  #endif

Cache object: 6c073923713a5ccb5c817dec8fdbb9be