[PATCH] kill altroot

[safe/jmp/linux-2.6] / 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/mnt_namespace.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/compat.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 <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 inline int task_detached(struct task_struct *p)
{
        return p->exit_signal == -1;
}

static void __unhash_process(struct task_struct *p)
{
        nr_threads--;
        detach_pid(p, PIDTYPE_PID);
        if (thread_group_leader(p)) {
                detach_pid(p, PIDTYPE_PGID);
                detach_pid(p, PIDTYPE_SID);

                list_del_rcu(&p->tasks);
                __get_cpu_var(process_counts)--;
        }
        list_del_rcu(&p->thread_group);
        list_del_init(&p->sibling);
}

/*
 * This function expects the tasklist_lock write-locked.
 */
static void __exit_signal(struct task_struct *tsk)
{
        struct signal_struct *sig = tsk->signal;
        struct sighand_struct *sighand;

        BUG_ON(!sig);
        BUG_ON(!atomic_read(&sig->count));

        sighand = rcu_dereference(tsk->sighand);
        spin_lock(&sighand->siglock);

        posix_cpu_timers_exit(tsk);
        if (atomic_dec_and_test(&sig->count))
                posix_cpu_timers_exit_group(tsk);
        else {
                /*
                 * If there is any task waiting for the group exit
                 * then notify it:
                 */
                if (sig->group_exit_task && atomic_read(&sig->count) == 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 = cputime_add(sig->utime, tsk->utime);
                sig->stime = cputime_add(sig->stime, tsk->stime);
                sig->gtime = cputime_add(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);
#ifdef CONFIG_TASK_XACCT
                sig->rchar += tsk->rchar;
                sig->wchar += tsk->wchar;
                sig->syscr += tsk->syscr;
                sig->syscw += tsk->syscw;
#endif /* CONFIG_TASK_XACCT */
#ifdef CONFIG_TASK_IO_ACCOUNTING
                sig->ioac.read_bytes += tsk->ioac.read_bytes;
                sig->ioac.write_bytes += tsk->ioac.write_bytes;
                sig->ioac.cancelled_write_bytes +=
                                        tsk->ioac.cancelled_write_bytes;
#endif /* CONFIG_TASK_IO_ACCOUNTING */
                sig->sum_sched_runtime += tsk->se.sum_exec_runtime;
                sig = NULL; /* Marker for below. */
        }

        __unhash_process(tsk);

        /*
         * Do this under ->siglock, we can race with another thread
         * doing sigqueue_free() if we have SIGQUEUE_PREALLOC signals.
         */
        flush_sigqueue(&tsk->pending);

        tsk->signal = NULL;
        tsk->sighand = NULL;
        spin_unlock(&sighand->siglock);

        __cleanup_sighand(sighand);
        clear_tsk_thread_flag(tsk,TIF_SIGPENDING);
        if (sig) {
                flush_sigqueue(&sig->shared_pending);
                taskstats_tgid_free(sig);
                __cleanup_signal(sig);
        }
}

static void delayed_put_task_struct(struct rcu_head *rhp)
{
        put_task_struct(container_of(rhp, struct task_struct, rcu));
}


void release_task(struct task_struct * p)
{
        struct task_struct *leader;
        int zap_leader;
repeat:
        tracehook_prepare_release_task(p);
        atomic_dec(&p->user->processes);
        proc_flush_task(p);
        write_lock_irq(&tasklist_lock);
        tracehook_finish_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) {
                BUG_ON(task_detached(leader));
                do_notify_parent(leader, leader->exit_signal);
                /*
                 * 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.
                 *
                 * do_notify_parent() will have marked it self-reaping in
                 * that case.
                 */
                zap_leader = task_detached(leader);

                /*
                 * This maintains the invariant that release_task()
                 * only runs on a task in EXIT_DEAD, just for sanity.
                 */
                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 int has_stopped_jobs(struct pid *pgrp)
{
        int retval = 0;
        struct task_struct *p;

        do_each_pid_task(pgrp, PIDTYPE_PGID, p) {
                if (!task_is_stopped(p))
                        continue;
                retval = 1;
                break;
        } while_each_pid_task(pgrp, PIDTYPE_PGID, p);
        return retval;
}

/*
 * 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);
        }
}

/**
 * reparent_to_kthreadd - Reparent the calling kernel thread to kthreadd
 *
 * If a kernel thread is launched as a result of a system call, or if
 * it ever exits, it should generally reparent itself to kthreadd so it
 * isn't in the way of other processes and is correctly cleaned up on exit.
 *
 * The various task state such as scheduling policy and priority may have
 * been inherited from a user process, so we reset them to sane values here.
 *
 * NOTE that reparent_to_kthreadd() gives the caller full capabilities.
 */
static void reparent_to_kthreadd(void)
{
        write_lock_irq(&tasklist_lock);

        ptrace_unlink(current);
        /* Reparent to init */
        current->real_parent = current->parent = kthreadd_task;
        list_move_tail(&current->sibling, &current->real_parent->children);

        /* Set the exit signal to SIGCHLD so we signal init on exit */
        current->exit_signal = SIGCHLD;

        if (task_nice(current) < 0)
                set_user_nice(current, 0);
        /* cpus_allowed? */
        /* rt_priority? */
        /* signals? */
        security_task_reparent_to_init(current);
        memcpy(current->signal->rlim, init_task.signal->rlim,
               sizeof(current->signal->rlim));
        atomic_inc(&(INIT_USER->__count));
        write_unlock_irq(&tasklist_lock);
        switch_uid(INIT_USER);
}

void __set_special_pids(struct pid *pid)
{
        struct task_struct *curr = current->group_leader;
        pid_t nr = pid_nr(pid);

        if (task_session(curr) != pid) {
                change_pid(curr, PIDTYPE_SID, pid);
                set_task_session(curr, nr);
        }
        if (task_pgrp(curr) != pid) {
                change_pid(curr, PIDTYPE_PGID, pid);
                set_task_pgrp(curr, nr);
        }
}

static void set_special_pids(struct pid *pid)
{
        write_lock_irq(&tasklist_lock);
        __set_special_pids(pid);
        write_unlock_irq(&tasklist_lock);
}

/*
 * Let kernel threads use this to say that they
 * allow a certain signal (since daemonize() will
 * have disabled all of them by default).
 */
int allow_signal(int sig)
{
        if (!valid_signal(sig) || sig < 1)
                return -EINVAL;

        spin_lock_irq(&current->sighand->siglock);
        sigdelset(&current->blocked, sig);
        if (!current->mm) {
                /* 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);

/*
 *      Put all the gunge required to become a kernel thread without
 *      attached user resources in one place where it belongs.
 */

void daemonize(const char *name, ...)
{
        va_list args;
        struct fs_struct *fs;
        sigset_t blocked;

        va_start(args, name);
        vsnprintf(current->comm, sizeof(current->comm), name, args);
        va_end(args);

        /*
         * If we were started as result of loading a module, close all of the
         * user space pages.  We don't need them, and if we didn't close them
         * they would be locked into memory.
         */
        exit_mm(current);
        /*
         * We don't want to have TIF_FREEZE set if the system-wide hibernation
         * or suspend transition begins right now.
         */
        current->flags |= (PF_NOFREEZE | PF_KTHREAD);

        if (current->nsproxy != &init_nsproxy) {
                get_nsproxy(&init_nsproxy);
                switch_task_namespaces(current, &init_nsproxy);
        }
        set_special_pids(&init_struct_pid);
        proc_clear_tty(current);

        /* Block and flush all signals */
        sigfillset(&blocked);
        sigprocmask(SIG_BLOCK, &blocked, NULL);
        flush_signals(current);

        /* Become as one with the init task */

        exit_fs(current);       /* current->fs->count--; */
        fs = init_task.fs;
        current->fs = fs;
        atomic_inc(&fs->count);

        exit_files(current);
        current->files = init_task.files;
        atomic_inc(&current->files->count);

        reparent_to_kthreadd();
}

EXPORT_SYMBOL(daemonize);

static void close_files(struct files_struct * files)
{
        int i, j;
        struct fdtable *fdt;

        j = 0;

        /*
         * It is safe to dereference the fd table without RCU or
         * ->file_lock because this is the last reference to the
         * files structure.
         */
        fdt = files_fdtable(files);
        for (;;) {
                unsigned long set;
                i = j * __NFDBITS;
                if (i >= fdt->max_fds)
                        break;
                set = fdt->open_fds->fds_bits[j++];
                while (set) {
                        if (set & 1) {
                                struct file * file = xchg(&fdt->fd[i], NULL);
                                if (file) {
                                        filp_close(file, files);
                                        cond_resched();
                                }
                        }
                        i++;
                        set >>= 1;
                }
        }
}

struct files_struct *get_files_struct(struct task_struct *task)
{
        struct files_struct *files;

        task_lock(task);
        files = task->files;
        if (files)
                atomic_inc(&files->count);
        task_unlock(task);

        return files;
}

void put_files_struct(struct files_struct *files)
{
        struct fdtable *fdt;

        if (atomic_dec_and_test(&files->count)) {
                close_files(files);
                /*
                 * Free the fd and fdset arrays if we expanded them.
                 * If the fdtable was embedded, pass files for freeing
                 * at the end of the RCU grace period. Otherwise,
                 * you can free files immediately.
                 */
                fdt = files_fdtable(files);
                if (fdt != &files->fdtab)
                        kmem_cache_free(files_cachep, files);
                free_fdtable(fdt);
        }
}

void reset_files_struct(struct files_struct *files)
{
        struct task_struct *tsk = current;
        struct files_struct *old;

        old = tsk->files;
        task_lock(tsk);
        tsk->files = files;
        task_unlock(tsk);
        put_files_struct(old);
}

void exit_files(struct task_struct *tsk)
{
        struct files_struct * files = tsk->files;

        if (files) {
                task_lock(tsk);
                tsk->files = NULL;
                task_unlock(tsk);
                put_files_struct(files);
        }
}

void put_fs_struct(struct fs_struct *fs)
{
        /* No need to hold fs->lock if we are killing it */
        if (atomic_dec_and_test(&fs->count)) {
                path_put(&fs->root);
                path_put(&fs->pwd);
                kmem_cache_free(fs_cachep, fs);
        }
}

void exit_fs(struct task_struct *tsk)
{
        struct fs_struct * fs = tsk->fs;

        if (fs) {
                task_lock(tsk);
                tsk->fs = NULL;
                task_unlock(tsk);
                put_fs_struct(fs);
        }
}

EXPORT_SYMBOL_GPL(exit_fs);

#ifdef CONFIG_MM_OWNER
/*
 * Task p is exiting and it owned mm, lets find a new owner for it
 */
static inline int
mm_need_new_owner(struct mm_struct *mm, struct task_struct *p)
{
        /*
         * If there are other users of the mm and the owner (us) is exiting
         * we need to find a new owner to take on the responsibility.
         */
        if (!mm)
                return 0;
        if (atomic_read(&mm->mm_users) <= 1)
                return 0;
        if (mm->owner != p)
                return 0;
        return 1;
}

void mm_update_next_owner(struct mm_struct *mm)
{
        struct task_struct *c, *g, *p = current;

retry:
        if (!mm_need_new_owner(mm, p))
                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->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);
        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;
        }
        cgroup_mm_owner_callbacks(mm->owner, c);
        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;
        /*
         * 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);
        /* We don't want this task to be frozen prematurely */
        clear_freeze_flag(tsk);
        task_unlock(tsk);
        mm_update_next_owner(mm);
        mmput(mm);
}

/*
 * Return nonzero if @parent's children should reap themselves.
 *
 * Called with write_lock_irq(&tasklist_lock) held.
 */
static int ignoring_children(struct task_struct *parent)
{
        int ret;
        struct sighand_struct *psig = parent->sighand;
        unsigned long flags;
        spin_lock_irqsave(&psig->siglock, flags);
        ret = (psig->action[SIGCHLD-1].sa.sa_handler == SIG_IGN ||
               (psig->action[SIGCHLD-1].sa.sa_flags & SA_NOCLDWAIT));
        spin_unlock_irqrestore(&psig->siglock, flags);
        return ret;
}

/*
 * Detach all tasks we were using ptrace on.
 * Any that need to be release_task'd are put on the @dead list.
 *
 * Called with write_lock(&tasklist_lock) held.
 */
static void ptrace_exit(struct task_struct *parent, struct list_head *dead)
{
        struct task_struct *p, *n;
        int ign = -1;

        list_for_each_entry_safe(p, n, &parent->ptraced, ptrace_entry) {
                __ptrace_unlink(p);

                if (p->exit_state != EXIT_ZOMBIE)
                        continue;

                /*
                 * If it's a zombie, our attachedness prevented normal
                 * parent notification or self-reaping.  Do notification
                 * now if it would have happened earlier.  If it should
                 * reap itself, add it to the @dead list.  We can't call
                 * release_task() here because we already hold tasklist_lock.
                 *
                 * If it's our own child, there is no notification to do.
                 * But if our normal children self-reap, then this child
                 * was prevented by ptrace and we must reap it now.
                 */
                if (!task_detached(p) && thread_group_empty(p)) {
                        if (!same_thread_group(p->real_parent, parent))
                                do_notify_parent(p, p->exit_signal);
                        else {
                                if (ign < 0)
                                        ign = ignoring_children(parent);
                                if (ign)
                                        p->exit_signal = -1;
                        }
                }

                if (task_detached(p)) {
                        /*
                         * Mark it as in the process of being reaped.
                         */
                        p->exit_state = EXIT_DEAD;
                        list_add(&p->ptrace_entry, dead);
                }
        }
}

/*
 * Finish up exit-time ptrace cleanup.
 *
 * Called without locks.
 */
static void ptrace_exit_finish(struct task_struct *parent,
                               struct list_head *dead)
{
        struct task_struct *p, *n;

        BUG_ON(!list_empty(&parent->ptraced));

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

static void reparent_thread(struct task_struct *p, struct task_struct *father)
{
        if (p->pdeath_signal)
                /* We already hold the tasklist_lock here.  */
                group_send_sig_info(p->pdeath_signal, SEND_SIG_NOINFO, p);

        list_move_tail(&p->sibling, &p->real_parent->children);

        /* If this is a threaded reparent there is no need to
         * notify anyone anything has happened.
         */
        if (same_thread_group(p->real_parent, father))
                return;

        /* We don't want people slaying init.  */
        if (!task_detached(p))
                p->exit_signal = SIGCHLD;

        /* If we'd notified the old parent about this child's death,
         * also notify the new parent.
         */
        if (!ptrace_reparented(p) &&
            p->exit_state == EXIT_ZOMBIE &&
            !task_detached(p) && thread_group_empty(p))
                do_notify_parent(p, p->exit_signal);

        kill_orphaned_pgrp(p, father);
}

/*
 * When we die, we re-parent all our children.
 * Try to give them to another thread in our thread
 * group, and if no such member exists, give it to
 * the child reaper process (ie "init") in our pid
 * space.
 */
static void forget_original_parent(struct task_struct *father)
{
        struct task_struct *p, *n, *reaper = father;
        LIST_HEAD(ptrace_dead);

        write_lock_irq(&tasklist_lock);

        /*
         * First clean up ptrace if we were using it.
         */
        ptrace_exit(father, &ptrace_dead);

        do {
                reaper = next_thread(reaper);
                if (reaper == father) {
                        reaper = task_child_reaper(father);
                        break;
                }
        } while (reaper->flags & PF_EXITING);

        list_for_each_entry_safe(p, n, &father->children, sibling) {
                p->real_parent = reaper;
                if (p->parent == father) {
                        BUG_ON(p->ptrace);
                        p->parent = p->real_parent;
                }
                reparent_thread(p, father);
        }

        write_unlock_irq(&tasklist_lock);
        BUG_ON(!list_empty(&father->children));

        ptrace_exit_finish(father, &ptrace_dead);
}

/*
 * 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)
{
        int signal;
        void *cookie;

        /*
         * 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);

        /* Let father know we died
         *
         * Thread signals are configurable, but you aren't going to use
         * that to send signals to arbitary processes.
         * That stops right now.
         *
         * If the parent exec id doesn't match the exec id we saved
         * when we started then we know the parent has changed security
         * domain.
         *
         * If our self_exec id doesn't match our parent_exec_id then
         * we have changed execution domain as these two values started
         * the same after a fork.
         */
        if (tsk->exit_signal != SIGCHLD && !task_detached(tsk) &&
            (tsk->parent_exec_id != tsk->real_parent->self_exec_id ||
             tsk->self_exec_id != tsk->parent_exec_id) &&
            !capable(CAP_KILL))
                tsk->exit_signal = SIGCHLD;

        signal = tracehook_notify_death(tsk, &cookie, group_dead);
        if (signal > 0)
                signal = do_notify_parent(tsk, signal);

        tsk->exit_state = signal < 0 ? EXIT_DEAD : EXIT_ZOMBIE;

        /* mt-exec, de_thread() is waiting for us */
        if (thread_group_leader(tsk) &&
            tsk->signal->notify_count < 0 &&
            tsk->signal->group_exit_task)
                wake_up_process(tsk->signal->group_exit_task);

        write_unlock_irq(&tasklist_lock);

        tracehook_report_death(tsk, signal, cookie, group_dead);

        /* If the process is dead, release it - nobody will wait for it */
        if (signal < 0)
                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 *n = end_of_stack(current);
        unsigned long free;

        while (*n == 0)
                n++;
        free = (unsigned long)n - (unsigned long)end_of_stack(current);

        if (free >= lowest_to_date)
                return;

        spin_lock(&low_water_lock);
        if (free < lowest_to_date) {
                printk(KERN_WARNING "%s used greatest stack depth: %lu bytes "
                                "left\n",
                                current->comm, free);
                lowest_to_date = free;
        }
        spin_unlock(&low_water_lock);
}
#else
static inline void check_stack_usage(void) {}
#endif

static inline void exit_child_reaper(struct task_struct *tsk)
{
        if (likely(tsk->group_leader != task_child_reaper(tsk)))
                return;

        if (tsk->nsproxy->pid_ns == &init_pid_ns)
                panic("Attempted to kill init!");

        /*
         * @tsk is the last thread in the 'cgroup-init' and is exiting.
         * Terminate all remaining processes in the namespace and reap them
         * before exiting @tsk.
         *
         * Note that @tsk (last thread of cgroup-init) may not necessarily
         * be the child-reaper (i.e main thread of cgroup-init) of the
         * namespace i.e the child_reaper may have already exited.
         *
         * Even after a child_reaper exits, we let it inherit orphaned children,
         * because, pid_ns->child_reaper remains valid as long as there is
         * at least one living sub-thread in the cgroup init.

         * This living sub-thread of the cgroup-init will be notified when
         * a child inherited by the 'child-reaper' exits (do_notify_parent()
         * uses __group_send_sig_info()). Further, when reaping child processes,
         * do_wait() iterates over children of all living sub threads.

         * i.e even though 'child_reaper' thread is listed as the parent of the
         * orphaned children, any living sub-thread in the cgroup-init can
         * perform the role of the child_reaper.
         */
        zap_pid_ns_processes(tsk->nsproxy->pid_ns);
}

NORET_TYPE void do_exit(long code)
{
        struct task_struct *tsk = current;
        int group_dead;

        profile_task_exit(tsk);

        WARN_ON(atomic_read(&tsk->fs_excl));

        if (unlikely(in_interrupt()))
                panic("Aiee, killing interrupt handler!");
        if (unlikely(!tsk->pid))
                panic("Attempted to kill the idle task!");

        tracehook_report_exit(&code);

        /*
         * 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;
                if (tsk->io_context)
                        exit_io_context();
                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();
        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);
        if (tsk->mm) {
                update_hiwater_rss(tsk->mm);
                update_hiwater_vm(tsk->mm);
        }
        group_dead = atomic_dec_and_test(&tsk->signal->live);
        if (group_dead) {
                exit_child_reaper(tsk);
                hrtimer_cancel(&tsk->signal->real_timer);
                exit_itimers(tsk->signal);
        }
        acct_collect(code, group_dead);
#ifdef CONFIG_FUTEX
        if (unlikely(tsk->robust_list))
                exit_robust_list(tsk);
#ifdef CONFIG_COMPAT
        if (unlikely(tsk->compat_robust_list))
                compat_exit_robust_list(tsk);
#endif
#endif
        if (group_dead)
                tty_audit_exit();
        if (unlikely(tsk->audit_context))
                audit_free(tsk);

        tsk->exit_code = code;
        taskstats_exit(tsk, group_dead);

        exit_mm(tsk);

        if (group_dead)
                acct_process();
        exit_sem(tsk);
        exit_files(tsk);
        exit_fs(tsk);
        check_stack_usage();
        exit_thread();
        cgroup_exit(tsk, 1);
        exit_keys(tsk);

        if (group_dead && tsk->signal->leader)
                disassociate_ctty(1);

        module_put(task_thread_info(tsk)->exec_domain->module);
        if (tsk->binfmt)
                module_put(tsk->binfmt->module);

        proc_exit_connector(tsk);
        exit_notify(tsk, group_dead);
#ifdef CONFIG_NUMA
        mpol_put(tsk->mempolicy);
        tsk->mempolicy = NULL;
#endif
#ifdef CONFIG_FUTEX
        /*
         * This must happen late, after the PID is not
         * hashed anymore:
         */
        if (unlikely(!list_empty(&tsk->pi_state_list)))
                exit_pi_state_list(tsk);
        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();

        if (tsk->splice_pipe)
                __free_pipe_info(tsk->splice_pipe);

        preempt_disable();
        /* causes final put_task_struct in finish_task_switch(). */
        tsk->state = TASK_DEAD;

        schedule();
        BUG();
        /* Avoid "noreturn function does return".  */
        for (;;)
                cpu_relax();    /* For when BUG is null */
}

EXPORT_SYMBOL_GPL(do_exit);

NORET_TYPE void complete_and_exit(struct completion *comp, long code)
{
        if (comp)
                complete(comp);

        do_exit(code);
}

EXPORT_SYMBOL(complete_and_exit);

asmlinkage long sys_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).
 */
NORET_TYPE 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.
 */
asmlinkage void sys_exit_group(int error_code)
{
        do_group_exit((error_code & 0xff) << 8);
}

static struct pid *task_pid_type(struct task_struct *task, enum pid_type type)
{
        struct pid *pid = NULL;
        if (type == PIDTYPE_PID)
                pid = task->pids[type].pid;
        else if (type < PIDTYPE_MAX)
                pid = task->group_leader->pids[type].pid;
        return pid;
}

static int eligible_child(enum pid_type type, struct pid *pid, int options,
                          struct task_struct *p)
{
        int err;

        if (type < PIDTYPE_MAX) {
                if (task_pid_type(p, type) != pid)
                        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) ^ ((options & __WCLONE) != 0))
            && !(options & __WALL))
                return 0;

        err = security_task_wait(p);
        if (err)
                return err;

        return 1;
}

static int wait_noreap_copyout(struct task_struct *p, pid_t pid, uid_t uid,
                               int why, int status,
                               struct siginfo __user *infop,
                               struct rusage __user *rusagep)
{
        int retval = rusagep ? getrusage(p, RUSAGE_BOTH, rusagep) : 0;

        put_task_struct(p);
        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 task_struct *p, int options,
                            struct siginfo __user *infop,
                            int __user *stat_addr, struct rusage __user *ru)
{
        unsigned long state;
        int retval, status, traced;
        pid_t pid = task_pid_vnr(p);

        if (!likely(options & WEXITED))
                return 0;

        if (unlikely(options & WNOWAIT)) {
                uid_t uid = p->uid;
                int exit_code = p->exit_code;
                int why, status;

                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(p, pid, uid, why,
                                           status, infop, ru);
        }

        /*
         * 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);

        if (likely(!traced)) {
                struct signal_struct *psig;
                struct signal_struct *sig;

                /*
                 * 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 p->parent->signal fields,
                 * as other threads in the parent group can be right
                 * here reaping other children at the same time.
                 */
                spin_lock_irq(&p->parent->sighand->siglock);
                psig = p->parent->signal;
                sig = p->signal;
                psig->cutime =
                        cputime_add(psig->cutime,
                        cputime_add(p->utime,
                        cputime_add(sig->utime,
                                    sig->cutime)));
                psig->cstime =
                        cputime_add(psig->cstime,
                        cputime_add(p->stime,
                        cputime_add(sig->stime,
                                    sig->cstime)));
                psig->cgtime =
                        cputime_add(psig->cgtime,
                        cputime_add(p->gtime,
                        cputime_add(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;
#ifdef CONFIG_TASK_XACCT
                psig->rchar += p->rchar + sig->rchar;
                psig->wchar += p->wchar + sig->wchar;
                psig->syscr += p->syscr + sig->syscr;
                psig->syscw += p->syscw + sig->syscw;
#endif /* CONFIG_TASK_XACCT */
#ifdef CONFIG_TASK_IO_ACCOUNTING
                psig->ioac.read_bytes +=
                        p->ioac.read_bytes + sig->ioac.read_bytes;
                psig->ioac.write_bytes +=
                        p->ioac.write_bytes + sig->ioac.write_bytes;
                psig->ioac.cancelled_write_bytes +=
                                p->ioac.cancelled_write_bytes +
                                sig->ioac.cancelled_write_bytes;
#endif /* CONFIG_TASK_IO_ACCOUNTING */
                spin_unlock_irq(&p->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 = ru ? getrusage(p, RUSAGE_BOTH, ru) : 0;
        status = (p->signal->flags & SIGNAL_GROUP_EXIT)
                ? p->signal->group_exit_code : p->exit_code;
        if (!retval && stat_addr)
                retval = put_user(status, stat_addr);
        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(p->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 detached task, notify the parent.
                 * If it's still not detached after that, don't release
                 * it now.
                 */
                if (!task_detached(p)) {
                        do_notify_parent(p, p->exit_signal);
                        if (!task_detached(p)) {
                                p->exit_state = EXIT_ZOMBIE;
                                p = NULL;
                        }
                }
                write_unlock_irq(&tasklist_lock);
        }
        if (p != NULL)
                release_task(p);

        return retval;
}

/*
 * Handle sys_wait4 work for one task in state TASK_STOPPED.  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_stopped(int ptrace, struct task_struct *p,
                             int options, struct siginfo __user *infop,
                             int __user *stat_addr, struct rusage __user *ru)
{
        int retval, exit_code, why;
        uid_t uid = 0; /* unneeded, required by compiler */
        pid_t pid;

        if (!(options & WUNTRACED))
                return 0;

        exit_code = 0;
        spin_lock_irq(&p->sighand->siglock);

        if (unlikely(!task_is_stopped_or_traced(p)))
                goto unlock_sig;

        if (!ptrace && p->signal->group_stop_count > 0)
                /*
                 * A group stop is in progress and this is the group leader.
                 * We won't report until all threads have stopped.
                 */
                goto unlock_sig;

        exit_code = p->exit_code;
        if (!exit_code)
                goto unlock_sig;

        if (!unlikely(options & WNOWAIT))
                p->exit_code = 0;

        uid = p->uid;
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(options & WNOWAIT))
                return wait_noreap_copyout(p, pid, uid,
                                           why, exit_code,
                                           infop, ru);

        retval = ru ? getrusage(p, RUSAGE_BOTH, ru) : 0;
        if (!retval && stat_addr)
                retval = put_user((exit_code << 8) | 0x7f, stat_addr);
        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 task_struct *p, int options,
                               struct siginfo __user *infop,
                               int __user *stat_addr, struct rusage __user *ru)
{
        int retval;
        pid_t pid;
        uid_t uid;

        if (!unlikely(options & 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(options & WNOWAIT))
                p->signal->flags &= ~SIGNAL_STOP_CONTINUED;
        spin_unlock_irq(&p->sighand->siglock);

        pid = task_pid_vnr(p);
        uid = p->uid;
        get_task_struct(p);
        read_unlock(&tasklist_lock);

        if (!infop) {
                retval = ru ? getrusage(p, RUSAGE_BOTH, ru) : 0;
                put_task_struct(p);
                if (!retval && stat_addr)
                        retval = put_user(0xffff, stat_addr);
                if (!retval)
                        retval = pid;
        } else {
                retval = wait_noreap_copyout(p, pid, uid,
                                             CLD_CONTINUED, SIGCONT,
                                             infop, ru);
                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 task_struct *parent, int ptrace,
                              struct task_struct *p, int *notask_error,
                              enum pid_type type, struct pid *pid, int options,
                              struct siginfo __user *infop,
                              int __user *stat_addr, struct rusage __user *ru)
{
        int ret = eligible_child(type, pid, options, p);
        if (!ret)
                return ret;

        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 (*notask_error)
                        *notask_error = ret;
        }

        if (likely(!ptrace) && unlikely(p->ptrace)) {
                /*
                 * This child is hidden by ptrace.
                 * We aren't allowed to see it now, but eventually we will.
                 */
                *notask_error = 0;
                return 0;
        }

        if (p->exit_state == EXIT_DEAD)
                return 0;

        /*
         * We don't reap group leaders with subthreads.
         */
        if (p->exit_state == EXIT_ZOMBIE && !delay_group_leader(p))
                return wait_task_zombie(p, options, infop, stat_addr, ru);

        /*
         * It's stopped or running now, so it might
         * later continue, exit, or stop again.
         */
        *notask_error = 0;

        if (task_is_stopped_or_traced(p))
                return wait_task_stopped(ptrace, p, options,
                                         infop, stat_addr, ru);

        return wait_task_continued(p, options, infop, stat_addr, ru);
}

/*
 * 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 task_struct *tsk, int *notask_error,
                          enum pid_type type, struct pid *pid, int options,
                          struct siginfo __user *infop, int __user *stat_addr,
                          struct rusage __user *ru)
{
        struct task_struct *p;

        list_for_each_entry(p, &tsk->children, sibling) {
                /*
                 * Do not consider detached threads.
                 */
                if (!task_detached(p)) {
                        int ret = wait_consider_task(tsk, 0, p, notask_error,
                                                     type, pid, options,
                                                     infop, stat_addr, ru);
                        if (ret)
                                return ret;
                }
        }

        return 0;
}

static int ptrace_do_wait(struct task_struct *tsk, int *notask_error,
                          enum pid_type type, struct pid *pid, int options,
                          struct siginfo __user *infop, int __user *stat_addr,
                          struct rusage __user *ru)
{
        struct task_struct *p;

        /*
         * Traditionally we see ptrace'd stopped tasks regardless of options.
         */
        options |= WUNTRACED;

        list_for_each_entry(p, &tsk->ptraced, ptrace_entry) {
                int ret = wait_consider_task(tsk, 1, p, notask_error,
                                             type, pid, options,
                                             infop, stat_addr, ru);
                if (ret)
                        return ret;
        }

        return 0;
}

static long do_wait(enum pid_type type, struct pid *pid, int options,
                    struct siginfo __user *infop, int __user *stat_addr,
                    struct rusage __user *ru)
{
        DECLARE_WAITQUEUE(wait, current);
        struct task_struct *tsk;
        int retval;

        add_wait_queue(&current->signal->wait_chldexit,&wait);
repeat:
        /*
         * If there is nothing that can match our critiera just get out.
         * We will clear @retval to zero if we see any child that might later
         * match our criteria, even if we are not able to reap it yet.
         */
        retval = -ECHILD;
        if ((type < PIDTYPE_MAX) && (!pid || hlist_empty(&pid->tasks[type])))
                goto end;

        current->state = TASK_INTERRUPTIBLE;
        read_lock(&tasklist_lock);
        tsk = current;
        do {
                int tsk_result = do_wait_thread(tsk, &retval,
                                                type, pid, options,
                                                infop, stat_addr, ru);
                if (!tsk_result)
                        tsk_result = ptrace_do_wait(tsk, &retval,
                                                    type, pid, options,
                                                    infop, stat_addr, ru);
                if (tsk_result) {
                        /*
                         * tasklist_lock is unlocked and we have a final result.
                         */
                        retval = tsk_result;
                        goto end;
                }

                if (options & __WNOTHREAD)
                        break;
                tsk = next_thread(tsk);
                BUG_ON(tsk->signal != current->signal);
        } while (tsk != current);
        read_unlock(&tasklist_lock);

        if (!retval && !(options & WNOHANG)) {
                retval = -ERESTARTSYS;
                if (!signal_pending(current)) {
                        schedule();
                        goto repeat;
                }
        }

end:
        current->state = TASK_RUNNING;
        remove_wait_queue(&current->signal->wait_chldexit,&wait);
        if (infop) {
                if (retval > 0)
                        retval = 0;
                else {
                        /*
                         * For a WNOHANG return, clear out all the fields
                         * we would set so the user can easily tell the
                         * difference.
                         */
                        if (!retval)
                                retval = put_user(0, &infop->si_signo);
                        if (!retval)
                                retval = put_user(0, &infop->si_errno);
                        if (!retval)
                                retval = put_user(0, &infop->si_code);
                        if (!retval)
                                retval = put_user(0, &infop->si_pid);
                        if (!retval)
                                retval = put_user(0, &infop->si_uid);
                        if (!retval)
                                retval = put_user(0, &infop->si_status);
                }
        }
        return retval;
}

asmlinkage long sys_waitid(int which, pid_t upid,
                           struct siginfo __user *infop, int options,
                           struct rusage __user *ru)
{
        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);
        ret = do_wait(type, pid, options, infop, NULL, ru);
        put_pid(pid);

        /* avoid REGPARM breakage on x86: */
        asmlinkage_protect(5, ret, which, upid, infop, options, ru);
        return ret;
}

asmlinkage long sys_wait4(pid_t upid, int __user *stat_addr,
                          int options, struct rusage __user *ru)
{
        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_pid(task_pgrp(current));
        } else /* upid > 0 */ {
                type = PIDTYPE_PID;
                pid = find_get_pid(upid);
        }

        ret = do_wait(type, pid, options | WEXITED, NULL, stat_addr, ru);
        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.
 */
asmlinkage long sys_waitpid(pid_t pid, int __user *stat_addr, int options)
{
        return sys_wait4(pid, stat_addr, options, NULL);
}

#endif