More unused junk.

[linux-2.6/linux-mips.git] / kernel / exit.c

/*
 *  linux/kernel/exit.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

#include <linux/config.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/interrupt.h>
#include <linux/smp_lock.h>
#include <linux/module.h>
#include <linux/completion.h>
#include <linux/personality.h>
#include <linux/tty.h>
#include <linux/namespace.h>
#include <linux/security.h>
#include <linux/acct.h>
#include <linux/file.h>
#include <linux/binfmts.h>
#include <linux/ptrace.h>
#include <linux/profile.h>
#include <linux/mount.h>
#include <linux/proc_fs.h>

#include <asm/uaccess.h>
#include <asm/pgtable.h>
#include <asm/mmu_context.h>

extern void sem_exit (void);
extern struct task_struct *child_reaper;

int getrusage(struct task_struct *, int, struct rusage *);

static void __unhash_process(struct task_struct *p)
{
        nr_threads--;
        detach_pid(p, PIDTYPE_PID);
        detach_pid(p, PIDTYPE_TGID);
        if (thread_group_leader(p)) {
                detach_pid(p, PIDTYPE_PGID);
                detach_pid(p, PIDTYPE_SID);
                if (p->pid)
                        per_cpu(process_counts, smp_processor_id())--;
        }

        REMOVE_LINKS(p);
}

void release_task(struct task_struct * p)
{
        task_t *leader;
        struct dentry *proc_dentry;
 
        BUG_ON(p->state < TASK_ZOMBIE);
 
        atomic_dec(&p->user->processes);
        spin_lock(&p->proc_lock);
        proc_dentry = proc_pid_unhash(p);
        write_lock_irq(&tasklist_lock);
        if (unlikely(p->ptrace))
                __ptrace_unlink(p);
        BUG_ON(!list_empty(&p->ptrace_list) || !list_empty(&p->ptrace_children));
        __exit_signal(p);
        __exit_sighand(p);
        __unhash_process(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.)
         */
        leader = p->group_leader;
        if (leader != p && thread_group_empty(leader) &&
                    leader->state == TASK_ZOMBIE && leader->exit_signal != -1)
                do_notify_parent(leader, leader->exit_signal);

        p->parent->cutime += p->utime + p->cutime;
        p->parent->cstime += p->stime + p->cstime;
        p->parent->cmin_flt += p->min_flt + p->cmin_flt;
        p->parent->cmaj_flt += p->maj_flt + p->cmaj_flt;
        p->parent->cnswap += p->nswap + p->cnswap;
        sched_exit(p);
        write_unlock_irq(&tasklist_lock);
        spin_unlock(&p->proc_lock);
        proc_pid_flush(proc_dentry);
        release_thread(p);
        put_task_struct(p);
}

/* we are using it only for SMP init */

void unhash_process(struct task_struct *p)
{
        struct dentry *proc_dentry;

        spin_lock(&p->proc_lock);
        proc_dentry = proc_pid_unhash(p);
        write_lock_irq(&tasklist_lock);
        __unhash_process(p);
        write_unlock_irq(&tasklist_lock);
        spin_unlock(&p->proc_lock);
        proc_pid_flush(proc_dentry);
}

/*
 * 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...
 */
int session_of_pgrp(int pgrp)
{
        struct task_struct *p;
        struct list_head *l;
        struct pid *pid;
        int sid = -1;

        read_lock(&tasklist_lock);
        for_each_task_pid(pgrp, PIDTYPE_PGID, p, l, pid)
                if (p->session > 0) {
                        sid = p->session;
                        goto out;
                }
        p = find_task_by_pid(pgrp);
        if (p)
                sid = p->session;
out:
        read_unlock(&tasklist_lock);
        
        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(int pgrp, task_t *ignored_task)
{
        struct task_struct *p;
        struct list_head *l;
        struct pid *pid;
        int ret = 1;

        for_each_task_pid(pgrp, PIDTYPE_PGID, p, l, pid) {
                if (p == ignored_task
                                || p->state >= TASK_ZOMBIE 
                                || p->real_parent->pid == 1)
                        continue;
                if (p->real_parent->pgrp != pgrp
                            && p->real_parent->session == p->session) {
                        ret = 0;
                        break;
                }
        }
        return ret;     /* (sighing) "Often!" */
}

int is_orphaned_pgrp(int pgrp)
{
        int retval;

        read_lock(&tasklist_lock);
        retval = will_become_orphaned_pgrp(pgrp, NULL);
        read_unlock(&tasklist_lock);

        return retval;
}

static inline int has_stopped_jobs(int pgrp)
{
        int retval = 0;
        struct task_struct *p;
        struct list_head *l;
        struct pid *pid;

        for_each_task_pid(pgrp, PIDTYPE_PGID, p, l, pid) {
                if (p->state != TASK_STOPPED)
                        continue;

                /* If p is stopped by a debugger on a signal that won't
                   stop it, then don't count p as stopped.  This isn't
                   perfect but it's a good approximation.  */
                if (unlikely (p->ptrace)
                    && p->exit_code != SIGSTOP
                    && p->exit_code != SIGTSTP
                    && p->exit_code != SIGTTOU
                    && p->exit_code != SIGTTIN)
                        continue;

                retval = 1;
                break;
        }
        return retval;
}

/**
 * reparent_to_init() - Reparent the calling kernel thread to the init task.
 *
 * If a kernel thread is launched as a result of a system call, or if
 * it ever exits, it should generally reparent itself to init so that
 * it 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_init() gives the caller full capabilities.
 */
void reparent_to_init(void)
{
        write_lock_irq(&tasklist_lock);

        ptrace_unlink(current);
        /* Reparent to init */
        REMOVE_LINKS(current);
        current->parent = child_reaper;
        current->real_parent = child_reaper;
        SET_LINKS(current);

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

        if ((current->policy == SCHED_NORMAL) && (task_nice(current) < 0))
                set_user_nice(current, 0);
        /* cpus_allowed? */
        /* rt_priority? */
        /* signals? */
        security_task_reparent_to_init(current);
        memcpy(current->rlim, init_task.rlim, sizeof(*(current->rlim)));
        switch_uid(INIT_USER);

        write_unlock_irq(&tasklist_lock);
}

void __set_special_pids(pid_t session, pid_t pgrp)
{
        struct task_struct *curr = current;

        if (curr->session != session) {
                detach_pid(curr, PIDTYPE_SID);
                curr->session = session;
                attach_pid(curr, PIDTYPE_SID, session);
        }
        if (curr->pgrp != pgrp) {
                detach_pid(curr, PIDTYPE_PGID);
                curr->pgrp = pgrp;
                attach_pid(curr, PIDTYPE_PGID, pgrp);
        }
}

void set_special_pids(pid_t session, pid_t pgrp)
{
        write_lock_irq(&tasklist_lock);
        __set_special_pids(session, pgrp);
        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 (sig < 1 || sig > _NSIG)
                return -EINVAL;

        spin_lock_irq(&current->sighand->siglock);
        sigdelset(&current->blocked, sig);
        recalc_sigpending();
        spin_unlock_irq(&current->sighand->siglock);
        return 0;
}

EXPORT_SYMBOL(allow_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);

        set_special_pids(1, 1);
        current->tty = NULL;

        /* 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_init();
}

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

        j = 0;
        for (;;) {
                unsigned long set;
                i = j * __NFDBITS;
                if (i >= files->max_fdset || i >= files->max_fds)
                        break;
                set = files->open_fds->fds_bits[j++];
                while (set) {
                        if (set & 1) {
                                struct file * file = xchg(&files->fd[i], NULL);
                                if (file)
                                        filp_close(file, files);
                        }
                        i++;
                        set >>= 1;
                }
        }
}

void put_files_struct(struct files_struct *files)
{
        if (atomic_dec_and_test(&files->count)) {
                close_files(files);
                /*
                 * Free the fd and fdset arrays if we expanded them.
                 */
                if (files->fd != &files->fd_array[0])
                        free_fd_array(files->fd, files->max_fds);
                if (files->max_fdset > __FD_SETSIZE) {
                        free_fdset(files->open_fds, files->max_fdset);
                        free_fdset(files->close_on_exec, files->max_fdset);
                }
                kmem_cache_free(files_cachep, files);
        }
}

static inline 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 exit_files(struct task_struct *tsk)
{
        __exit_files(tsk);
}

static inline 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)) {
                dput(fs->root);
                mntput(fs->rootmnt);
                dput(fs->pwd);
                mntput(fs->pwdmnt);
                if (fs->altroot) {
                        dput(fs->altroot);
                        mntput(fs->altrootmnt);
                }
                kmem_cache_free(fs_cachep, fs);
        }
}

void put_fs_struct(struct fs_struct *fs)
{
        __put_fs_struct(fs);
}

static inline 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);
        }
}

void exit_fs(struct task_struct *tsk)
{
        __exit_fs(tsk);
}

/*
 * Turn us into a lazy TLB process if we
 * aren't already..
 */
static inline void __exit_mm(struct task_struct * tsk)
{
        struct mm_struct *mm = tsk->mm;

        mm_release(tsk, mm);
        if (!mm)
                return;
        /*
         * Serialize with any possible pending coredump:
         */
        if (mm->core_waiters) {
                down_write(&mm->mmap_sem);
                if (!--mm->core_waiters)
                        complete(mm->core_startup_done);
                up_write(&mm->mmap_sem);

                wait_for_completion(&mm->core_done);
        }
        atomic_inc(&mm->mm_count);
        if (mm != tsk->active_mm) BUG();
        /* more a memory barrier than a real lock */
        task_lock(tsk);
        tsk->mm = NULL;
        enter_lazy_tlb(mm, current, smp_processor_id());
        task_unlock(tsk);
        mmput(mm);
}

void exit_mm(struct task_struct *tsk)
{
        __exit_mm(tsk);
}

static inline void choose_new_parent(task_t *p, task_t *reaper, task_t *child_reaper)
{
        /*
         * Make sure we're not reparenting to ourselves and that
         * the parent is not a zombie.
         */
        if (p == reaper || reaper->state >= TASK_ZOMBIE)
                p->real_parent = child_reaper;
        else
                p->real_parent = reaper;
        if (p->parent == p->real_parent)
                BUG();
}

static inline void reparent_thread(task_t *p, task_t *father, int traced)
{
        /* We don't want people slaying init.  */
        if (p->exit_signal != -1)
                p->exit_signal = SIGCHLD;
        p->self_exec_id++;

        if (p->pdeath_signal)
                send_group_sig_info(p->pdeath_signal, 0, p);

        /* Move the child from its dying parent to the new one.  */
        if (unlikely(traced)) {
                /* Preserve ptrace links if someone else is tracing this child.  */
                list_del_init(&p->ptrace_list);
                if (p->parent != p->real_parent)
                        list_add(&p->ptrace_list, &p->real_parent->ptrace_children);
        } else {
                /* If this child is being traced, then we're the one tracing it
                 * anyway, so let go of it.
                 */
                p->ptrace = 0;
                list_del_init(&p->sibling);
                p->parent = p->real_parent;
                list_add_tail(&p->sibling, &p->parent->children);

                /* If we'd notified the old parent about this child's death,
                 * also notify the new parent.
                 */
                if (p->state == TASK_ZOMBIE && p->exit_signal != -1)
                        do_notify_parent(p, p->exit_signal);
        }

        /*
         * process group orphan check
         * Case ii: Our child is in a different pgrp
         * than we are, and it was the only connection
         * outside, so the child pgrp is now orphaned.
         */
        if ((p->pgrp != father->pgrp) &&
            (p->session == father->session)) {
                int pgrp = p->pgrp;

                if (will_become_orphaned_pgrp(pgrp, NULL) && has_stopped_jobs(pgrp)) {
                        __kill_pg_info(SIGHUP, (void *)1, pgrp);
                        __kill_pg_info(SIGCONT, (void *)1, pgrp);
                }
        }
}

/*
 * 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 global child reaper process (ie "init")
 */
static inline void forget_original_parent(struct task_struct * father)
{
        struct task_struct *p, *reaper = father;
        struct list_head *_p, *_n;

        reaper = father->group_leader;
        if (reaper == father)
                reaper = child_reaper;

        /*
         * There are only two places where our children can be:
         *
         * - in our child list
         * - in our ptraced child list
         *
         * Search them and reparent children.
         */
        list_for_each_safe(_p, _n, &father->children) {
                p = list_entry(_p,struct task_struct,sibling);
                if (father == p->real_parent) {
                        choose_new_parent(p, reaper, child_reaper);
                        reparent_thread(p, father, 0);
                } else {
                        ptrace_unlink (p);
                        if (p->state == TASK_ZOMBIE && p->exit_signal != -1)
                                do_notify_parent(p, p->exit_signal);
                }
        }
        list_for_each_safe(_p, _n, &father->ptrace_children) {
                p = list_entry(_p,struct task_struct,ptrace_list);
                choose_new_parent(p, reaper, child_reaper);
                reparent_thread(p, father, 1);
        }
}

/*
 * Send signals to all our closest relatives so that they know
 * to properly mourn us..
 */
static void exit_notify(struct task_struct *tsk)
{
        struct task_struct *t;

        if (signal_pending(tsk) && !tsk->signal->group_exit
            && !thread_group_empty(tsk)) {
                /*
                 * This occurs when there was a race between our exit
                 * syscall and a group signal choosing us as the one to
                 * wake up.  It could be that we are the only thread
                 * alerted to check for pending signals, but another thread
                 * should be woken now to take the signal since we will not.
                 * Now we'll wake all the threads in the group just to make
                 * sure someone gets all the pending signals.
                 */
                read_lock(&tasklist_lock);
                spin_lock_irq(&tsk->sighand->siglock);
                for (t = next_thread(tsk); t != tsk; t = next_thread(t))
                        if (!signal_pending(t) && !(t->flags & PF_EXITING)) {
                                recalc_sigpending_tsk(t);
                                if (signal_pending(t))
                                        signal_wake_up(t, 0);
                        }
                spin_unlock_irq(&tsk->sighand->siglock);
                read_unlock(&tasklist_lock);
        }

        write_lock_irq(&tasklist_lock);

        /*
         * 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);
        BUG_ON(!list_empty(&tsk->children));

        /*
         * 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)
         *
         * Case i: Our father is in a different pgrp than we are
         * and we were the only connection outside, so our pgrp
         * is about to become orphaned.
         */
         
        t = tsk->real_parent;
        
        if ((t->pgrp != tsk->pgrp) &&
            (t->session == tsk->session) &&
            will_become_orphaned_pgrp(tsk->pgrp, tsk) &&
            has_stopped_jobs(tsk->pgrp)) {
                __kill_pg_info(SIGHUP, (void *)1, tsk->pgrp);
                __kill_pg_info(SIGCONT, (void *)1, tsk->pgrp);
        }

        /* 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 && tsk->exit_signal != -1 &&
            ( tsk->parent_exec_id != t->self_exec_id  ||
              tsk->self_exec_id != tsk->parent_exec_id)
            && !capable(CAP_KILL))
                tsk->exit_signal = SIGCHLD;


        /* If something other than our normal parent is ptracing us, then
         * send it a SIGCHLD instead of honoring exit_signal.  exit_signal
         * only has special meaning to our real parent.
         */
        if (tsk->exit_signal != -1) {
                int signal = tsk->parent == tsk->real_parent ? tsk->exit_signal : SIGCHLD;
                do_notify_parent(tsk, signal);
        }

        tsk->state = TASK_ZOMBIE;
        /*
         * In the preemption case it must be impossible for the task
         * to get runnable again, so use "_raw_" unlock to keep
         * preempt_count elevated until we schedule().
         *
         * To avoid deadlock on SMP, interrupts must be unmasked.  If we
         * don't, subsequently called functions (e.g, wait_task_inactive()
         * via release_task()) will spin, with interrupt flags
         * unwittingly blocked, until the other task sleeps.  That task
         * may itself be waiting for smp_call_function() to answer and
         * complete, and with interrupts blocked that will never happen.
         */
        _raw_write_unlock(&tasklist_lock);
        local_irq_enable();
}

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

        if (unlikely(in_interrupt()))
                panic("Aiee, killing interrupt handler!");
        if (unlikely(!tsk->pid))
                panic("Attempted to kill the idle task!");
        if (unlikely(tsk->pid == 1))
                panic("Attempted to kill init!");
        tsk->flags |= PF_EXITING;
        del_timer_sync(&tsk->real_timer);

        if (unlikely(in_atomic()))
                printk(KERN_INFO "note: %s[%d] exited with preempt_count %d\n",
                                current->comm, current->pid,
                                preempt_count());

        profile_exit_task(tsk);
 
        if (unlikely(current->ptrace & PT_TRACE_EXIT)) {
                current->ptrace_message = code;
                ptrace_notify((PTRACE_EVENT_EXIT << 8) | SIGTRAP);
        }

        acct_process(code);
        __exit_mm(tsk);

        sem_exit();
        __exit_files(tsk);
        __exit_fs(tsk);
        exit_namespace(tsk);
        exit_itimers(tsk);
        exit_thread();

        if (tsk->leader)
                disassociate_ctty(1);

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

        tsk->exit_code = code;
        exit_notify(tsk);

        if (tsk->exit_signal == -1)
                release_task(tsk);

        schedule();
        BUG();
        /* Avoid "noreturn function does return".  */
        for (;;) ;
}

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

asmlinkage long sys_exit(int error_code)
{
        do_exit((error_code&0xff)<<8);
}

task_t *next_thread(task_t *p)
{
        struct pid_link *link = p->pids + PIDTYPE_TGID;
        struct list_head *tmp, *head = &link->pidptr->task_list;

#ifdef CONFIG_SMP
        if (!p->sighand)
                BUG();
        if (!spin_is_locked(&p->sighand->siglock) &&
                                !rwlock_is_locked(&tasklist_lock))
                BUG();
#endif
        tmp = link->pid_chain.next;
        if (tmp == head)
                tmp = head->next;

        return pid_task(tmp, PIDTYPE_TGID);
}

/*
 * 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)
{
        BUG_ON(exit_code & 0x80); /* core dumps don't get here */

        if (current->signal->group_exit)
                exit_code = current->signal->group_exit_code;
        else if (!thread_group_empty(current)) {
                struct signal_struct *const sig = current->signal;
                struct sighand_struct *const sighand = current->sighand;
                read_lock(&tasklist_lock);
                spin_lock_irq(&sighand->siglock);
                if (sig->group_exit)
                        /* Another thread got here before we took the lock.  */
                        exit_code = sig->group_exit_code;
                else {
                        sig->group_exit = 1;
                        sig->group_exit_code = exit_code;
                        zap_other_threads(current);
                }
                spin_unlock_irq(&sighand->siglock);
                read_unlock(&tasklist_lock);
        }

        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 int eligible_child(pid_t pid, int options, task_t *p)
{
        if (pid > 0) {
                if (p->pid != pid)
                        return 0;
        } else if (!pid) {
                if (p->pgrp != current->pgrp)
                        return 0;
        } else if (pid != -1) {
                if (p->pgrp != -pid)
                        return 0;
        }

        /*
         * Do not consider detached threads that are
         * not ptraced:
         */
        if (p->exit_signal == -1 && !p->ptrace)
                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;
        /*
         * Do not consider thread group leaders that are
         * in a non-empty thread group:
         */
        if (current->tgid != p->tgid && delay_group_leader(p))
                return 2;

        if (security_task_wait(p))
                return 0;

        return 1;
}

/*
 * Handle sys_wait4 work for one task in state TASK_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(task_t *p, unsigned int *stat_addr, struct rusage *ru)
{
        unsigned long state;
        int retval;

        /*
         * Try to move the task's state to DEAD
         * only one thread is allowed to do this:
         */
        state = xchg(&p->state, TASK_DEAD);
        if (state != TASK_ZOMBIE) {
                BUG_ON(state != TASK_DEAD);
                return 0;
        }
        if (unlikely(p->exit_signal == -1))
                /*
                 * This can only happen in a race with a ptraced thread
                 * dying on another processor.
                 */
                return 0;

        /*
         * Now we are sure this task is interesting, and no other
         * thread can reap it because we set its state to TASK_DEAD.
         */
        read_unlock(&tasklist_lock);

        retval = ru ? getrusage(p, RUSAGE_BOTH, ru) : 0;
        if (!retval && stat_addr) {
                if (p->signal->group_exit)
                        retval = put_user(p->signal->group_exit_code, stat_addr);
                else
                        retval = put_user(p->exit_code, stat_addr);
        }
        if (retval) {
                p->state = TASK_ZOMBIE;
                return retval;
        }
        retval = p->pid;
        if (p->real_parent != p->parent) {
                write_lock_irq(&tasklist_lock);
                /* Double-check with lock held.  */
                if (p->real_parent != p->parent) {
                        __ptrace_unlink(p);
                        do_notify_parent(p, p->exit_signal);
                        p->state = TASK_ZOMBIE;
                        p = NULL;
                }
                write_unlock_irq(&tasklist_lock);
        }
        if (p != NULL)
                release_task(p);
        BUG_ON(!retval);
        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(task_t *p, int delayed_group_leader,
                             unsigned int *stat_addr, struct rusage *ru)
{
        int retval, exit_code;

        if (!p->exit_code)
                return 0;
        if (delayed_group_leader && !(p->ptrace & PT_PTRACED) &&
            p->signal && 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.
                 */
                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);
        read_unlock(&tasklist_lock);
        write_lock_irq(&tasklist_lock);

        /*
         * This uses xchg to be atomic with the thread resuming and setting
         * it.  It must also be done with the write lock held to prevent a
         * race with the TASK_ZOMBIE case.
         */
        exit_code = xchg(&p->exit_code, 0);
        if (unlikely(p->state > TASK_STOPPED)) {
                /*
                 * The task resumed and then died.  Let the next iteration
                 * catch it in TASK_ZOMBIE.  Note that exit_code might
                 * already be zero here if it resumed and did _exit(0).
                 * The task itself is dead and won't touch exit_code again;
                 * other processors in this function are locked out.
                 */
                p->exit_code = exit_code;
                exit_code = 0;
        }
        if (unlikely(exit_code == 0)) {
                /*
                 * Another thread in this function got to it first, or it
                 * resumed, or it resumed and then died.
                 */
                write_unlock_irq(&tasklist_lock);
                put_task_struct(p);
                read_lock(&tasklist_lock);
                return 0;
        }

        /* move to end of parent's list to avoid starvation */
        remove_parent(p);
        add_parent(p, p->parent);

        write_unlock_irq(&tasklist_lock);

        retval = ru ? getrusage(p, RUSAGE_BOTH, ru) : 0;
        if (!retval && stat_addr)
                retval = put_user((exit_code << 8) | 0x7f, stat_addr);
        if (!retval)
                retval = p->pid;
        put_task_struct(p);

        BUG_ON(!retval);
        return retval;
}

asmlinkage long sys_wait4(pid_t pid,unsigned int * stat_addr, int options, struct rusage * ru)
{
        DECLARE_WAITQUEUE(wait, current);
        struct task_struct *tsk;
        int flag, retval;

        if (options & ~(WNOHANG|WUNTRACED|__WNOTHREAD|__WCLONE|__WALL))
                return -EINVAL;

        add_wait_queue(&current->wait_chldexit,&wait);
repeat:
        flag = 0;
        current->state = TASK_INTERRUPTIBLE;
        read_lock(&tasklist_lock);
        tsk = current;
        do {
                struct task_struct *p;
                struct list_head *_p;
                int ret;

                list_for_each(_p,&tsk->children) {
                        p = list_entry(_p,struct task_struct,sibling);

                        ret = eligible_child(pid, options, p);
                        if (!ret)
                                continue;
                        flag = 1;

                        switch (p->state) {
                        case TASK_STOPPED:
                                if (!(options & WUNTRACED) &&
                                    !(p->ptrace & PT_PTRACED))
                                        continue;
                                retval = wait_task_stopped(p, ret == 2,
                                                           stat_addr, ru);
                                if (retval != 0) /* He released the lock.  */
                                        goto end_wait4;
                                break;
                        case TASK_ZOMBIE:
                                /*
                                 * Eligible but we cannot release it yet:
                                 */
                                if (ret == 2)
                                        continue;
                                retval = wait_task_zombie(p, stat_addr, ru);
                                if (retval != 0) /* He released the lock.  */
                                        goto end_wait4;
                                break;
                        }
                }
                if (!flag) {
                        list_for_each (_p,&tsk->ptrace_children) {
                                p = list_entry(_p,struct task_struct,ptrace_list);
                                if (!eligible_child(pid, options, p))
                                        continue;
                                flag = 1;
                                break;
                        }
                }
                if (options & __WNOTHREAD)
                        break;
                tsk = next_thread(tsk);
                if (tsk->signal != current->signal)
                        BUG();
        } while (tsk != current);
        read_unlock(&tasklist_lock);
        if (flag) {
                retval = 0;
                if (options & WNOHANG)
                        goto end_wait4;
                retval = -ERESTARTSYS;
                if (signal_pending(current))
                        goto end_wait4;
                schedule();
                goto repeat;
        }
        retval = -ECHILD;
end_wait4:
        current->state = TASK_RUNNING;
        remove_wait_queue(&current->wait_chldexit,&wait);
        return retval;
}

#if !defined(__alpha__) && !defined(__ia64__) && !defined(__arm__)

/*
 * sys_waitpid() remains for compatibility. waitpid() should be
 * implemented by calling sys_wait4() from libc.a.
 */
asmlinkage long sys_waitpid(pid_t pid,unsigned int * stat_addr, int options)
{
        return sys_wait4(pid, stat_addr, options, NULL);
}

#endif