kernel/sched: Fix sched_fork() access an invalid sched_task_group

[linux.git] / kernel / exit.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/kernel/exit.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/sched/autogroup.h>
#include <linux/sched/mm.h>
#include <linux/sched/stat.h>
#include <linux/sched/task.h>
#include <linux/sched/task_stack.h>
#include <linux/sched/cputime.h>
#include <linux/interrupt.h>
#include <linux/module.h>
#include <linux/capability.h>
#include <linux/completion.h>
#include <linux/personality.h>
#include <linux/tty.h>
#include <linux/iocontext.h>
#include <linux/key.h>
#include <linux/cpu.h>
#include <linux/acct.h>
#include <linux/tsacct_kern.h>
#include <linux/file.h>
#include <linux/fdtable.h>
#include <linux/freezer.h>
#include <linux/binfmts.h>
#include <linux/nsproxy.h>
#include <linux/pid_namespace.h>
#include <linux/ptrace.h>
#include <linux/profile.h>
#include <linux/mount.h>
#include <linux/proc_fs.h>
#include <linux/kthread.h>
#include <linux/mempolicy.h>
#include <linux/taskstats_kern.h>
#include <linux/delayacct.h>
#include <linux/cgroup.h>
#include <linux/syscalls.h>
#include <linux/signal.h>
#include <linux/posix-timers.h>
#include <linux/cn_proc.h>
#include <linux/mutex.h>
#include <linux/futex.h>
#include <linux/pipe_fs_i.h>
#include <linux/audit.h> /* for audit_free() */
#include <linux/resource.h>
#include <linux/blkdev.h>
#include <linux/task_io_accounting_ops.h>
#include <linux/tracehook.h>
#include <linux/fs_struct.h>
#include <linux/init_task.h>
#include <linux/perf_event.h>
#include <trace/events/sched.h>
#include <linux/hw_breakpoint.h>
#include <linux/oom.h>
#include <linux/writeback.h>
#include <linux/shm.h>
#include <linux/kcov.h>
#include <linux/random.h>
#include <linux/rcuwait.h>
#include <linux/compat.h>
#include <linux/io_uring.h>
#include <linux/kprobes.h>

#include <linux/uaccess.h>
#include <asm/unistd.h>
#include <asm/mmu_context.h>

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

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

/*
 * This function expects the tasklist_lock write-locked.
 */
static void __exit_signal(struct task_struct *tsk)
{
        struct signal_struct *sig = tsk->signal;
        bool group_dead = thread_group_leader(tsk);
        struct sighand_struct *sighand;
        struct tty_struct *tty;
        u64 utime, stime;

        sighand = rcu_dereference_check(tsk->sighand,
                                        lockdep_tasklist_lock_is_held());
        spin_lock(&sighand->siglock);

#ifdef CONFIG_POSIX_TIMERS
        posix_cpu_timers_exit(tsk);
        if (group_dead)
                posix_cpu_timers_exit_group(tsk);
#endif

        if (group_dead) {
                tty = sig->tty;
                sig->tty = NULL;
        } else {
                /*
                 * If there is any task waiting for the group exit
                 * then notify it:
                 */
                if (sig->notify_count > 0 && !--sig->notify_count)
                        wake_up_process(sig->group_exit_task);

                if (tsk == sig->curr_target)
                        sig->curr_target = next_thread(tsk);
        }

        add_device_randomness((const void*) &tsk->se.sum_exec_runtime,
                              sizeof(unsigned long long));

        /*
         * Accumulate here the counters for all threads as they die. We could
         * skip the group leader because it is the last user of signal_struct,
         * but we want to avoid the race with thread_group_cputime() which can
         * see the empty ->thread_head list.
         */
        task_cputime(tsk, &utime, &stime);
        write_seqlock(&sig->stats_lock);
        sig->utime += utime;
        sig->stime += stime;
        sig->gtime += task_gtime(tsk);
        sig->min_flt += tsk->min_flt;
        sig->maj_flt += tsk->maj_flt;
        sig->nvcsw += tsk->nvcsw;
        sig->nivcsw += tsk->nivcsw;
        sig->inblock += task_io_get_inblock(tsk);
        sig->oublock += task_io_get_oublock(tsk);
        task_io_accounting_add(&sig->ioac, &tsk->ioac);
        sig->sum_sched_runtime += tsk->se.sum_exec_runtime;
        sig->nr_threads--;
        __unhash_process(tsk, group_dead);
        write_sequnlock(&sig->stats_lock);

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

        __cleanup_sighand(sighand);
        clear_tsk_thread_flag(tsk, TIF_SIGPENDING);
        if (group_dead) {
                flush_sigqueue(&sig->shared_pending);
                tty_kref_put(tty);
        }
}

static void delayed_put_task_struct(struct rcu_head *rhp)
{
        struct task_struct *tsk = container_of(rhp, struct task_struct, rcu);

        kprobe_flush_task(tsk);
        perf_event_delayed_put(tsk);
        trace_sched_process_free(tsk);
        put_task_struct(tsk);
}

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

void release_task(struct task_struct *p)
{
        struct task_struct *leader;
        struct pid *thread_pid;
        int zap_leader;
repeat:
        /* don't need to get the RCU readlock here - the process is dead and
         * can't be modifying its own credentials. But shut RCU-lockdep up */
        rcu_read_lock();
        dec_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
        rcu_read_unlock();

        cgroup_release(p);

        write_lock_irq(&tasklist_lock);
        ptrace_release_task(p);
        thread_pid = get_pid(p->thread_pid);
        __exit_signal(p);

        /*
         * If we are the last non-leader member of the thread
         * group, and the leader is zombie, then notify the
         * group leader's parent process. (if it wants notification.)
         */
        zap_leader = 0;
        leader = p->group_leader;
        if (leader != p && thread_group_empty(leader)
                        && leader->exit_state == EXIT_ZOMBIE) {
                /*
                 * If we were the last child thread and the leader has
                 * exited already, and the leader's parent ignores SIGCHLD,
                 * then we are the one who should release the leader.
                 */
                zap_leader = do_notify_parent(leader, leader->exit_signal);
                if (zap_leader)
                        leader->exit_state = EXIT_DEAD;
        }

        write_unlock_irq(&tasklist_lock);
        seccomp_filter_release(p);
        proc_flush_pid(thread_pid);
        put_pid(thread_pid);
        release_thread(p);
        put_task_struct_rcu_user(p);

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

int rcuwait_wake_up(struct rcuwait *w)
{
        int ret = 0;
        struct task_struct *task;

        rcu_read_lock();

        /*
         * Order condition vs @task, such that everything prior to the load
         * of @task is visible. This is the condition as to why the user called
         * rcuwait_wake() in the first place. Pairs with set_current_state()
         * barrier (A) in rcuwait_wait_event().
         *
         *    WAIT                WAKE
         *    [S] tsk = current   [S] cond = true
         *        MB (A)              MB (B)
         *    [L] cond            [L] tsk
         */
        smp_mb(); /* (B) */

        task = rcu_dereference(w->task);
        if (task)
                ret = wake_up_process(task);
        rcu_read_unlock();

        return ret;
}
EXPORT_SYMBOL_GPL(rcuwait_wake_up);

/*
 * Determine if a process group is "orphaned", according to the POSIX
 * definition in 2.2.2.52.  Orphaned process groups are not to be affected
 * by terminal-generated stop signals.  Newly orphaned process groups are
 * to receive a SIGHUP and a SIGCONT.
 *
 * "I ask you, have you ever known what it is to be an orphan?"
 */
static int will_become_orphaned_pgrp(struct pid *pgrp,
                                        struct task_struct *ignored_task)
{
        struct task_struct *p;

        do_each_pid_task(pgrp, PIDTYPE_PGID, p) {
                if ((p == ignored_task) ||
                    (p->exit_state && thread_group_empty(p)) ||
                    is_global_init(p->real_parent))
                        continue;

                if (task_pgrp(p->real_parent) != pgrp &&
                    task_session(p->real_parent) == task_session(p))
                        return 0;
        } while_each_pid_task(pgrp, PIDTYPE_PGID, p);

        return 1;
}

int is_current_pgrp_orphaned(void)
{
        int retval;

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

        return retval;
}

static bool has_stopped_jobs(struct pid *pgrp)
{
        struct task_struct *p;

        do_each_pid_task(pgrp, PIDTYPE_PGID, p) {
                if (p->signal->flags & SIGNAL_STOP_STOPPED)
                        return true;
        } while_each_pid_task(pgrp, PIDTYPE_PGID, p);

        return false;
}

/*
 * Check to see if any process groups have become orphaned as
 * a result of our exiting, and if they have any stopped jobs,
 * send them a SIGHUP and then a SIGCONT. (POSIX 3.2.2.2)
 */
static void
kill_orphaned_pgrp(struct task_struct *tsk, struct task_struct *parent)
{
        struct pid *pgrp = task_pgrp(tsk);
        struct task_struct *ignored_task = tsk;

        if (!parent)
                /* exit: our father is in a different pgrp than
                 * we are and we were the only connection outside.
                 */
                parent = tsk->real_parent;
        else
                /* reparent: our child is in a different pgrp than
                 * we are, and it was the only connection outside.
                 */
                ignored_task = NULL;

        if (task_pgrp(parent) != pgrp &&
            task_session(parent) == task_session(tsk) &&
            will_become_orphaned_pgrp(pgrp, ignored_task) &&
            has_stopped_jobs(pgrp)) {
                __kill_pgrp_info(SIGHUP, SEND_SIG_PRIV, pgrp);
                __kill_pgrp_info(SIGCONT, SEND_SIG_PRIV, pgrp);
        }
}

#ifdef CONFIG_MEMCG
/*
 * A task is exiting.   If it owned this mm, find a new owner for the mm.
 */
void mm_update_next_owner(struct mm_struct *mm)
{
        struct task_struct *c, *g, *p = current;

retry:
        /*
         * If the exiting or execing task is not the owner, it's
         * someone else's problem.
         */
        if (mm->owner != p)
                return;
        /*
         * The current owner is exiting/execing and there are no other
         * candidates.  Do not leave the mm pointing to a possibly
         * freed task structure.
         */
        if (atomic_read(&mm->mm_users) <= 1) {
                WRITE_ONCE(mm->owner, NULL);
                return;
        }

        read_lock(&tasklist_lock);
        /*
         * Search in the children
         */
        list_for_each_entry(c, &p->children, sibling) {
                if (c->mm == mm)
                        goto assign_new_owner;
        }

        /*
         * Search in the siblings
         */
        list_for_each_entry(c, &p->real_parent->children, sibling) {
                if (c->mm == mm)
                        goto assign_new_owner;
        }

        /*
         * Search through everything else, we should not get here often.
         */
        for_each_process(g) {
                if (g->flags & PF_KTHREAD)
                        continue;
                for_each_thread(g, c) {
                        if (c->mm == mm)
                                goto assign_new_owner;
                        if (c->mm)
                                break;
                }
        }
        read_unlock(&tasklist_lock);
        /*
         * We found no owner yet mm_users > 1: this implies that we are
         * most likely racing with swapoff (try_to_unuse()) or /proc or
         * ptrace or page migration (get_task_mm()).  Mark owner as NULL.
         */
        WRITE_ONCE(mm->owner, NULL);
        return;

assign_new_owner:
        BUG_ON(c == p);
        get_task_struct(c);
        /*
         * The task_lock protects c->mm from changing.
         * We always want mm->owner->mm == mm
         */
        task_lock(c);
        /*
         * Delay read_unlock() till we have the task_lock()
         * to ensure that c does not slip away underneath us
         */
        read_unlock(&tasklist_lock);
        if (c->mm != mm) {
                task_unlock(c);
                put_task_struct(c);
                goto retry;
        }
        WRITE_ONCE(mm->owner, c);
        task_unlock(c);
        put_task_struct(c);
}
#endif /* CONFIG_MEMCG */

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

        exit_mm_release(current, mm);
        if (!mm)
                return;
        sync_mm_rss(mm);
        /*
         * Serialize with any possible pending coredump.
         * We must hold mmap_lock around checking core_state
         * and clearing tsk->mm.  The core-inducing thread
         * will increment ->nr_threads for each thread in the
         * group with ->mm != NULL.
         */
        mmap_read_lock(mm);
        core_state = mm->core_state;
        if (core_state) {
                struct core_thread self;

                mmap_read_unlock(mm);

                self.task = current;
                if (self.task->flags & PF_SIGNALED)
                        self.next = xchg(&core_state->dumper.next, &self);
                else
                        self.task = NULL;
                /*
                 * Implies mb(), the result of xchg() must be visible
                 * to core_state->dumper.
                 */
                if (atomic_dec_and_test(&core_state->nr_threads))
                        complete(&core_state->startup);

                for (;;) {
                        set_current_state(TASK_UNINTERRUPTIBLE);
                        if (!self.task) /* see coredump_finish() */
                                break;
                        freezable_schedule();
                }
                __set_current_state(TASK_RUNNING);
                mmap_read_lock(mm);
        }
        mmgrab(mm);
        BUG_ON(mm != current->active_mm);
        /* more a memory barrier than a real lock */
        task_lock(current);
        /*
         * When a thread stops operating on an address space, the loop
         * in membarrier_private_expedited() may not observe that
         * tsk->mm, and the loop in membarrier_global_expedited() may
         * not observe a MEMBARRIER_STATE_GLOBAL_EXPEDITED
         * rq->membarrier_state, so those would not issue an IPI.
         * Membarrier requires a memory barrier after accessing
         * user-space memory, before clearing tsk->mm or the
         * rq->membarrier_state.
         */
        smp_mb__after_spinlock();
        local_irq_disable();
        current->mm = NULL;
        membarrier_update_current_mm(NULL);
        enter_lazy_tlb(mm, current);
        local_irq_enable();
        task_unlock(current);
        mmap_read_unlock(mm);
        mm_update_next_owner(mm);
        mmput(mm);
        if (test_thread_flag(TIF_MEMDIE))
                exit_oom_victim();
}

static struct task_struct *find_alive_thread(struct task_struct *p)
{
        struct task_struct *t;

        for_each_thread(p, t) {
                if (!(t->flags & PF_EXITING))
                        return t;
        }
        return NULL;
}

static struct task_struct *find_child_reaper(struct task_struct *father,
                                                struct list_head *dead)
        __releases(&tasklist_lock)
        __acquires(&tasklist_lock)
{
        struct pid_namespace *pid_ns = task_active_pid_ns(father);
        struct task_struct *reaper = pid_ns->child_reaper;
        struct task_struct *p, *n;

        if (likely(reaper != father))
                return reaper;

        reaper = find_alive_thread(father);
        if (reaper) {
                pid_ns->child_reaper = reaper;
                return reaper;
        }

        write_unlock_irq(&tasklist_lock);

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

        zap_pid_ns_processes(pid_ns);
        write_lock_irq(&tasklist_lock);

        return father;
}

/*
 * When we die, we re-parent all our children, and try to:
 * 1. give them to another thread in our thread group, if such a member exists
 * 2. give it to the first ancestor process which prctl'd itself as a
 *    child_subreaper for its children (like a service manager)
 * 3. give it to the init process (PID 1) in our pid namespace
 */
static struct task_struct *find_new_reaper(struct task_struct *father,
                                           struct task_struct *child_reaper)
{
        struct task_struct *thread, *reaper;

        thread = find_alive_thread(father);
        if (thread)
                return thread;

        if (father->signal->has_child_subreaper) {
                unsigned int ns_level = task_pid(father)->level;
                /*
                 * Find the first ->is_child_subreaper ancestor in our pid_ns.
                 * We can't check reaper != child_reaper to ensure we do not
                 * cross the namespaces, the exiting parent could be injected
                 * by setns() + fork().
                 * We check pid->level, this is slightly more efficient than
                 * task_active_pid_ns(reaper) != task_active_pid_ns(father).
                 */
                for (reaper = father->real_parent;
                     task_pid(reaper)->level == ns_level;
                     reaper = reaper->real_parent) {
                        if (reaper == &init_task)
                                break;
                        if (!reaper->signal->is_child_subreaper)
                                continue;
                        thread = find_alive_thread(reaper);
                        if (thread)
                                return thread;
                }
        }

        return child_reaper;
}

/*
* Any that need to be release_task'd are put on the @dead list.
 */
static void reparent_leader(struct task_struct *father, struct task_struct *p,
                                struct list_head *dead)
{
        if (unlikely(p->exit_state == EXIT_DEAD))
                return;

        /* We don't want people slaying init. */
        p->exit_signal = SIGCHLD;

        /* If it has exited notify the new parent about this child's death. */
        if (!p->ptrace &&
            p->exit_state == EXIT_ZOMBIE && thread_group_empty(p)) {
                if (do_notify_parent(p, p->exit_signal)) {
                        p->exit_state = EXIT_DEAD;
                        list_add(&p->ptrace_entry, dead);
                }
        }

        kill_orphaned_pgrp(p, father);
}

/*
 * This does two things:
 *
 * A.  Make init inherit all the child processes
 * B.  Check to see if any process groups have become orphaned
 *      as a result of our exiting, and if they have any stopped
 *      jobs, send them a SIGHUP and then a SIGCONT.  (POSIX 3.2.2.2)
 */
static void forget_original_parent(struct task_struct *father,
                                        struct list_head *dead)
{
        struct task_struct *p, *t, *reaper;

        if (unlikely(!list_empty(&father->ptraced)))
                exit_ptrace(father, dead);

        /* Can drop and reacquire tasklist_lock */
        reaper = find_child_reaper(father, dead);
        if (list_empty(&father->children))
                return;

        reaper = find_new_reaper(father, reaper);
        list_for_each_entry(p, &father->children, sibling) {
                for_each_thread(p, t) {
                        RCU_INIT_POINTER(t->real_parent, reaper);
                        BUG_ON((!t->ptrace) != (rcu_access_pointer(t->parent) == father));
                        if (likely(!t->ptrace))
                                t->parent = t->real_parent;
                        if (t->pdeath_signal)
                                group_send_sig_info(t->pdeath_signal,
                                                    SEND_SIG_NOINFO, t,
                                                    PIDTYPE_TGID);
                }
                /*
                 * If this is a threaded reparent there is no need to
                 * notify anyone anything has happened.
                 */
                if (!same_thread_group(reaper, father))
                        reparent_leader(father, p, dead);
        }
        list_splice_tail_init(&father->children, &reaper->children);
}

/*
 * Send signals to all our closest relatives so that they know
 * to properly mourn us..
 */
static void exit_notify(struct task_struct *tsk, int group_dead)
{
        bool autoreap;
        struct task_struct *p, *n;
        LIST_HEAD(dead);

        write_lock_irq(&tasklist_lock);
        forget_original_parent(tsk, &dead);

        if (group_dead)
                kill_orphaned_pgrp(tsk->group_leader, NULL);

        tsk->exit_state = EXIT_ZOMBIE;
        if (unlikely(tsk->ptrace)) {
                int sig = thread_group_leader(tsk) &&
                                thread_group_empty(tsk) &&
                                !ptrace_reparented(tsk) ?
                        tsk->exit_signal : SIGCHLD;
                autoreap = do_notify_parent(tsk, sig);
        } else if (thread_group_leader(tsk)) {
                autoreap = thread_group_empty(tsk) &&
                        do_notify_parent(tsk, tsk->exit_signal);
        } else {
                autoreap = true;
        }

        if (autoreap) {
                tsk->exit_state = EXIT_DEAD;
                list_add(&tsk->ptrace_entry, &dead);
        }

        /* mt-exec, de_thread() is waiting for group leader */
        if (unlikely(tsk->signal->notify_count < 0))
                wake_up_process(tsk->signal->group_exit_task);
        write_unlock_irq(&tasklist_lock);

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

#ifdef CONFIG_DEBUG_STACK_USAGE
static void check_stack_usage(void)
{
        static DEFINE_SPINLOCK(low_water_lock);
        static int lowest_to_date = THREAD_SIZE;
        unsigned long free;

        free = stack_not_used(current);

        if (free >= lowest_to_date)
                return;

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

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

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

        WARN_ON(blk_needs_flush_plug(tsk));

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

        /*
         * If do_exit is called because this processes oopsed, it's possible
         * that get_fs() was left as KERNEL_DS, so reset it to USER_DS before
         * continuing. Amongst other possible reasons, this is to prevent
         * mm_release()->clear_child_tid() from writing to a user-controlled
         * kernel address.
         */
        force_uaccess_begin();

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

        profile_task_exit(tsk);
        kcov_task_exit(tsk);

        ptrace_event(PTRACE_EVENT_EXIT, code);

        validate_creds_for_do_exit(tsk);

        /*
         * We're taking recursive faults here in do_exit. Safest is to just
         * leave this task alone and wait for reboot.
         */
        if (unlikely(tsk->flags & PF_EXITING)) {
                pr_alert("Fixing recursive fault but reboot is needed!\n");
                futex_exit_recursive(tsk);
                set_current_state(TASK_UNINTERRUPTIBLE);
                schedule();
        }

        io_uring_files_cancel();
        exit_signals(tsk);  /* sets PF_EXITING */

        /* sync mm's RSS info before statistics gathering */
        if (tsk->mm)
                sync_mm_rss(tsk->mm);
        acct_update_integrals(tsk);
        group_dead = atomic_dec_and_test(&tsk->signal->live);
        if (group_dead) {
                /*
                 * If the last thread of global init has exited, panic
                 * immediately to get a useable coredump.
                 */
                if (unlikely(is_global_init(tsk)))
                        panic("Attempted to kill init! exitcode=0x%08x\n",
                                tsk->signal->group_exit_code ?: (int)code);

#ifdef CONFIG_POSIX_TIMERS
                hrtimer_cancel(&tsk->signal->real_timer);
                exit_itimers(tsk->signal);
#endif
                if (tsk->mm)
                        setmax_mm_hiwater_rss(&tsk->signal->maxrss, tsk->mm);
        }
        acct_collect(code, group_dead);
        if (group_dead)
                tty_audit_exit();
        audit_free(tsk);

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

        exit_mm();

        if (group_dead)
                acct_process();
        trace_sched_process_exit(tsk);

        exit_sem(tsk);
        exit_shm(tsk);
        exit_files(tsk);
        exit_fs(tsk);
        if (group_dead)
                disassociate_ctty(1);
        exit_task_namespaces(tsk);
        exit_task_work(tsk);
        exit_thread(tsk);

        /*
         * Flush inherited counters to the parent - before the parent
         * gets woken up by child-exit notifications.
         *
         * because of cgroup mode, must be called before cgroup_exit()
         */
        perf_event_exit_task(tsk);

        sched_autogroup_exit_task(tsk);
        cgroup_exit(tsk);

        /*
         * FIXME: do that only when needed, using sched_exit tracepoint
         */
        flush_ptrace_hw_breakpoint(tsk);

        exit_tasks_rcu_start();
        exit_notify(tsk, group_dead);
        proc_exit_connector(tsk);
        mpol_put_task_policy(tsk);
#ifdef CONFIG_FUTEX
        if (unlikely(current->pi_state_cache))
                kfree(current->pi_state_cache);
#endif
        /*
         * Make sure we are holding no locks:
         */
        debug_check_no_locks_held();

        if (tsk->io_context)
                exit_io_context(tsk);

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

        if (tsk->task_frag.page)
                put_page(tsk->task_frag.page);

        validate_creds_for_do_exit(tsk);

        check_stack_usage();
        preempt_disable();
        if (tsk->nr_dirtied)
                __this_cpu_add(dirty_throttle_leaks, tsk->nr_dirtied);
        exit_rcu();
        exit_tasks_rcu_finish();

        lockdep_free_task(tsk);
        do_task_dead();
}
EXPORT_SYMBOL_GPL(do_exit);

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

        do_exit(code);
}
EXPORT_SYMBOL(complete_and_exit);

SYSCALL_DEFINE1(exit, int, error_code)
{
        do_exit((error_code&0xff)<<8);
}

/*
 * Take down every thread in the group.  This is called by fatal signals
 * as well as by sys_exit_group (below).
 */
void
do_group_exit(int exit_code)
{
        struct signal_struct *sig = current->signal;

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

        if (signal_group_exit(sig))
                exit_code = sig->group_exit_code;
        else if (!thread_group_empty(current)) {
                struct sighand_struct *const sighand = current->sighand;

                spin_lock_irq(&sighand->siglock);
                if (signal_group_exit(sig))
                        /* Another thread got here before we took the lock.  */
                        exit_code = sig->group_exit_code;
                else {
                        sig->group_exit_code = exit_code;
                        sig->flags = SIGNAL_GROUP_EXIT;
                        zap_other_threads(current);
                }
                spin_unlock_irq(&sighand->siglock);
        }

        do_exit(exit_code);
        /* NOTREACHED */
}

/*
 * this kills every thread in the thread group. Note that any externally
 * wait4()-ing process will get the correct exit code - even if this
 * thread is not the thread group leader.
 */
SYSCALL_DEFINE1(exit_group, int, error_code)
{
        do_group_exit((error_code & 0xff) << 8);
        /* NOTREACHED */
        return 0;
}

struct waitid_info {
        pid_t pid;
        uid_t uid;
        int status;
        int cause;
};

struct wait_opts {
        enum pid_type           wo_type;
        int                     wo_flags;
        struct pid              *wo_pid;

        struct waitid_info      *wo_info;
        int                     wo_stat;
        struct rusage           *wo_rusage;

        wait_queue_entry_t              child_wait;
        int                     notask_error;
};

static int eligible_pid(struct wait_opts *wo, struct task_struct *p)
{
        return  wo->wo_type == PIDTYPE_MAX ||
                task_pid_type(p, wo->wo_type) == wo->wo_pid;
}

static int
eligible_child(struct wait_opts *wo, bool ptrace, struct task_struct *p)
{
        if (!eligible_pid(wo, p))
                return 0;

        /*
         * Wait for all children (clone and not) if __WALL is set or
         * if it is traced by us.
         */
        if (ptrace || (wo->wo_flags & __WALL))
                return 1;

        /*
         * Otherwise, wait for clone children *only* if __WCLONE is set;
         * otherwise, wait for non-clone children *only*.
         *
         * Note: a "clone" child here is one that reports to its parent
         * using a signal other than SIGCHLD, or a non-leader thread which
         * we can only see if it is traced by us.
         */
        if ((p->exit_signal != SIGCHLD) ^ !!(wo->wo_flags & __WCLONE))
                return 0;

        return 1;
}

/*
 * Handle sys_wait4 work for one task in state EXIT_ZOMBIE.  We hold
 * read_lock(&tasklist_lock) on entry.  If we return zero, we still hold
 * the lock and this task is uninteresting.  If we return nonzero, we have
 * released the lock and the system call should return.
 */
static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)
{
        int state, status;
        pid_t pid = task_pid_vnr(p);
        uid_t uid = from_kuid_munged(current_user_ns(), task_uid(p));
        struct waitid_info *infop;

        if (!likely(wo->wo_flags & WEXITED))
                return 0;

        if (unlikely(wo->wo_flags & WNOWAIT)) {
                status = p->exit_code;
                get_task_struct(p);
                read_unlock(&tasklist_lock);
                sched_annotate_sleep();
                if (wo->wo_rusage)
                        getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
                put_task_struct(p);
                goto out_info;
        }
        /*
         * Move the task's state to DEAD/TRACE, only one thread can do this.
         */
        state = (ptrace_reparented(p) && thread_group_leader(p)) ?
                EXIT_TRACE : EXIT_DEAD;
        if (cmpxchg(&p->exit_state, EXIT_ZOMBIE, state) != EXIT_ZOMBIE)
                return 0;
        /*
         * We own this thread, nobody else can reap it.
         */
        read_unlock(&tasklist_lock);
        sched_annotate_sleep();

        /*
         * Check thread_group_leader() to exclude the traced sub-threads.
         */
        if (state == EXIT_DEAD && thread_group_leader(p)) {
                struct signal_struct *sig = p->signal;
                struct signal_struct *psig = current->signal;
                unsigned long maxrss;
                u64 tgutime, tgstime;

                /*
                 * The resource counters for the group leader are in its
                 * own task_struct.  Those for dead threads in the group
                 * are in its signal_struct, as are those for the child
                 * processes it has previously reaped.  All these
                 * accumulate in the parent's signal_struct c* fields.
                 *
                 * We don't bother to take a lock here to protect these
                 * p->signal fields because the whole thread group is dead
                 * and nobody can change them.
                 *
                 * psig->stats_lock also protects us from our sub-theads
                 * which can reap other children at the same time. Until
                 * we change k_getrusage()-like users to rely on this lock
                 * we have to take ->siglock as well.
                 *
                 * We use thread_group_cputime_adjusted() to get times for
                 * the thread group, which consolidates times for all threads
                 * in the group including the group leader.
                 */
                thread_group_cputime_adjusted(p, &tgutime, &tgstime);
                spin_lock_irq(&current->sighand->siglock);
                write_seqlock(&psig->stats_lock);
                psig->cutime += tgutime + sig->cutime;
                psig->cstime += tgstime + sig->cstime;
                psig->cgtime += task_gtime(p) + sig->gtime + sig->cgtime;
                psig->cmin_flt +=
                        p->min_flt + sig->min_flt + sig->cmin_flt;
                psig->cmaj_flt +=
                        p->maj_flt + sig->maj_flt + sig->cmaj_flt;
                psig->cnvcsw +=
                        p->nvcsw + sig->nvcsw + sig->cnvcsw;
                psig->cnivcsw +=
                        p->nivcsw + sig->nivcsw + sig->cnivcsw;
                psig->cinblock +=
                        task_io_get_inblock(p) +
                        sig->inblock + sig->cinblock;
                psig->coublock +=
                        task_io_get_oublock(p) +
                        sig->oublock + sig->coublock;
                maxrss = max(sig->maxrss, sig->cmaxrss);
                if (psig->cmaxrss < maxrss)
                        psig->cmaxrss = maxrss;
                task_io_accounting_add(&psig->ioac, &p->ioac);
                task_io_accounting_add(&psig->ioac, &sig->ioac);
                write_sequnlock(&psig->stats_lock);
                spin_unlock_irq(&current->sighand->siglock);
        }

        if (wo->wo_rusage)
                getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
        status = (p->signal->flags & SIGNAL_GROUP_EXIT)
                ? p->signal->group_exit_code : p->exit_code;
        wo->wo_stat = status;

        if (state == EXIT_TRACE) {
                write_lock_irq(&tasklist_lock);
                /* We dropped tasklist, ptracer could die and untrace */
                ptrace_unlink(p);

                /* If parent wants a zombie, don't release it now */
                state = EXIT_ZOMBIE;
                if (do_notify_parent(p, p->exit_signal))
                        state = EXIT_DEAD;
                p->exit_state = state;
                write_unlock_irq(&tasklist_lock);
        }
        if (state == EXIT_DEAD)
                release_task(p);

out_info:
        infop = wo->wo_info;
        if (infop) {
                if ((status & 0x7f) == 0) {
                        infop->cause = CLD_EXITED;
                        infop->status = status >> 8;
                } else {
                        infop->cause = (status & 0x80) ? CLD_DUMPED : CLD_KILLED;
                        infop->status = status & 0x7f;
                }
                infop->pid = pid;
                infop->uid = uid;
        }

        return pid;
}

static int *task_stopped_code(struct task_struct *p, bool ptrace)
{
        if (ptrace) {
                if (task_is_traced(p) && !(p->jobctl & JOBCTL_LISTENING))
                        return &p->exit_code;
        } else {
                if (p->signal->flags & SIGNAL_STOP_STOPPED)
                        return &p->signal->group_exit_code;
        }
        return NULL;
}

/**
 * wait_task_stopped - Wait for %TASK_STOPPED or %TASK_TRACED
 * @wo: wait options
 * @ptrace: is the wait for ptrace
 * @p: task to wait for
 *
 * Handle sys_wait4() work for %p in state %TASK_STOPPED or %TASK_TRACED.
 *
 * CONTEXT:
 * read_lock(&tasklist_lock), which is released if return value is
 * non-zero.  Also, grabs and releases @p->sighand->siglock.
 *
 * RETURNS:
 * 0 if wait condition didn't exist and search for other wait conditions
 * should continue.  Non-zero return, -errno on failure and @p's pid on
 * success, implies that tasklist_lock is released and wait condition
 * search should terminate.
 */
static int wait_task_stopped(struct wait_opts *wo,
                                int ptrace, struct task_struct *p)
{
        struct waitid_info *infop;
        int exit_code, *p_code, why;
        uid_t uid = 0; /* unneeded, required by compiler */
        pid_t pid;

        /*
         * Traditionally we see ptrace'd stopped tasks regardless of options.
         */
        if (!ptrace && !(wo->wo_flags & WUNTRACED))
                return 0;

        if (!task_stopped_code(p, ptrace))
                return 0;

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

        p_code = task_stopped_code(p, ptrace);
        if (unlikely(!p_code))
                goto unlock_sig;

        exit_code = *p_code;
        if (!exit_code)
                goto unlock_sig;

        if (!unlikely(wo->wo_flags & WNOWAIT))
                *p_code = 0;

        uid = from_kuid_munged(current_user_ns(), task_uid(p));
unlock_sig:
        spin_unlock_irq(&p->sighand->siglock);
        if (!exit_code)
                return 0;

        /*
         * Now we are pretty sure this task is interesting.
         * Make sure it doesn't get reaped out from under us while we
         * give up the lock and then examine it below.  We don't want to
         * keep holding onto the tasklist_lock while we call getrusage and
         * possibly take page faults for user memory.
         */
        get_task_struct(p);
        pid = task_pid_vnr(p);
        why = ptrace ? CLD_TRAPPED : CLD_STOPPED;
        read_unlock(&tasklist_lock);
        sched_annotate_sleep();
        if (wo->wo_rusage)
                getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
        put_task_struct(p);

        if (likely(!(wo->wo_flags & WNOWAIT)))
                wo->wo_stat = (exit_code << 8) | 0x7f;

        infop = wo->wo_info;
        if (infop) {
                infop->cause = why;
                infop->status = exit_code;
                infop->pid = pid;
                infop->uid = uid;
        }
        return pid;
}

/*
 * Handle do_wait work for one task in a live, non-stopped state.
 * read_lock(&tasklist_lock) on entry.  If we return zero, we still hold
 * the lock and this task is uninteresting.  If we return nonzero, we have
 * released the lock and the system call should return.
 */
static int wait_task_continued(struct wait_opts *wo, struct task_struct *p)
{
        struct waitid_info *infop;
        pid_t pid;
        uid_t uid;

        if (!unlikely(wo->wo_flags & WCONTINUED))
                return 0;

        if (!(p->signal->flags & SIGNAL_STOP_CONTINUED))
                return 0;

        spin_lock_irq(&p->sighand->siglock);
        /* Re-check with the lock held.  */
        if (!(p->signal->flags & SIGNAL_STOP_CONTINUED)) {
                spin_unlock_irq(&p->sighand->siglock);
                return 0;
        }
        if (!unlikely(wo->wo_flags & WNOWAIT))
                p->signal->flags &= ~SIGNAL_STOP_CONTINUED;
        uid = from_kuid_munged(current_user_ns(), task_uid(p));
        spin_unlock_irq(&p->sighand->siglock);

        pid = task_pid_vnr(p);
        get_task_struct(p);
        read_unlock(&tasklist_lock);
        sched_annotate_sleep();
        if (wo->wo_rusage)
                getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
        put_task_struct(p);

        infop = wo->wo_info;
        if (!infop) {
                wo->wo_stat = 0xffff;
        } else {
                infop->cause = CLD_CONTINUED;
                infop->pid = pid;
                infop->uid = uid;
                infop->status = SIGCONT;
        }
        return pid;
}

/*
 * Consider @p for a wait by @parent.
 *
 * -ECHILD should be in ->notask_error before the first call.
 * Returns nonzero for a final return, when we have unlocked tasklist_lock.
 * Returns zero if the search for a child should continue;
 * then ->notask_error is 0 if @p is an eligible child,
 * or still -ECHILD.
 */
static int wait_consider_task(struct wait_opts *wo, int ptrace,
                                struct task_struct *p)
{
        /*
         * We can race with wait_task_zombie() from another thread.
         * Ensure that EXIT_ZOMBIE -> EXIT_DEAD/EXIT_TRACE transition
         * can't confuse the checks below.
         */
        int exit_state = READ_ONCE(p->exit_state);
        int ret;

        if (unlikely(exit_state == EXIT_DEAD))
                return 0;

        ret = eligible_child(wo, ptrace, p);
        if (!ret)
                return ret;

        if (unlikely(exit_state == EXIT_TRACE)) {
                /*
                 * ptrace == 0 means we are the natural parent. In this case
                 * we should clear notask_error, debugger will notify us.
                 */
                if (likely(!ptrace))
                        wo->notask_error = 0;
                return 0;
        }

        if (likely(!ptrace) && unlikely(p->ptrace)) {
                /*
                 * If it is traced by its real parent's group, just pretend
                 * the caller is ptrace_do_wait() and reap this child if it
                 * is zombie.
                 *
                 * This also hides group stop state from real parent; otherwise
                 * a single stop can be reported twice as group and ptrace stop.
                 * If a ptracer wants to distinguish these two events for its
                 * own children it should create a separate process which takes
                 * the role of real parent.
                 */
                if (!ptrace_reparented(p))
                        ptrace = 1;
        }

        /* slay zombie? */
        if (exit_state == EXIT_ZOMBIE) {
                /* we don't reap group leaders with subthreads */
                if (!delay_group_leader(p)) {
                        /*
                         * A zombie ptracee is only visible to its ptracer.
                         * Notification and reaping will be cascaded to the
                         * real parent when the ptracer detaches.
                         */
                        if (unlikely(ptrace) || likely(!p->ptrace))
                                return wait_task_zombie(wo, p);
                }

                /*
                 * Allow access to stopped/continued state via zombie by
                 * falling through.  Clearing of notask_error is complex.
                 *
                 * When !@ptrace:
                 *
                 * If WEXITED is set, notask_error should naturally be
                 * cleared.  If not, subset of WSTOPPED|WCONTINUED is set,
                 * so, if there are live subthreads, there are events to
                 * wait for.  If all subthreads are dead, it's still safe
                 * to clear - this function will be called again in finite
                 * amount time once all the subthreads are released and
                 * will then return without clearing.
                 *
                 * When @ptrace:
                 *
                 * Stopped state is per-task and thus can't change once the
                 * target task dies.  Only continued and exited can happen.
                 * Clear notask_error if WCONTINUED | WEXITED.
                 */
                if (likely(!ptrace) || (wo->wo_flags & (WCONTINUED | WEXITED)))
                        wo->notask_error = 0;
        } else {
                /*
                 * @p is alive and it's gonna stop, continue or exit, so
                 * there always is something to wait for.
                 */
                wo->notask_error = 0;
        }

        /*
         * Wait for stopped.  Depending on @ptrace, different stopped state
         * is used and the two don't interact with each other.
         */
        ret = wait_task_stopped(wo, ptrace, p);
        if (ret)
                return ret;

        /*
         * Wait for continued.  There's only one continued state and the
         * ptracer can consume it which can confuse the real parent.  Don't
         * use WCONTINUED from ptracer.  You don't need or want it.
         */
        return wait_task_continued(wo, p);
}

/*
 * Do the work of do_wait() for one thread in the group, @tsk.
 *
 * -ECHILD should be in ->notask_error before the first call.
 * Returns nonzero for a final return, when we have unlocked tasklist_lock.
 * Returns zero if the search for a child should continue; then
 * ->notask_error is 0 if there were any eligible children,
 * or still -ECHILD.
 */
static int do_wait_thread(struct wait_opts *wo, struct task_struct *tsk)
{
        struct task_struct *p;

        list_for_each_entry(p, &tsk->children, sibling) {
                int ret = wait_consider_task(wo, 0, p);

                if (ret)
                        return ret;
        }

        return 0;
}

static int ptrace_do_wait(struct wait_opts *wo, struct task_struct *tsk)
{
        struct task_struct *p;

        list_for_each_entry(p, &tsk->ptraced, ptrace_entry) {
                int ret = wait_consider_task(wo, 1, p);

                if (ret)
                        return ret;
        }

        return 0;
}

static int child_wait_callback(wait_queue_entry_t *wait, unsigned mode,
                                int sync, void *key)
{
        struct wait_opts *wo = container_of(wait, struct wait_opts,
                                                child_wait);
        struct task_struct *p = key;

        if (!eligible_pid(wo, p))
                return 0;

        if ((wo->wo_flags & __WNOTHREAD) && wait->private != p->parent)
                return 0;

        return default_wake_function(wait, mode, sync, key);
}

void __wake_up_parent(struct task_struct *p, struct task_struct *parent)
{
        __wake_up_sync_key(&parent->signal->wait_chldexit,
                           TASK_INTERRUPTIBLE, p);
}

static bool is_effectively_child(struct wait_opts *wo, bool ptrace,
                                 struct task_struct *target)
{
        struct task_struct *parent =
                !ptrace ? target->real_parent : target->parent;

        return current == parent || (!(wo->wo_flags & __WNOTHREAD) &&
                                     same_thread_group(current, parent));
}

/*
 * Optimization for waiting on PIDTYPE_PID. No need to iterate through child
 * and tracee lists to find the target task.
 */
static int do_wait_pid(struct wait_opts *wo)
{
        bool ptrace;
        struct task_struct *target;
        int retval;

        ptrace = false;
        target = pid_task(wo->wo_pid, PIDTYPE_TGID);
        if (target && is_effectively_child(wo, ptrace, target)) {
                retval = wait_consider_task(wo, ptrace, target);
                if (retval)
                        return retval;
        }

        ptrace = true;
        target = pid_task(wo->wo_pid, PIDTYPE_PID);
        if (target && target->ptrace &&
            is_effectively_child(wo, ptrace, target)) {
                retval = wait_consider_task(wo, ptrace, target);
                if (retval)
                        return retval;
        }

        return 0;
}

static long do_wait(struct wait_opts *wo)
{
        int retval;

        trace_sched_process_wait(wo->wo_pid);

        init_waitqueue_func_entry(&wo->child_wait, child_wait_callback);
        wo->child_wait.private = current;
        add_wait_queue(&current->signal->wait_chldexit, &wo->child_wait);
repeat:
        /*
         * If there is nothing that can match our criteria, just get out.
         * We will clear ->notask_error to zero if we see any child that
         * might later match our criteria, even if we are not able to reap
         * it yet.
         */
        wo->notask_error = -ECHILD;
        if ((wo->wo_type < PIDTYPE_MAX) &&
           (!wo->wo_pid || !pid_has_task(wo->wo_pid, wo->wo_type)))
                goto notask;

        set_current_state(TASK_INTERRUPTIBLE);
        read_lock(&tasklist_lock);

        if (wo->wo_type == PIDTYPE_PID) {
                retval = do_wait_pid(wo);
                if (retval)
                        goto end;
        } else {
                struct task_struct *tsk = current;

                do {
                        retval = do_wait_thread(wo, tsk);
                        if (retval)
                                goto end;

                        retval = ptrace_do_wait(wo, tsk);
                        if (retval)
                                goto end;

                        if (wo->wo_flags & __WNOTHREAD)
                                break;
                } while_each_thread(current, tsk);
        }
        read_unlock(&tasklist_lock);

notask:
        retval = wo->notask_error;
        if (!retval && !(wo->wo_flags & WNOHANG)) {
                retval = -ERESTARTSYS;
                if (!signal_pending(current)) {
                        schedule();
                        goto repeat;
                }
        }
end:
        __set_current_state(TASK_RUNNING);
        remove_wait_queue(&current->signal->wait_chldexit, &wo->child_wait);
        return retval;
}

static long kernel_waitid(int which, pid_t upid, struct waitid_info *infop,
                          int options, struct rusage *ru)
{
        struct wait_opts wo;
        struct pid *pid = NULL;
        enum pid_type type;
        long ret;
        unsigned int f_flags = 0;

        if (options & ~(WNOHANG|WNOWAIT|WEXITED|WSTOPPED|WCONTINUED|
                        __WNOTHREAD|__WCLONE|__WALL))
                return -EINVAL;
        if (!(options & (WEXITED|WSTOPPED|WCONTINUED)))
                return -EINVAL;

        switch (which) {
        case P_ALL:
                type = PIDTYPE_MAX;
                break;
        case P_PID:
                type = PIDTYPE_PID;
                if (upid <= 0)
                        return -EINVAL;

                pid = find_get_pid(upid);
                break;
        case P_PGID:
                type = PIDTYPE_PGID;
                if (upid < 0)
                        return -EINVAL;

                if (upid)
                        pid = find_get_pid(upid);
                else
                        pid = get_task_pid(current, PIDTYPE_PGID);
                break;
        case P_PIDFD:
                type = PIDTYPE_PID;
                if (upid < 0)
                        return -EINVAL;

                pid = pidfd_get_pid(upid, &f_flags);
                if (IS_ERR(pid))
                        return PTR_ERR(pid);

                break;
        default:
                return -EINVAL;
        }

        wo.wo_type      = type;
        wo.wo_pid       = pid;
        wo.wo_flags     = options;
        wo.wo_info      = infop;
        wo.wo_rusage    = ru;
        if (f_flags & O_NONBLOCK)
                wo.wo_flags |= WNOHANG;

        ret = do_wait(&wo);
        if (!ret && !(options & WNOHANG) && (f_flags & O_NONBLOCK))
                ret = -EAGAIN;

        put_pid(pid);
        return ret;
}

SYSCALL_DEFINE5(waitid, int, which, pid_t, upid, struct siginfo __user *,
                infop, int, options, struct rusage __user *, ru)
{
        struct rusage r;
        struct waitid_info info = {.status = 0};
        long err = kernel_waitid(which, upid, &info, options, ru ? &r : NULL);
        int signo = 0;

        if (err > 0) {
                signo = SIGCHLD;
                err = 0;
                if (ru && copy_to_user(ru, &r, sizeof(struct rusage)))
                        return -EFAULT;
        }
        if (!infop)
                return err;

        if (!user_write_access_begin(infop, sizeof(*infop)))
                return -EFAULT;

        unsafe_put_user(signo, &infop->si_signo, Efault);
        unsafe_put_user(0, &infop->si_errno, Efault);
        unsafe_put_user(info.cause, &infop->si_code, Efault);
        unsafe_put_user(info.pid, &infop->si_pid, Efault);
        unsafe_put_user(info.uid, &infop->si_uid, Efault);
        unsafe_put_user(info.status, &infop->si_status, Efault);
        user_write_access_end();
        return err;
Efault:
        user_write_access_end();
        return -EFAULT;
}

long kernel_wait4(pid_t upid, int __user *stat_addr, int options,
                  struct rusage *ru)
{
        struct wait_opts wo;
        struct pid *pid = NULL;
        enum pid_type type;
        long ret;

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

        /* -INT_MIN is not defined */
        if (upid == INT_MIN)
                return -ESRCH;

        if (upid == -1)
                type = PIDTYPE_MAX;
        else if (upid < 0) {
                type = PIDTYPE_PGID;
                pid = find_get_pid(-upid);
        } else if (upid == 0) {
                type = PIDTYPE_PGID;
                pid = get_task_pid(current, PIDTYPE_PGID);
        } else /* upid > 0 */ {
                type = PIDTYPE_PID;
                pid = find_get_pid(upid);
        }

        wo.wo_type      = type;
        wo.wo_pid       = pid;
        wo.wo_flags     = options | WEXITED;
        wo.wo_info      = NULL;
        wo.wo_stat      = 0;
        wo.wo_rusage    = ru;
        ret = do_wait(&wo);
        put_pid(pid);
        if (ret > 0 && stat_addr && put_user(wo.wo_stat, stat_addr))
                ret = -EFAULT;

        return ret;
}

int kernel_wait(pid_t pid, int *stat)
{
        struct wait_opts wo = {
                .wo_type        = PIDTYPE_PID,
                .wo_pid         = find_get_pid(pid),
                .wo_flags       = WEXITED,
        };
        int ret;

        ret = do_wait(&wo);
        if (ret > 0 && wo.wo_stat)
                *stat = wo.wo_stat;
        put_pid(wo.wo_pid);
        return ret;
}

SYSCALL_DEFINE4(wait4, pid_t, upid, int __user *, stat_addr,
                int, options, struct rusage __user *, ru)
{
        struct rusage r;
        long err = kernel_wait4(upid, stat_addr, options, ru ? &r : NULL);

        if (err > 0) {
                if (ru && copy_to_user(ru, &r, sizeof(struct rusage)))
                        return -EFAULT;
        }
        return err;
}

#ifdef __ARCH_WANT_SYS_WAITPID

/*
 * sys_waitpid() remains for compatibility. waitpid() should be
 * implemented by calling sys_wait4() from libc.a.
 */
SYSCALL_DEFINE3(waitpid, pid_t, pid, int __user *, stat_addr, int, options)
{
        return kernel_wait4(pid, stat_addr, options, NULL);
}

#endif

#ifdef CONFIG_COMPAT
COMPAT_SYSCALL_DEFINE4(wait4,
        compat_pid_t, pid,
        compat_uint_t __user *, stat_addr,
        int, options,
        struct compat_rusage __user *, ru)
{
        struct rusage r;
        long err = kernel_wait4(pid, stat_addr, options, ru ? &r : NULL);
        if (err > 0) {
                if (ru && put_compat_rusage(&r, ru))
                        return -EFAULT;
        }
        return err;
}

COMPAT_SYSCALL_DEFINE5(waitid,
                int, which, compat_pid_t, pid,
                struct compat_siginfo __user *, infop, int, options,
                struct compat_rusage __user *, uru)
{
        struct rusage ru;
        struct waitid_info info = {.status = 0};
        long err = kernel_waitid(which, pid, &info, options, uru ? &ru : NULL);
        int signo = 0;
        if (err > 0) {
                signo = SIGCHLD;
                err = 0;
                if (uru) {
                        /* kernel_waitid() overwrites everything in ru */
                        if (COMPAT_USE_64BIT_TIME)
                                err = copy_to_user(uru, &ru, sizeof(ru));
                        else
                                err = put_compat_rusage(&ru, uru);
                        if (err)
                                return -EFAULT;
                }
        }

        if (!infop)
                return err;

        if (!user_write_access_begin(infop, sizeof(*infop)))
                return -EFAULT;

        unsafe_put_user(signo, &infop->si_signo, Efault);
        unsafe_put_user(0, &infop->si_errno, Efault);
        unsafe_put_user(info.cause, &infop->si_code, Efault);
        unsafe_put_user(info.pid, &infop->si_pid, Efault);
        unsafe_put_user(info.uid, &infop->si_uid, Efault);
        unsafe_put_user(info.status, &infop->si_status, Efault);
        user_write_access_end();
        return err;
Efault:
        user_write_access_end();
        return -EFAULT;
}
#endif

/**
 * thread_group_exited - check that a thread group has exited
 * @pid: tgid of thread group to be checked.
 *
 * Test if the thread group represented by tgid has exited (all
 * threads are zombies, dead or completely gone).
 *
 * Return: true if the thread group has exited. false otherwise.
 */
bool thread_group_exited(struct pid *pid)
{
        struct task_struct *task;
        bool exited;

        rcu_read_lock();
        task = pid_task(pid, PIDTYPE_PID);
        exited = !task ||
                (READ_ONCE(task->exit_state) && thread_group_empty(task));
        rcu_read_unlock();

        return exited;
}
EXPORT_SYMBOL(thread_group_exited);

__weak void abort(void)
{
        BUG();

        /* if that doesn't kill us, halt */
        panic("Oops failed to kill thread");
}
EXPORT_SYMBOL(abort);