Merge branch 'bugfixes' of git://git.linux-nfs.org/projects/trondmy/nfs-2.6

[pandora-kernel.git] / kernel / signal.c

/*
 *  linux/kernel/signal.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  1997-11-02  Modified for POSIX.1b signals by Richard Henderson
 *
 *  2003-06-02  Jim Houston - Concurrent Computer Corp.
 *              Changes to use preallocated sigqueue structures
 *              to allow signals to be sent reliably.
 */

#include <linux/slab.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/tty.h>
#include <linux/binfmts.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/ptrace.h>
#include <linux/signal.h>
#include <linux/signalfd.h>
#include <linux/ratelimit.h>
#include <linux/tracehook.h>
#include <linux/capability.h>
#include <linux/freezer.h>
#include <linux/pid_namespace.h>
#include <linux/nsproxy.h>
#define CREATE_TRACE_POINTS
#include <trace/events/signal.h>

#include <asm/param.h>
#include <asm/uaccess.h>
#include <asm/unistd.h>
#include <asm/siginfo.h>
#include "audit.h"      /* audit_signal_info() */

/*
 * SLAB caches for signal bits.
 */

static struct kmem_cache *sigqueue_cachep;

int print_fatal_signals __read_mostly;

static void __user *sig_handler(struct task_struct *t, int sig)
{
        return t->sighand->action[sig - 1].sa.sa_handler;
}

static int sig_handler_ignored(void __user *handler, int sig)
{
        /* Is it explicitly or implicitly ignored? */
        return handler == SIG_IGN ||
                (handler == SIG_DFL && sig_kernel_ignore(sig));
}

static int sig_task_ignored(struct task_struct *t, int sig,
                int from_ancestor_ns)
{
        void __user *handler;

        handler = sig_handler(t, sig);

        if (unlikely(t->signal->flags & SIGNAL_UNKILLABLE) &&
                        handler == SIG_DFL && !from_ancestor_ns)
                return 1;

        return sig_handler_ignored(handler, sig);
}

static int sig_ignored(struct task_struct *t, int sig, int from_ancestor_ns)
{
        /*
         * Blocked signals are never ignored, since the
         * signal handler may change by the time it is
         * unblocked.
         */
        if (sigismember(&t->blocked, sig) || sigismember(&t->real_blocked, sig))
                return 0;

        if (!sig_task_ignored(t, sig, from_ancestor_ns))
                return 0;

        /*
         * Tracers may want to know about even ignored signals.
         */
        return !tracehook_consider_ignored_signal(t, sig);
}

/*
 * Re-calculate pending state from the set of locally pending
 * signals, globally pending signals, and blocked signals.
 */
static inline int has_pending_signals(sigset_t *signal, sigset_t *blocked)
{
        unsigned long ready;
        long i;

        switch (_NSIG_WORDS) {
        default:
                for (i = _NSIG_WORDS, ready = 0; --i >= 0 ;)
                        ready |= signal->sig[i] &~ blocked->sig[i];
                break;

        case 4: ready  = signal->sig[3] &~ blocked->sig[3];
                ready |= signal->sig[2] &~ blocked->sig[2];
                ready |= signal->sig[1] &~ blocked->sig[1];
                ready |= signal->sig[0] &~ blocked->sig[0];
                break;

        case 2: ready  = signal->sig[1] &~ blocked->sig[1];
                ready |= signal->sig[0] &~ blocked->sig[0];
                break;

        case 1: ready  = signal->sig[0] &~ blocked->sig[0];
        }
        return ready != 0;
}

#define PENDING(p,b) has_pending_signals(&(p)->signal, (b))

static int recalc_sigpending_tsk(struct task_struct *t)
{
        if (t->signal->group_stop_count > 0 ||
            PENDING(&t->pending, &t->blocked) ||
            PENDING(&t->signal->shared_pending, &t->blocked)) {
                set_tsk_thread_flag(t, TIF_SIGPENDING);
                return 1;
        }
        /*
         * We must never clear the flag in another thread, or in current
         * when it's possible the current syscall is returning -ERESTART*.
         * So we don't clear it here, and only callers who know they should do.
         */
        return 0;
}

/*
 * After recalculating TIF_SIGPENDING, we need to make sure the task wakes up.
 * This is superfluous when called on current, the wakeup is a harmless no-op.
 */
void recalc_sigpending_and_wake(struct task_struct *t)
{
        if (recalc_sigpending_tsk(t))
                signal_wake_up(t, 0);
}

void recalc_sigpending(void)
{
        if (unlikely(tracehook_force_sigpending()))
                set_thread_flag(TIF_SIGPENDING);
        else if (!recalc_sigpending_tsk(current) && !freezing(current))
                clear_thread_flag(TIF_SIGPENDING);

}

/* Given the mask, find the first available signal that should be serviced. */

#define SYNCHRONOUS_MASK \
        (sigmask(SIGSEGV) | sigmask(SIGBUS) | sigmask(SIGILL) | \
         sigmask(SIGTRAP) | sigmask(SIGFPE))

int next_signal(struct sigpending *pending, sigset_t *mask)
{
        unsigned long i, *s, *m, x;
        int sig = 0;

        s = pending->signal.sig;
        m = mask->sig;

        /*
         * Handle the first word specially: it contains the
         * synchronous signals that need to be dequeued first.
         */
        x = *s &~ *m;
        if (x) {
                if (x & SYNCHRONOUS_MASK)
                        x &= SYNCHRONOUS_MASK;
                sig = ffz(~x) + 1;
                return sig;
        }

        switch (_NSIG_WORDS) {
        default:
                for (i = 1; i < _NSIG_WORDS; ++i) {
                        x = *++s &~ *++m;
                        if (!x)
                                continue;
                        sig = ffz(~x) + i*_NSIG_BPW + 1;
                        break;
                }
                break;

        case 2:
                x = s[1] &~ m[1];
                if (!x)
                        break;
                sig = ffz(~x) + _NSIG_BPW + 1;
                break;

        case 1:
                /* Nothing to do */
                break;
        }

        return sig;
}

static inline void print_dropped_signal(int sig)
{
        static DEFINE_RATELIMIT_STATE(ratelimit_state, 5 * HZ, 10);

        if (!print_fatal_signals)
                return;

        if (!__ratelimit(&ratelimit_state))
                return;

        printk(KERN_INFO "%s/%d: reached RLIMIT_SIGPENDING, dropped signal %d\n",
                                current->comm, current->pid, sig);
}

/*
 * allocate a new signal queue record
 * - this may be called without locks if and only if t == current, otherwise an
 *   appropriate lock must be held to stop the target task from exiting
 */
static struct sigqueue *
__sigqueue_alloc(int sig, struct task_struct *t, gfp_t flags, int override_rlimit)
{
        struct sigqueue *q = NULL;
        struct user_struct *user;

        /*
         * Protect access to @t credentials. This can go away when all
         * callers hold rcu read lock.
         */
        rcu_read_lock();
        user = get_uid(__task_cred(t)->user);
        atomic_inc(&user->sigpending);
        rcu_read_unlock();

        if (override_rlimit ||
            atomic_read(&user->sigpending) <=
                        task_rlimit(t, RLIMIT_SIGPENDING)) {
                q = kmem_cache_alloc(sigqueue_cachep, flags);
        } else {
                print_dropped_signal(sig);
        }

        if (unlikely(q == NULL)) {
                atomic_dec(&user->sigpending);
                free_uid(user);
        } else {
                INIT_LIST_HEAD(&q->list);
                q->flags = 0;
                q->user = user;
        }

        return q;
}

static void __sigqueue_free(struct sigqueue *q)
{
        if (q->flags & SIGQUEUE_PREALLOC)
                return;
        atomic_dec(&q->user->sigpending);
        free_uid(q->user);
        kmem_cache_free(sigqueue_cachep, q);
}

void flush_sigqueue(struct sigpending *queue)
{
        struct sigqueue *q;

        sigemptyset(&queue->signal);
        while (!list_empty(&queue->list)) {
                q = list_entry(queue->list.next, struct sigqueue , list);
                list_del_init(&q->list);
                __sigqueue_free(q);
        }
}

/*
 * Flush all pending signals for a task.
 */
void __flush_signals(struct task_struct *t)
{
        clear_tsk_thread_flag(t, TIF_SIGPENDING);
        flush_sigqueue(&t->pending);
        flush_sigqueue(&t->signal->shared_pending);
}

void flush_signals(struct task_struct *t)
{
        unsigned long flags;

        spin_lock_irqsave(&t->sighand->siglock, flags);
        __flush_signals(t);
        spin_unlock_irqrestore(&t->sighand->siglock, flags);
}

static void __flush_itimer_signals(struct sigpending *pending)
{
        sigset_t signal, retain;
        struct sigqueue *q, *n;

        signal = pending->signal;
        sigemptyset(&retain);

        list_for_each_entry_safe(q, n, &pending->list, list) {
                int sig = q->info.si_signo;

                if (likely(q->info.si_code != SI_TIMER)) {
                        sigaddset(&retain, sig);
                } else {
                        sigdelset(&signal, sig);
                        list_del_init(&q->list);
                        __sigqueue_free(q);
                }
        }

        sigorsets(&pending->signal, &signal, &retain);
}

void flush_itimer_signals(void)
{
        struct task_struct *tsk = current;
        unsigned long flags;

        spin_lock_irqsave(&tsk->sighand->siglock, flags);
        __flush_itimer_signals(&tsk->pending);
        __flush_itimer_signals(&tsk->signal->shared_pending);
        spin_unlock_irqrestore(&tsk->sighand->siglock, flags);
}

void ignore_signals(struct task_struct *t)
{
        int i;

        for (i = 0; i < _NSIG; ++i)
                t->sighand->action[i].sa.sa_handler = SIG_IGN;

        flush_signals(t);
}

/*
 * Flush all handlers for a task.
 */

void
flush_signal_handlers(struct task_struct *t, int force_default)
{
        int i;
        struct k_sigaction *ka = &t->sighand->action[0];
        for (i = _NSIG ; i != 0 ; i--) {
                if (force_default || ka->sa.sa_handler != SIG_IGN)
                        ka->sa.sa_handler = SIG_DFL;
                ka->sa.sa_flags = 0;
                sigemptyset(&ka->sa.sa_mask);
                ka++;
        }
}

int unhandled_signal(struct task_struct *tsk, int sig)
{
        void __user *handler = tsk->sighand->action[sig-1].sa.sa_handler;
        if (is_global_init(tsk))
                return 1;
        if (handler != SIG_IGN && handler != SIG_DFL)
                return 0;
        return !tracehook_consider_fatal_signal(tsk, sig);
}

/*
 * Notify the system that a driver wants to block all signals for this
 * process, and wants to be notified if any signals at all were to be
 * sent/acted upon.  If the notifier routine returns non-zero, then the
 * signal will be acted upon after all.  If the notifier routine returns 0,
 * then then signal will be blocked.  Only one block per process is
 * allowed.  priv is a pointer to private data that the notifier routine
 * can use to determine if the signal should be blocked or not.
 */
void
block_all_signals(int (*notifier)(void *priv), void *priv, sigset_t *mask)
{
        unsigned long flags;

        spin_lock_irqsave(&current->sighand->siglock, flags);
        current->notifier_mask = mask;
        current->notifier_data = priv;
        current->notifier = notifier;
        spin_unlock_irqrestore(&current->sighand->siglock, flags);
}

/* Notify the system that blocking has ended. */

void
unblock_all_signals(void)
{
        unsigned long flags;

        spin_lock_irqsave(&current->sighand->siglock, flags);
        current->notifier = NULL;
        current->notifier_data = NULL;
        recalc_sigpending();
        spin_unlock_irqrestore(&current->sighand->siglock, flags);
}

static void collect_signal(int sig, struct sigpending *list, siginfo_t *info)
{
        struct sigqueue *q, *first = NULL;

        /*
         * Collect the siginfo appropriate to this signal.  Check if
         * there is another siginfo for the same signal.
        */
        list_for_each_entry(q, &list->list, list) {
                if (q->info.si_signo == sig) {
                        if (first)
                                goto still_pending;
                        first = q;
                }
        }

        sigdelset(&list->signal, sig);

        if (first) {
still_pending:
                list_del_init(&first->list);
                copy_siginfo(info, &first->info);
                __sigqueue_free(first);
        } else {
                /*
                 * Ok, it wasn't in the queue.  This must be
                 * a fast-pathed signal or we must have been
                 * out of queue space.  So zero out the info.
                 */
                info->si_signo = sig;
                info->si_errno = 0;
                info->si_code = SI_USER;
                info->si_pid = 0;
                info->si_uid = 0;
        }
}

static int __dequeue_signal(struct sigpending *pending, sigset_t *mask,
                        siginfo_t *info)
{
        int sig = next_signal(pending, mask);

        if (sig) {
                if (current->notifier) {
                        if (sigismember(current->notifier_mask, sig)) {
                                if (!(current->notifier)(current->notifier_data)) {
                                        clear_thread_flag(TIF_SIGPENDING);
                                        return 0;
                                }
                        }
                }

                collect_signal(sig, pending, info);
        }

        return sig;
}

/*
 * Dequeue a signal and return the element to the caller, which is
 * expected to free it.
 *
 * All callers have to hold the siglock.
 */
int dequeue_signal(struct task_struct *tsk, sigset_t *mask, siginfo_t *info)
{
        int signr;

        /* We only dequeue private signals from ourselves, we don't let
         * signalfd steal them
         */
        signr = __dequeue_signal(&tsk->pending, mask, info);
        if (!signr) {
                signr = __dequeue_signal(&tsk->signal->shared_pending,
                                         mask, info);
                /*
                 * itimer signal ?
                 *
                 * itimers are process shared and we restart periodic
                 * itimers in the signal delivery path to prevent DoS
                 * attacks in the high resolution timer case. This is
                 * compliant with the old way of self-restarting
                 * itimers, as the SIGALRM is a legacy signal and only
                 * queued once. Changing the restart behaviour to
                 * restart the timer in the signal dequeue path is
                 * reducing the timer noise on heavy loaded !highres
                 * systems too.
                 */
                if (unlikely(signr == SIGALRM)) {
                        struct hrtimer *tmr = &tsk->signal->real_timer;

                        if (!hrtimer_is_queued(tmr) &&
                            tsk->signal->it_real_incr.tv64 != 0) {
                                hrtimer_forward(tmr, tmr->base->get_time(),
                                                tsk->signal->it_real_incr);
                                hrtimer_restart(tmr);
                        }
                }
        }

        recalc_sigpending();
        if (!signr)
                return 0;

        if (unlikely(sig_kernel_stop(signr))) {
                /*
                 * Set a marker that we have dequeued a stop signal.  Our
                 * caller might release the siglock and then the pending
                 * stop signal it is about to process is no longer in the
                 * pending bitmasks, but must still be cleared by a SIGCONT
                 * (and overruled by a SIGKILL).  So those cases clear this
                 * shared flag after we've set it.  Note that this flag may
                 * remain set after the signal we return is ignored or
                 * handled.  That doesn't matter because its only purpose
                 * is to alert stop-signal processing code when another
                 * processor has come along and cleared the flag.
                 */
                tsk->signal->flags |= SIGNAL_STOP_DEQUEUED;
        }
        if ((info->si_code & __SI_MASK) == __SI_TIMER && info->si_sys_private) {
                /*
                 * Release the siglock to ensure proper locking order
                 * of timer locks outside of siglocks.  Note, we leave
                 * irqs disabled here, since the posix-timers code is
                 * about to disable them again anyway.
                 */
                spin_unlock(&tsk->sighand->siglock);
                do_schedule_next_timer(info);
                spin_lock(&tsk->sighand->siglock);
        }
        return signr;
}

/*
 * Tell a process that it has a new active signal..
 *
 * NOTE! we rely on the previous spin_lock to
 * lock interrupts for us! We can only be called with
 * "siglock" held, and the local interrupt must
 * have been disabled when that got acquired!
 *
 * No need to set need_resched since signal event passing
 * goes through ->blocked
 */
void signal_wake_up(struct task_struct *t, int resume)
{
        unsigned int mask;

        set_tsk_thread_flag(t, TIF_SIGPENDING);

        /*
         * For SIGKILL, we want to wake it up in the stopped/traced/killable
         * case. We don't check t->state here because there is a race with it
         * executing another processor and just now entering stopped state.
         * By using wake_up_state, we ensure the process will wake up and
         * handle its death signal.
         */
        mask = TASK_INTERRUPTIBLE;
        if (resume)
                mask |= TASK_WAKEKILL;
        if (!wake_up_state(t, mask))
                kick_process(t);
}

/*
 * Remove signals in mask from the pending set and queue.
 * Returns 1 if any signals were found.
 *
 * All callers must be holding the siglock.
 *
 * This version takes a sigset mask and looks at all signals,
 * not just those in the first mask word.
 */
static int rm_from_queue_full(sigset_t *mask, struct sigpending *s)
{
        struct sigqueue *q, *n;
        sigset_t m;

        sigandsets(&m, mask, &s->signal);
        if (sigisemptyset(&m))
                return 0;

        signandsets(&s->signal, &s->signal, mask);
        list_for_each_entry_safe(q, n, &s->list, list) {
                if (sigismember(mask, q->info.si_signo)) {
                        list_del_init(&q->list);
                        __sigqueue_free(q);
                }
        }
        return 1;
}
/*
 * Remove signals in mask from the pending set and queue.
 * Returns 1 if any signals were found.
 *
 * All callers must be holding the siglock.
 */
static int rm_from_queue(unsigned long mask, struct sigpending *s)
{
        struct sigqueue *q, *n;

        if (!sigtestsetmask(&s->signal, mask))
                return 0;

        sigdelsetmask(&s->signal, mask);
        list_for_each_entry_safe(q, n, &s->list, list) {
                if (q->info.si_signo < SIGRTMIN &&
                    (mask & sigmask(q->info.si_signo))) {
                        list_del_init(&q->list);
                        __sigqueue_free(q);
                }
        }
        return 1;
}

static inline int is_si_special(const struct siginfo *info)
{
        return info <= SEND_SIG_FORCED;
}

static inline bool si_fromuser(const struct siginfo *info)
{
        return info == SEND_SIG_NOINFO ||
                (!is_si_special(info) && SI_FROMUSER(info));
}

/*
 * called with RCU read lock from check_kill_permission()
 */
static int kill_ok_by_cred(struct task_struct *t)
{
        const struct cred *cred = current_cred();
        const struct cred *tcred = __task_cred(t);

        if (cred->user->user_ns == tcred->user->user_ns &&
            (cred->euid == tcred->suid ||
             cred->euid == tcred->uid ||
             cred->uid  == tcred->suid ||
             cred->uid  == tcred->uid))
                return 1;

        if (ns_capable(tcred->user->user_ns, CAP_KILL))
                return 1;

        return 0;
}

/*
 * Bad permissions for sending the signal
 * - the caller must hold the RCU read lock
 */
static int check_kill_permission(int sig, struct siginfo *info,
                                 struct task_struct *t)
{
        struct pid *sid;
        int error;

        if (!valid_signal(sig))
                return -EINVAL;

        if (!si_fromuser(info))
                return 0;

        error = audit_signal_info(sig, t); /* Let audit system see the signal */
        if (error)
                return error;

        if (!same_thread_group(current, t) &&
            !kill_ok_by_cred(t)) {
                switch (sig) {
                case SIGCONT:
                        sid = task_session(t);
                        /*
                         * We don't return the error if sid == NULL. The
                         * task was unhashed, the caller must notice this.
                         */
                        if (!sid || sid == task_session(current))
                                break;
                default:
                        return -EPERM;
                }
        }

        return security_task_kill(t, info, sig, 0);
}

/*
 * Handle magic process-wide effects of stop/continue signals. Unlike
 * the signal actions, these happen immediately at signal-generation
 * time regardless of blocking, ignoring, or handling.  This does the
 * actual continuing for SIGCONT, but not the actual stopping for stop
 * signals. The process stop is done as a signal action for SIG_DFL.
 *
 * Returns true if the signal should be actually delivered, otherwise
 * it should be dropped.
 */
static int prepare_signal(int sig, struct task_struct *p, int from_ancestor_ns)
{
        struct signal_struct *signal = p->signal;
        struct task_struct *t;

        if (unlikely(signal->flags & SIGNAL_GROUP_EXIT)) {
                /*
                 * The process is in the middle of dying, nothing to do.
                 */
        } else if (sig_kernel_stop(sig)) {
                /*
                 * This is a stop signal.  Remove SIGCONT from all queues.
                 */
                rm_from_queue(sigmask(SIGCONT), &signal->shared_pending);
                t = p;
                do {
                        rm_from_queue(sigmask(SIGCONT), &t->pending);
                } while_each_thread(p, t);
        } else if (sig == SIGCONT) {
                unsigned int why;
                /*
                 * Remove all stop signals from all queues,
                 * and wake all threads.
                 */
                rm_from_queue(SIG_KERNEL_STOP_MASK, &signal->shared_pending);
                t = p;
                do {
                        unsigned int state;
                        rm_from_queue(SIG_KERNEL_STOP_MASK, &t->pending);
                        /*
                         * If there is a handler for SIGCONT, we must make
                         * sure that no thread returns to user mode before
                         * we post the signal, in case it was the only
                         * thread eligible to run the signal handler--then
                         * it must not do anything between resuming and
                         * running the handler.  With the TIF_SIGPENDING
                         * flag set, the thread will pause and acquire the
                         * siglock that we hold now and until we've queued
                         * the pending signal.
                         *
                         * Wake up the stopped thread _after_ setting
                         * TIF_SIGPENDING
                         */
                        state = __TASK_STOPPED;
                        if (sig_user_defined(t, SIGCONT) && !sigismember(&t->blocked, SIGCONT)) {
                                set_tsk_thread_flag(t, TIF_SIGPENDING);
                                state |= TASK_INTERRUPTIBLE;
                        }
                        wake_up_state(t, state);
                } while_each_thread(p, t);

                /*
                 * Notify the parent with CLD_CONTINUED if we were stopped.
                 *
                 * If we were in the middle of a group stop, we pretend it
                 * was already finished, and then continued. Since SIGCHLD
                 * doesn't queue we report only CLD_STOPPED, as if the next
                 * CLD_CONTINUED was dropped.
                 */
                why = 0;
                if (signal->flags & SIGNAL_STOP_STOPPED)
                        why |= SIGNAL_CLD_CONTINUED;
                else if (signal->group_stop_count)
                        why |= SIGNAL_CLD_STOPPED;

                if (why) {
                        /*
                         * The first thread which returns from do_signal_stop()
                         * will take ->siglock, notice SIGNAL_CLD_MASK, and
                         * notify its parent. See get_signal_to_deliver().
                         */
                        signal->flags = why | SIGNAL_STOP_CONTINUED;
                        signal->group_stop_count = 0;
                        signal->group_exit_code = 0;
                } else {
                        /*
                         * We are not stopped, but there could be a stop
                         * signal in the middle of being processed after
                         * being removed from the queue.  Clear that too.
                         */
                        signal->flags &= ~SIGNAL_STOP_DEQUEUED;
                }
        }

        return !sig_ignored(p, sig, from_ancestor_ns);
}

/*
 * Test if P wants to take SIG.  After we've checked all threads with this,
 * it's equivalent to finding no threads not blocking SIG.  Any threads not
 * blocking SIG were ruled out because they are not running and already
 * have pending signals.  Such threads will dequeue from the shared queue
 * as soon as they're available, so putting the signal on the shared queue
 * will be equivalent to sending it to one such thread.
 */
static inline int wants_signal(int sig, struct task_struct *p)
{
        if (sigismember(&p->blocked, sig))
                return 0;
        if (p->flags & PF_EXITING)
                return 0;
        if (sig == SIGKILL)
                return 1;
        if (task_is_stopped_or_traced(p))
                return 0;
        return task_curr(p) || !signal_pending(p);
}

static void complete_signal(int sig, struct task_struct *p, int group)
{
        struct signal_struct *signal = p->signal;
        struct task_struct *t;

        /*
         * Now find a thread we can wake up to take the signal off the queue.
         *
         * If the main thread wants the signal, it gets first crack.
         * Probably the least surprising to the average bear.
         */
        if (wants_signal(sig, p))
                t = p;
        else if (!group || thread_group_empty(p))
                /*
                 * There is just one thread and it does not need to be woken.
                 * It will dequeue unblocked signals before it runs again.
                 */
                return;
        else {
                /*
                 * Otherwise try to find a suitable thread.
                 */
                t = signal->curr_target;
                while (!wants_signal(sig, t)) {
                        t = next_thread(t);
                        if (t == signal->curr_target)
                                /*
                                 * No thread needs to be woken.
                                 * Any eligible threads will see
                                 * the signal in the queue soon.
                                 */
                                return;
                }
                signal->curr_target = t;
        }

        /*
         * Found a killable thread.  If the signal will be fatal,
         * then start taking the whole group down immediately.
         */
        if (sig_fatal(p, sig) &&
            !(signal->flags & (SIGNAL_UNKILLABLE | SIGNAL_GROUP_EXIT)) &&
            !sigismember(&t->real_blocked, sig) &&
            (sig == SIGKILL ||
             !tracehook_consider_fatal_signal(t, sig))) {
                /*
                 * This signal will be fatal to the whole group.
                 */
                if (!sig_kernel_coredump(sig)) {
                        /*
                         * Start a group exit and wake everybody up.
                         * This way we don't have other threads
                         * running and doing things after a slower
                         * thread has the fatal signal pending.
                         */
                        signal->flags = SIGNAL_GROUP_EXIT;
                        signal->group_exit_code = sig;
                        signal->group_stop_count = 0;
                        t = p;
                        do {
                                sigaddset(&t->pending.signal, SIGKILL);
                                signal_wake_up(t, 1);
                        } while_each_thread(p, t);
                        return;
                }
        }

        /*
         * The signal is already in the shared-pending queue.
         * Tell the chosen thread to wake up and dequeue it.
         */
        signal_wake_up(t, sig == SIGKILL);
        return;
}

static inline int legacy_queue(struct sigpending *signals, int sig)
{
        return (sig < SIGRTMIN) && sigismember(&signals->signal, sig);
}

static int __send_signal(int sig, struct siginfo *info, struct task_struct *t,
                        int group, int from_ancestor_ns)
{
        struct sigpending *pending;
        struct sigqueue *q;
        int override_rlimit;

        trace_signal_generate(sig, info, t);

        assert_spin_locked(&t->sighand->siglock);

        if (!prepare_signal(sig, t, from_ancestor_ns))
                return 0;

        pending = group ? &t->signal->shared_pending : &t->pending;
        /*
         * Short-circuit ignored signals and support queuing
         * exactly one non-rt signal, so that we can get more
         * detailed information about the cause of the signal.
         */
        if (legacy_queue(pending, sig))
                return 0;
        /*
         * fast-pathed signals for kernel-internal things like SIGSTOP
         * or SIGKILL.
         */
        if (info == SEND_SIG_FORCED)
                goto out_set;

        /*
         * Real-time signals must be queued if sent by sigqueue, or
         * some other real-time mechanism.  It is implementation
         * defined whether kill() does so.  We attempt to do so, on
         * the principle of least surprise, but since kill is not
         * allowed to fail with EAGAIN when low on memory we just
         * make sure at least one signal gets delivered and don't
         * pass on the info struct.
         */
        if (sig < SIGRTMIN)
                override_rlimit = (is_si_special(info) || info->si_code >= 0);
        else
                override_rlimit = 0;

        q = __sigqueue_alloc(sig, t, GFP_ATOMIC | __GFP_NOTRACK_FALSE_POSITIVE,
                override_rlimit);
        if (q) {
                list_add_tail(&q->list, &pending->list);
                switch ((unsigned long) info) {
                case (unsigned long) SEND_SIG_NOINFO:
                        q->info.si_signo = sig;
                        q->info.si_errno = 0;
                        q->info.si_code = SI_USER;
                        q->info.si_pid = task_tgid_nr_ns(current,
                                                        task_active_pid_ns(t));
                        q->info.si_uid = current_uid();
                        break;
                case (unsigned long) SEND_SIG_PRIV:
                        q->info.si_signo = sig;
                        q->info.si_errno = 0;
                        q->info.si_code = SI_KERNEL;
                        q->info.si_pid = 0;
                        q->info.si_uid = 0;
                        break;
                default:
                        copy_siginfo(&q->info, info);
                        if (from_ancestor_ns)
                                q->info.si_pid = 0;
                        break;
                }
        } else if (!is_si_special(info)) {
                if (sig >= SIGRTMIN && info->si_code != SI_USER) {
                        /*
                         * Queue overflow, abort.  We may abort if the
                         * signal was rt and sent by user using something
                         * other than kill().
                         */
                        trace_signal_overflow_fail(sig, group, info);
                        return -EAGAIN;
                } else {
                        /*
                         * This is a silent loss of information.  We still
                         * send the signal, but the *info bits are lost.
                         */
                        trace_signal_lose_info(sig, group, info);
                }
        }

out_set:
        signalfd_notify(t, sig);
        sigaddset(&pending->signal, sig);
        complete_signal(sig, t, group);
        return 0;
}

static int send_signal(int sig, struct siginfo *info, struct task_struct *t,
                        int group)
{
        int from_ancestor_ns = 0;

#ifdef CONFIG_PID_NS
        from_ancestor_ns = si_fromuser(info) &&
                           !task_pid_nr_ns(current, task_active_pid_ns(t));
#endif

        return __send_signal(sig, info, t, group, from_ancestor_ns);
}

static void print_fatal_signal(struct pt_regs *regs, int signr)
{
        printk("%s/%d: potentially unexpected fatal signal %d.\n",
                current->comm, task_pid_nr(current), signr);

#if defined(__i386__) && !defined(__arch_um__)
        printk("code at %08lx: ", regs->ip);
        {
                int i;
                for (i = 0; i < 16; i++) {
                        unsigned char insn;

                        if (get_user(insn, (unsigned char *)(regs->ip + i)))
                                break;
                        printk("%02x ", insn);
                }
        }
#endif
        printk("\n");
        preempt_disable();
        show_regs(regs);
        preempt_enable();
}

static int __init setup_print_fatal_signals(char *str)
{
        get_option (&str, &print_fatal_signals);

        return 1;
}

__setup("print-fatal-signals=", setup_print_fatal_signals);

int
__group_send_sig_info(int sig, struct siginfo *info, struct task_struct *p)
{
        return send_signal(sig, info, p, 1);
}

static int
specific_send_sig_info(int sig, struct siginfo *info, struct task_struct *t)
{
        return send_signal(sig, info, t, 0);
}

int do_send_sig_info(int sig, struct siginfo *info, struct task_struct *p,
                        bool group)
{
        unsigned long flags;
        int ret = -ESRCH;

        if (lock_task_sighand(p, &flags)) {
                ret = send_signal(sig, info, p, group);
                unlock_task_sighand(p, &flags);
        }

        return ret;
}

/*
 * Force a signal that the process can't ignore: if necessary
 * we unblock the signal and change any SIG_IGN to SIG_DFL.
 *
 * Note: If we unblock the signal, we always reset it to SIG_DFL,
 * since we do not want to have a signal handler that was blocked
 * be invoked when user space had explicitly blocked it.
 *
 * We don't want to have recursive SIGSEGV's etc, for example,
 * that is why we also clear SIGNAL_UNKILLABLE.
 */
int
force_sig_info(int sig, struct siginfo *info, struct task_struct *t)
{
        unsigned long int flags;
        int ret, blocked, ignored;
        struct k_sigaction *action;

        spin_lock_irqsave(&t->sighand->siglock, flags);
        action = &t->sighand->action[sig-1];
        ignored = action->sa.sa_handler == SIG_IGN;
        blocked = sigismember(&t->blocked, sig);
        if (blocked || ignored) {
                action->sa.sa_handler = SIG_DFL;
                if (blocked) {
                        sigdelset(&t->blocked, sig);
                        recalc_sigpending_and_wake(t);
                }
        }
        if (action->sa.sa_handler == SIG_DFL)
                t->signal->flags &= ~SIGNAL_UNKILLABLE;
        ret = specific_send_sig_info(sig, info, t);
        spin_unlock_irqrestore(&t->sighand->siglock, flags);

        return ret;
}

/*
 * Nuke all other threads in the group.
 */
int zap_other_threads(struct task_struct *p)
{
        struct task_struct *t = p;
        int count = 0;

        p->signal->group_stop_count = 0;

        while_each_thread(p, t) {
                count++;

                /* Don't bother with already dead threads */
                if (t->exit_state)
                        continue;
                sigaddset(&t->pending.signal, SIGKILL);
                signal_wake_up(t, 1);
        }

        return count;
}

struct sighand_struct *__lock_task_sighand(struct task_struct *tsk,
                                           unsigned long *flags)
{
        struct sighand_struct *sighand;

        rcu_read_lock();
        for (;;) {
                sighand = rcu_dereference(tsk->sighand);
                if (unlikely(sighand == NULL))
                        break;

                spin_lock_irqsave(&sighand->siglock, *flags);
                if (likely(sighand == tsk->sighand))
                        break;
                spin_unlock_irqrestore(&sighand->siglock, *flags);
        }
        rcu_read_unlock();

        return sighand;
}

/*
 * send signal info to all the members of a group
 */
int group_send_sig_info(int sig, struct siginfo *info, struct task_struct *p)
{
        int ret;

        rcu_read_lock();
        ret = check_kill_permission(sig, info, p);
        rcu_read_unlock();

        if (!ret && sig)
                ret = do_send_sig_info(sig, info, p, true);

        return ret;
}

/*
 * __kill_pgrp_info() sends a signal to a process group: this is what the tty
 * control characters do (^C, ^Z etc)
 * - the caller must hold at least a readlock on tasklist_lock
 */
int __kill_pgrp_info(int sig, struct siginfo *info, struct pid *pgrp)
{
        struct task_struct *p = NULL;
        int retval, success;

        success = 0;
        retval = -ESRCH;
        do_each_pid_task(pgrp, PIDTYPE_PGID, p) {
                int err = group_send_sig_info(sig, info, p);
                success |= !err;
                retval = err;
        } while_each_pid_task(pgrp, PIDTYPE_PGID, p);
        return success ? 0 : retval;
}

int kill_pid_info(int sig, struct siginfo *info, struct pid *pid)
{
        int error = -ESRCH;
        struct task_struct *p;

        rcu_read_lock();
retry:
        p = pid_task(pid, PIDTYPE_PID);
        if (p) {
                error = group_send_sig_info(sig, info, p);
                if (unlikely(error == -ESRCH))
                        /*
                         * The task was unhashed in between, try again.
                         * If it is dead, pid_task() will return NULL,
                         * if we race with de_thread() it will find the
                         * new leader.
                         */
                        goto retry;
        }
        rcu_read_unlock();

        return error;
}

int kill_proc_info(int sig, struct siginfo *info, pid_t pid)
{
        int error;
        rcu_read_lock();
        error = kill_pid_info(sig, info, find_vpid(pid));
        rcu_read_unlock();
        return error;
}

/* like kill_pid_info(), but doesn't use uid/euid of "current" */
int kill_pid_info_as_uid(int sig, struct siginfo *info, struct pid *pid,
                      uid_t uid, uid_t euid, u32 secid)
{
        int ret = -EINVAL;
        struct task_struct *p;
        const struct cred *pcred;
        unsigned long flags;

        if (!valid_signal(sig))
                return ret;

        rcu_read_lock();
        p = pid_task(pid, PIDTYPE_PID);
        if (!p) {
                ret = -ESRCH;
                goto out_unlock;
        }
        pcred = __task_cred(p);
        if (si_fromuser(info) &&
            euid != pcred->suid && euid != pcred->uid &&
            uid  != pcred->suid && uid  != pcred->uid) {
                ret = -EPERM;
                goto out_unlock;
        }
        ret = security_task_kill(p, info, sig, secid);
        if (ret)
                goto out_unlock;

        if (sig) {
                if (lock_task_sighand(p, &flags)) {
                        ret = __send_signal(sig, info, p, 1, 0);
                        unlock_task_sighand(p, &flags);
                } else
                        ret = -ESRCH;
        }
out_unlock:
        rcu_read_unlock();
        return ret;
}
EXPORT_SYMBOL_GPL(kill_pid_info_as_uid);

/*
 * kill_something_info() interprets pid in interesting ways just like kill(2).
 *
 * POSIX specifies that kill(-1,sig) is unspecified, but what we have
 * is probably wrong.  Should make it like BSD or SYSV.
 */

static int kill_something_info(int sig, struct siginfo *info, pid_t pid)
{
        int ret;

        if (pid > 0) {
                rcu_read_lock();
                ret = kill_pid_info(sig, info, find_vpid(pid));
                rcu_read_unlock();
                return ret;
        }

        read_lock(&tasklist_lock);
        if (pid != -1) {
                ret = __kill_pgrp_info(sig, info,
                                pid ? find_vpid(-pid) : task_pgrp(current));
        } else {
                int retval = 0, count = 0;
                struct task_struct * p;

                for_each_process(p) {
                        if (task_pid_vnr(p) > 1 &&
                                        !same_thread_group(p, current)) {
                                int err = group_send_sig_info(sig, info, p);
                                ++count;
                                if (err != -EPERM)
                                        retval = err;
                        }
                }
                ret = count ? retval : -ESRCH;
        }
        read_unlock(&tasklist_lock);

        return ret;
}

/*
 * These are for backward compatibility with the rest of the kernel source.
 */

int send_sig_info(int sig, struct siginfo *info, struct task_struct *p)
{
        /*
         * Make sure legacy kernel users don't send in bad values
         * (normal paths check this in check_kill_permission).
         */
        if (!valid_signal(sig))
                return -EINVAL;

        return do_send_sig_info(sig, info, p, false);
}

#define __si_special(priv) \
        ((priv) ? SEND_SIG_PRIV : SEND_SIG_NOINFO)

int
send_sig(int sig, struct task_struct *p, int priv)
{
        return send_sig_info(sig, __si_special(priv), p);
}

void
force_sig(int sig, struct task_struct *p)
{
        force_sig_info(sig, SEND_SIG_PRIV, p);
}

/*
 * When things go south during signal handling, we
 * will force a SIGSEGV. And if the signal that caused
 * the problem was already a SIGSEGV, we'll want to
 * make sure we don't even try to deliver the signal..
 */
int
force_sigsegv(int sig, struct task_struct *p)
{
        if (sig == SIGSEGV) {
                unsigned long flags;
                spin_lock_irqsave(&p->sighand->siglock, flags);
                p->sighand->action[sig - 1].sa.sa_handler = SIG_DFL;
                spin_unlock_irqrestore(&p->sighand->siglock, flags);
        }
        force_sig(SIGSEGV, p);
        return 0;
}

int kill_pgrp(struct pid *pid, int sig, int priv)
{
        int ret;

        read_lock(&tasklist_lock);
        ret = __kill_pgrp_info(sig, __si_special(priv), pid);
        read_unlock(&tasklist_lock);

        return ret;
}
EXPORT_SYMBOL(kill_pgrp);

int kill_pid(struct pid *pid, int sig, int priv)
{
        return kill_pid_info(sig, __si_special(priv), pid);
}
EXPORT_SYMBOL(kill_pid);

/*
 * These functions support sending signals using preallocated sigqueue
 * structures.  This is needed "because realtime applications cannot
 * afford to lose notifications of asynchronous events, like timer
 * expirations or I/O completions".  In the case of POSIX Timers
 * we allocate the sigqueue structure from the timer_create.  If this
 * allocation fails we are able to report the failure to the application
 * with an EAGAIN error.
 */
struct sigqueue *sigqueue_alloc(void)
{
        struct sigqueue *q = __sigqueue_alloc(-1, current, GFP_KERNEL, 0);

        if (q)
                q->flags |= SIGQUEUE_PREALLOC;

        return q;
}

void sigqueue_free(struct sigqueue *q)
{
        unsigned long flags;
        spinlock_t *lock = &current->sighand->siglock;

        BUG_ON(!(q->flags & SIGQUEUE_PREALLOC));
        /*
         * We must hold ->siglock while testing q->list
         * to serialize with collect_signal() or with
         * __exit_signal()->flush_sigqueue().
         */
        spin_lock_irqsave(lock, flags);
        q->flags &= ~SIGQUEUE_PREALLOC;
        /*
         * If it is queued it will be freed when dequeued,
         * like the "regular" sigqueue.
         */
        if (!list_empty(&q->list))
                q = NULL;
        spin_unlock_irqrestore(lock, flags);

        if (q)
                __sigqueue_free(q);
}

int send_sigqueue(struct sigqueue *q, struct task_struct *t, int group)
{
        int sig = q->info.si_signo;
        struct sigpending *pending;
        unsigned long flags;
        int ret;

        BUG_ON(!(q->flags & SIGQUEUE_PREALLOC));

        ret = -1;
        if (!likely(lock_task_sighand(t, &flags)))
                goto ret;

        ret = 1; /* the signal is ignored */
        if (!prepare_signal(sig, t, 0))
                goto out;

        ret = 0;
        if (unlikely(!list_empty(&q->list))) {
                /*
                 * If an SI_TIMER entry is already queue just increment
                 * the overrun count.
                 */
                BUG_ON(q->info.si_code != SI_TIMER);
                q->info.si_overrun++;
                goto out;
        }
        q->info.si_overrun = 0;

        signalfd_notify(t, sig);
        pending = group ? &t->signal->shared_pending : &t->pending;
        list_add_tail(&q->list, &pending->list);
        sigaddset(&pending->signal, sig);
        complete_signal(sig, t, group);
out:
        unlock_task_sighand(t, &flags);
ret:
        return ret;
}

/*
 * Let a parent know about the death of a child.
 * For a stopped/continued status change, use do_notify_parent_cldstop instead.
 *
 * Returns -1 if our parent ignored us and so we've switched to
 * self-reaping, or else @sig.
 */
int do_notify_parent(struct task_struct *tsk, int sig)
{
        struct siginfo info;
        unsigned long flags;
        struct sighand_struct *psig;
        int ret = sig;

        BUG_ON(sig == -1);

        /* do_notify_parent_cldstop should have been called instead.  */
        BUG_ON(task_is_stopped_or_traced(tsk));

        BUG_ON(!task_ptrace(tsk) &&
               (tsk->group_leader != tsk || !thread_group_empty(tsk)));

        info.si_signo = sig;
        info.si_errno = 0;
        /*
         * we are under tasklist_lock here so our parent is tied to
         * us and cannot exit and release its namespace.
         *
         * the only it can is to switch its nsproxy with sys_unshare,
         * bu uncharing pid namespaces is not allowed, so we'll always
         * see relevant namespace
         *
         * write_lock() currently calls preempt_disable() which is the
         * same as rcu_read_lock(), but according to Oleg, this is not
         * correct to rely on this
         */
        rcu_read_lock();
        info.si_pid = task_pid_nr_ns(tsk, tsk->parent->nsproxy->pid_ns);
        info.si_uid = __task_cred(tsk)->uid;
        rcu_read_unlock();

        info.si_utime = cputime_to_clock_t(cputime_add(tsk->utime,
                                tsk->signal->utime));
        info.si_stime = cputime_to_clock_t(cputime_add(tsk->stime,
                                tsk->signal->stime));

        info.si_status = tsk->exit_code & 0x7f;
        if (tsk->exit_code & 0x80)
                info.si_code = CLD_DUMPED;
        else if (tsk->exit_code & 0x7f)
                info.si_code = CLD_KILLED;
        else {
                info.si_code = CLD_EXITED;
                info.si_status = tsk->exit_code >> 8;
        }

        psig = tsk->parent->sighand;
        spin_lock_irqsave(&psig->siglock, flags);
        if (!task_ptrace(tsk) && sig == SIGCHLD &&
            (psig->action[SIGCHLD-1].sa.sa_handler == SIG_IGN ||
             (psig->action[SIGCHLD-1].sa.sa_flags & SA_NOCLDWAIT))) {
                /*
                 * We are exiting and our parent doesn't care.  POSIX.1
                 * defines special semantics for setting SIGCHLD to SIG_IGN
                 * or setting the SA_NOCLDWAIT flag: we should be reaped
                 * automatically and not left for our parent's wait4 call.
                 * Rather than having the parent do it as a magic kind of
                 * signal handler, we just set this to tell do_exit that we
                 * can be cleaned up without becoming a zombie.  Note that
                 * we still call __wake_up_parent in this case, because a
                 * blocked sys_wait4 might now return -ECHILD.
                 *
                 * Whether we send SIGCHLD or not for SA_NOCLDWAIT
                 * is implementation-defined: we do (if you don't want
                 * it, just use SIG_IGN instead).
                 */
                ret = tsk->exit_signal = -1;
                if (psig->action[SIGCHLD-1].sa.sa_handler == SIG_IGN)
                        sig = -1;
        }
        if (valid_signal(sig) && sig > 0)
                __group_send_sig_info(sig, &info, tsk->parent);
        __wake_up_parent(tsk, tsk->parent);
        spin_unlock_irqrestore(&psig->siglock, flags);

        return ret;
}

static void do_notify_parent_cldstop(struct task_struct *tsk, int why)
{
        struct siginfo info;
        unsigned long flags;
        struct task_struct *parent;
        struct sighand_struct *sighand;

        if (task_ptrace(tsk))
                parent = tsk->parent;
        else {
                tsk = tsk->group_leader;
                parent = tsk->real_parent;
        }

        info.si_signo = SIGCHLD;
        info.si_errno = 0;
        /*
         * see comment in do_notify_parent() about the following 4 lines
         */
        rcu_read_lock();
        info.si_pid = task_pid_nr_ns(tsk, parent->nsproxy->pid_ns);
        info.si_uid = __task_cred(tsk)->uid;
        rcu_read_unlock();

        info.si_utime = cputime_to_clock_t(tsk->utime);
        info.si_stime = cputime_to_clock_t(tsk->stime);

        info.si_code = why;
        switch (why) {
        case CLD_CONTINUED:
                info.si_status = SIGCONT;
                break;
        case CLD_STOPPED:
                info.si_status = tsk->signal->group_exit_code & 0x7f;
                break;
        case CLD_TRAPPED:
                info.si_status = tsk->exit_code & 0x7f;
                break;
        default:
                BUG();
        }

        sighand = parent->sighand;
        spin_lock_irqsave(&sighand->siglock, flags);
        if (sighand->action[SIGCHLD-1].sa.sa_handler != SIG_IGN &&
            !(sighand->action[SIGCHLD-1].sa.sa_flags & SA_NOCLDSTOP))
                __group_send_sig_info(SIGCHLD, &info, parent);
        /*
         * Even if SIGCHLD is not generated, we must wake up wait4 calls.
         */
        __wake_up_parent(tsk, parent);
        spin_unlock_irqrestore(&sighand->siglock, flags);
}

static inline int may_ptrace_stop(void)
{
        if (!likely(task_ptrace(current)))
                return 0;
        /*
         * Are we in the middle of do_coredump?
         * If so and our tracer is also part of the coredump stopping
         * is a deadlock situation, and pointless because our tracer
         * is dead so don't allow us to stop.
         * If SIGKILL was already sent before the caller unlocked
         * ->siglock we must see ->core_state != NULL. Otherwise it
         * is safe to enter schedule().
         */
        if (unlikely(current->mm->core_state) &&
            unlikely(current->mm == current->parent->mm))
                return 0;

        return 1;
}

/*
 * Return non-zero if there is a SIGKILL that should be waking us up.
 * Called with the siglock held.
 */
static int sigkill_pending(struct task_struct *tsk)
{
        return  sigismember(&tsk->pending.signal, SIGKILL) ||
                sigismember(&tsk->signal->shared_pending.signal, SIGKILL);
}

/*
 * This must be called with current->sighand->siglock held.
 *
 * This should be the path for all ptrace stops.
 * We always set current->last_siginfo while stopped here.
 * That makes it a way to test a stopped process for
 * being ptrace-stopped vs being job-control-stopped.
 *
 * If we actually decide not to stop at all because the tracer
 * is gone, we keep current->exit_code unless clear_code.
 */
static void ptrace_stop(int exit_code, int clear_code, siginfo_t *info)
        __releases(&current->sighand->siglock)
        __acquires(&current->sighand->siglock)
{
        if (arch_ptrace_stop_needed(exit_code, info)) {
                /*
                 * The arch code has something special to do before a
                 * ptrace stop.  This is allowed to block, e.g. for faults
                 * on user stack pages.  We can't keep the siglock while
                 * calling arch_ptrace_stop, so we must release it now.
                 * To preserve proper semantics, we must do this before
                 * any signal bookkeeping like checking group_stop_count.
                 * Meanwhile, a SIGKILL could come in before we retake the
                 * siglock.  That must prevent us from sleeping in TASK_TRACED.
                 * So after regaining the lock, we must check for SIGKILL.
                 */
                spin_unlock_irq(&current->sighand->siglock);
                arch_ptrace_stop(exit_code, info);
                spin_lock_irq(&current->sighand->siglock);
                if (sigkill_pending(current))
                        return;
        }

        /*
         * If there is a group stop in progress,
         * we must participate in the bookkeeping.
         */
        if (current->signal->group_stop_count > 0)
                --current->signal->group_stop_count;

        current->last_siginfo = info;
        current->exit_code = exit_code;

        /* Let the debugger run.  */
        __set_current_state(TASK_TRACED);
        spin_unlock_irq(&current->sighand->siglock);
        read_lock(&tasklist_lock);
        if (may_ptrace_stop()) {
                do_notify_parent_cldstop(current, CLD_TRAPPED);
                /*
                 * Don't want to allow preemption here, because
                 * sys_ptrace() needs this task to be inactive.
                 *
                 * XXX: implement read_unlock_no_resched().
                 */
                preempt_disable();
                read_unlock(&tasklist_lock);
                preempt_enable_no_resched();
                schedule();
        } else {
                /*
                 * By the time we got the lock, our tracer went away.
                 * Don't drop the lock yet, another tracer may come.
                 */
                __set_current_state(TASK_RUNNING);
                if (clear_code)
                        current->exit_code = 0;
                read_unlock(&tasklist_lock);
        }

        /*
         * While in TASK_TRACED, we were considered "frozen enough".
         * Now that we woke up, it's crucial if we're supposed to be
         * frozen that we freeze now before running anything substantial.
         */
        try_to_freeze();

        /*
         * We are back.  Now reacquire the siglock before touching
         * last_siginfo, so that we are sure to have synchronized with
         * any signal-sending on another CPU that wants to examine it.
         */
        spin_lock_irq(&current->sighand->siglock);
        current->last_siginfo = NULL;

        /*
         * Queued signals ignored us while we were stopped for tracing.
         * So check for any that we should take before resuming user mode.
         * This sets TIF_SIGPENDING, but never clears it.
         */
        recalc_sigpending_tsk(current);
}

void ptrace_notify(int exit_code)
{
        siginfo_t info;

        BUG_ON((exit_code & (0x7f | ~0xffff)) != SIGTRAP);

        memset(&info, 0, sizeof info);
        info.si_signo = SIGTRAP;
        info.si_code = exit_code;
        info.si_pid = task_pid_vnr(current);
        info.si_uid = current_uid();

        /* Let the debugger run.  */
        spin_lock_irq(&current->sighand->siglock);
        ptrace_stop(exit_code, 1, &info);
        spin_unlock_irq(&current->sighand->siglock);
}

/*
 * This performs the stopping for SIGSTOP and other stop signals.
 * We have to stop all threads in the thread group.
 * Returns non-zero if we've actually stopped and released the siglock.
 * Returns zero if we didn't stop and still hold the siglock.
 */
static int do_signal_stop(int signr)
{
        struct signal_struct *sig = current->signal;
        int notify;

        if (!sig->group_stop_count) {
                struct task_struct *t;

                if (!likely(sig->flags & SIGNAL_STOP_DEQUEUED) ||
                    unlikely(signal_group_exit(sig)))
                        return 0;
                /*
                 * There is no group stop already in progress.
                 * We must initiate one now.
                 */
                sig->group_exit_code = signr;

                sig->group_stop_count = 1;
                for (t = next_thread(current); t != current; t = next_thread(t))
                        /*
                         * Setting state to TASK_STOPPED for a group
                         * stop is always done with the siglock held,
                         * so this check has no races.
                         */
                        if (!(t->flags & PF_EXITING) &&
                            !task_is_stopped_or_traced(t)) {
                                sig->group_stop_count++;
                                signal_wake_up(t, 0);
                        }
        }
        /*
         * If there are no other threads in the group, or if there is
         * a group stop in progress and we are the last to stop, report
         * to the parent.  When ptraced, every thread reports itself.
         */
        notify = sig->group_stop_count == 1 ? CLD_STOPPED : 0;
        notify = tracehook_notify_jctl(notify, CLD_STOPPED);
        /*
         * tracehook_notify_jctl() can drop and reacquire siglock, so
         * we keep ->group_stop_count != 0 before the call. If SIGCONT
         * or SIGKILL comes in between ->group_stop_count == 0.
         */
        if (sig->group_stop_count) {
                if (!--sig->group_stop_count)
                        sig->flags = SIGNAL_STOP_STOPPED;
                current->exit_code = sig->group_exit_code;
                __set_current_state(TASK_STOPPED);
        }
        spin_unlock_irq(&current->sighand->siglock);

        if (notify) {
                read_lock(&tasklist_lock);
                do_notify_parent_cldstop(current, notify);
                read_unlock(&tasklist_lock);
        }

        /* Now we don't run again until woken by SIGCONT or SIGKILL */
        do {
                schedule();
        } while (try_to_freeze());

        tracehook_finish_jctl();
        current->exit_code = 0;

        return 1;
}

static int ptrace_signal(int signr, siginfo_t *info,
                         struct pt_regs *regs, void *cookie)
{
        if (!task_ptrace(current))
                return signr;

        ptrace_signal_deliver(regs, cookie);

        /* Let the debugger run.  */
        ptrace_stop(signr, 0, info);

        /* We're back.  Did the debugger cancel the sig?  */
        signr = current->exit_code;
        if (signr == 0)
                return signr;

        current->exit_code = 0;

        /*
         * Update the siginfo structure if the signal has
         * changed.  If the debugger wanted something
         * specific in the siginfo structure then it should
         * have updated *info via PTRACE_SETSIGINFO.
         */
        if (signr != info->si_signo) {
                info->si_signo = signr;
                info->si_errno = 0;
                info->si_code = SI_USER;
                info->si_pid = task_pid_vnr(current->parent);
                info->si_uid = task_uid(current->parent);
        }

        /* If the (new) signal is now blocked, requeue it.  */
        if (sigismember(&current->blocked, signr)) {
                specific_send_sig_info(signr, info, current);
                signr = 0;
        }

        return signr;
}

int get_signal_to_deliver(siginfo_t *info, struct k_sigaction *return_ka,
                          struct pt_regs *regs, void *cookie)
{
        struct sighand_struct *sighand = current->sighand;
        struct signal_struct *signal = current->signal;
        int signr;

relock:
        /*
         * We'll jump back here after any time we were stopped in TASK_STOPPED.
         * While in TASK_STOPPED, we were considered "frozen enough".
         * Now that we woke up, it's crucial if we're supposed to be
         * frozen that we freeze now before running anything substantial.
         */
        try_to_freeze();

        spin_lock_irq(&sighand->siglock);
        /*
         * Every stopped thread goes here after wakeup. Check to see if
         * we should notify the parent, prepare_signal(SIGCONT) encodes
         * the CLD_ si_code into SIGNAL_CLD_MASK bits.
         */
        if (unlikely(signal->flags & SIGNAL_CLD_MASK)) {
                int why = (signal->flags & SIGNAL_STOP_CONTINUED)
                                ? CLD_CONTINUED : CLD_STOPPED;
                signal->flags &= ~SIGNAL_CLD_MASK;

                why = tracehook_notify_jctl(why, CLD_CONTINUED);
                spin_unlock_irq(&sighand->siglock);

                if (why) {
                        read_lock(&tasklist_lock);
                        do_notify_parent_cldstop(current->group_leader, why);
                        read_unlock(&tasklist_lock);
                }
                goto relock;
        }

        for (;;) {
                struct k_sigaction *ka;
                /*
                 * Tracing can induce an artificial signal and choose sigaction.
                 * The return value in @signr determines the default action,
                 * but @info->si_signo is the signal number we will report.
                 */
                signr = tracehook_get_signal(current, regs, info, return_ka);
                if (unlikely(signr < 0))
                        goto relock;
                if (unlikely(signr != 0))
                        ka = return_ka;
                else {
                        if (unlikely(signal->group_stop_count > 0) &&
                            do_signal_stop(0))
                                goto relock;

                        signr = dequeue_signal(current, &current->blocked,
                                               info);

                        if (!signr)
                                break; /* will return 0 */

                        if (signr != SIGKILL) {
                                signr = ptrace_signal(signr, info,
                                                      regs, cookie);
                                if (!signr)
                                        continue;
                        }

                        ka = &sighand->action[signr-1];
                }

                /* Trace actually delivered signals. */
                trace_signal_deliver(signr, info, ka);

                if (ka->sa.sa_handler == SIG_IGN) /* Do nothing.  */
                        continue;
                if (ka->sa.sa_handler != SIG_DFL) {
                        /* Run the handler.  */
                        *return_ka = *ka;

                        if (ka->sa.sa_flags & SA_ONESHOT)
                                ka->sa.sa_handler = SIG_DFL;

                        break; /* will return non-zero "signr" value */
                }

                /*
                 * Now we are doing the default action for this signal.
                 */
                if (sig_kernel_ignore(signr)) /* Default is nothing. */
                        continue;

                /*
                 * Global init gets no signals it doesn't want.
                 * Container-init gets no signals it doesn't want from same
                 * container.
                 *
                 * Note that if global/container-init sees a sig_kernel_only()
                 * signal here, the signal must have been generated internally
                 * or must have come from an ancestor namespace. In either
                 * case, the signal cannot be dropped.
                 */
                if (unlikely(signal->flags & SIGNAL_UNKILLABLE) &&
                                !sig_kernel_only(signr))
                        continue;

                if (sig_kernel_stop(signr)) {
                        /*
                         * The default action is to stop all threads in
                         * the thread group.  The job control signals
                         * do nothing in an orphaned pgrp, but SIGSTOP
                         * always works.  Note that siglock needs to be
                         * dropped during the call to is_orphaned_pgrp()
                         * because of lock ordering with tasklist_lock.
                         * This allows an intervening SIGCONT to be posted.
                         * We need to check for that and bail out if necessary.
                         */
                        if (signr != SIGSTOP) {
                                spin_unlock_irq(&sighand->siglock);

                                /* signals can be posted during this window */

                                if (is_current_pgrp_orphaned())
                                        goto relock;

                                spin_lock_irq(&sighand->siglock);
                        }

                        if (likely(do_signal_stop(info->si_signo))) {
                                /* It released the siglock.  */
                                goto relock;
                        }

                        /*
                         * We didn't actually stop, due to a race
                         * with SIGCONT or something like that.
                         */
                        continue;
                }

                spin_unlock_irq(&sighand->siglock);

                /*
                 * Anything else is fatal, maybe with a core dump.
                 */
                current->flags |= PF_SIGNALED;

                if (sig_kernel_coredump(signr)) {
                        if (print_fatal_signals)
                                print_fatal_signal(regs, info->si_signo);
                        /*
                         * If it was able to dump core, this kills all
                         * other threads in the group and synchronizes with
                         * their demise.  If we lost the race with another
                         * thread getting here, it set group_exit_code
                         * first and our do_group_exit call below will use
                         * that value and ignore the one we pass it.
                         */
                        do_coredump(info->si_signo, info->si_signo, regs);
                }

                /*
                 * Death signals, no core dump.
                 */
                do_group_exit(info->si_signo);
                /* NOTREACHED */
        }
        spin_unlock_irq(&sighand->siglock);
        return signr;
}

void exit_signals(struct task_struct *tsk)
{
        int group_stop = 0;
        struct task_struct *t;

        if (thread_group_empty(tsk) || signal_group_exit(tsk->signal)) {
                tsk->flags |= PF_EXITING;
                return;
        }

        spin_lock_irq(&tsk->sighand->siglock);
        /*
         * From now this task is not visible for group-wide signals,
         * see wants_signal(), do_signal_stop().
         */
        tsk->flags |= PF_EXITING;
        if (!signal_pending(tsk))
                goto out;

        /*
         * It could be that __group_complete_signal() choose us to
         * notify about group-wide signal. Another thread should be
         * woken now to take the signal since we will not.
         */
        for (t = tsk; (t = next_thread(t)) != tsk; )
                if (!signal_pending(t) && !(t->flags & PF_EXITING))
                        recalc_sigpending_and_wake(t);

        if (unlikely(tsk->signal->group_stop_count) &&
                        !--tsk->signal->group_stop_count) {
                tsk->signal->flags = SIGNAL_STOP_STOPPED;
                group_stop = tracehook_notify_jctl(CLD_STOPPED, CLD_STOPPED);
        }
out:
        spin_unlock_irq(&tsk->sighand->siglock);

        if (unlikely(group_stop)) {
                read_lock(&tasklist_lock);
                do_notify_parent_cldstop(tsk, group_stop);
                read_unlock(&tasklist_lock);
        }
}

EXPORT_SYMBOL(recalc_sigpending);
EXPORT_SYMBOL_GPL(dequeue_signal);
EXPORT_SYMBOL(flush_signals);
EXPORT_SYMBOL(force_sig);
EXPORT_SYMBOL(send_sig);
EXPORT_SYMBOL(send_sig_info);
EXPORT_SYMBOL(sigprocmask);
EXPORT_SYMBOL(block_all_signals);
EXPORT_SYMBOL(unblock_all_signals);


/*
 * System call entry points.
 */

/**
 *  sys_restart_syscall - restart a system call
 */
SYSCALL_DEFINE0(restart_syscall)
{
        struct restart_block *restart = &current_thread_info()->restart_block;
        return restart->fn(restart);
}

long do_no_restart_syscall(struct restart_block *param)
{
        return -EINTR;
}

/*
 * We don't need to get the kernel lock - this is all local to this
 * particular thread.. (and that's good, because this is _heavily_
 * used by various programs)
 */

/*
 * This is also useful for kernel threads that want to temporarily
 * (or permanently) block certain signals.
 *
 * NOTE! Unlike the user-mode sys_sigprocmask(), the kernel
 * interface happily blocks "unblockable" signals like SIGKILL
 * and friends.
 */
int sigprocmask(int how, sigset_t *set, sigset_t *oldset)
{
        int error;

        spin_lock_irq(&current->sighand->siglock);
        if (oldset)
                *oldset = current->blocked;

        error = 0;
        switch (how) {
        case SIG_BLOCK:
                sigorsets(&current->blocked, &current->blocked, set);
                break;
        case SIG_UNBLOCK:
                signandsets(&current->blocked, &current->blocked, set);
                break;
        case SIG_SETMASK:
                current->blocked = *set;
                break;
        default:
                error = -EINVAL;
        }
        recalc_sigpending();
        spin_unlock_irq(&current->sighand->siglock);

        return error;
}

/**
 *  sys_rt_sigprocmask - change the list of currently blocked signals
 *  @how: whether to add, remove, or set signals
 *  @set: stores pending signals
 *  @oset: previous value of signal mask if non-null
 *  @sigsetsize: size of sigset_t type
 */
SYSCALL_DEFINE4(rt_sigprocmask, int, how, sigset_t __user *, set,
                sigset_t __user *, oset, size_t, sigsetsize)
{
        int error = -EINVAL;
        sigset_t old_set, new_set;

        /* XXX: Don't preclude handling different sized sigset_t's.  */
        if (sigsetsize != sizeof(sigset_t))
                goto out;

        if (set) {
                error = -EFAULT;
                if (copy_from_user(&new_set, set, sizeof(*set)))
                        goto out;
                sigdelsetmask(&new_set, sigmask(SIGKILL)|sigmask(SIGSTOP));

                error = sigprocmask(how, &new_set, &old_set);
                if (error)
                        goto out;
                if (oset)
                        goto set_old;
        } else if (oset) {
                spin_lock_irq(&current->sighand->siglock);
                old_set = current->blocked;
                spin_unlock_irq(&current->sighand->siglock);

        set_old:
                error = -EFAULT;
                if (copy_to_user(oset, &old_set, sizeof(*oset)))
                        goto out;
        }
        error = 0;
out:
        return error;
}

long do_sigpending(void __user *set, unsigned long sigsetsize)
{
        long error = -EINVAL;
        sigset_t pending;

        if (sigsetsize > sizeof(sigset_t))
                goto out;

        spin_lock_irq(&current->sighand->siglock);
        sigorsets(&pending, &current->pending.signal,
                  &current->signal->shared_pending.signal);
        spin_unlock_irq(&current->sighand->siglock);

        /* Outside the lock because only this thread touches it.  */
        sigandsets(&pending, &current->blocked, &pending);

        error = -EFAULT;
        if (!copy_to_user(set, &pending, sigsetsize))
                error = 0;

out:
        return error;
}

/**
 *  sys_rt_sigpending - examine a pending signal that has been raised
 *                      while blocked
 *  @set: stores pending signals
 *  @sigsetsize: size of sigset_t type or larger
 */
SYSCALL_DEFINE2(rt_sigpending, sigset_t __user *, set, size_t, sigsetsize)
{
        return do_sigpending(set, sigsetsize);
}

#ifndef HAVE_ARCH_COPY_SIGINFO_TO_USER

int copy_siginfo_to_user(siginfo_t __user *to, siginfo_t *from)
{
        int err;

        if (!access_ok (VERIFY_WRITE, to, sizeof(siginfo_t)))
                return -EFAULT;
        if (from->si_code < 0)
                return __copy_to_user(to, from, sizeof(siginfo_t))
                        ? -EFAULT : 0;
        /*
         * If you change siginfo_t structure, please be sure
         * this code is fixed accordingly.
         * Please remember to update the signalfd_copyinfo() function
         * inside fs/signalfd.c too, in case siginfo_t changes.
         * It should never copy any pad contained in the structure
         * to avoid security leaks, but must copy the generic
         * 3 ints plus the relevant union member.
         */
        err = __put_user(from->si_signo, &to->si_signo);
        err |= __put_user(from->si_errno, &to->si_errno);
        err |= __put_user((short)from->si_code, &to->si_code);
        switch (from->si_code & __SI_MASK) {
        case __SI_KILL:
                err |= __put_user(from->si_pid, &to->si_pid);
                err |= __put_user(from->si_uid, &to->si_uid);
                break;
        case __SI_TIMER:
                 err |= __put_user(from->si_tid, &to->si_tid);
                 err |= __put_user(from->si_overrun, &to->si_overrun);
                 err |= __put_user(from->si_ptr, &to->si_ptr);
                break;
        case __SI_POLL:
                err |= __put_user(from->si_band, &to->si_band);
                err |= __put_user(from->si_fd, &to->si_fd);
                break;
        case __SI_FAULT:
                err |= __put_user(from->si_addr, &to->si_addr);
#ifdef __ARCH_SI_TRAPNO
                err |= __put_user(from->si_trapno, &to->si_trapno);
#endif
#ifdef BUS_MCEERR_AO
                /*
                 * Other callers might not initialize the si_lsb field,
                 * so check explicitly for the right codes here.
                 */
                if (from->si_code == BUS_MCEERR_AR || from->si_code == BUS_MCEERR_AO)
                        err |= __put_user(from->si_addr_lsb, &to->si_addr_lsb);
#endif
                break;
        case __SI_CHLD:
                err |= __put_user(from->si_pid, &to->si_pid);
                err |= __put_user(from->si_uid, &to->si_uid);
                err |= __put_user(from->si_status, &to->si_status);
                err |= __put_user(from->si_utime, &to->si_utime);
                err |= __put_user(from->si_stime, &to->si_stime);
                break;
        case __SI_RT: /* This is not generated by the kernel as of now. */
        case __SI_MESGQ: /* But this is */
                err |= __put_user(from->si_pid, &to->si_pid);
                err |= __put_user(from->si_uid, &to->si_uid);
                err |= __put_user(from->si_ptr, &to->si_ptr);
                break;
        default: /* this is just in case for now ... */
                err |= __put_user(from->si_pid, &to->si_pid);
                err |= __put_user(from->si_uid, &to->si_uid);
                break;
        }
        return err;
}

#endif

/**
 *  sys_rt_sigtimedwait - synchronously wait for queued signals specified
 *                      in @uthese
 *  @uthese: queued signals to wait for
 *  @uinfo: if non-null, the signal's siginfo is returned here
 *  @uts: upper bound on process time suspension
 *  @sigsetsize: size of sigset_t type
 */
SYSCALL_DEFINE4(rt_sigtimedwait, const sigset_t __user *, uthese,
                siginfo_t __user *, uinfo, const struct timespec __user *, uts,
                size_t, sigsetsize)
{
        int ret, sig;
        sigset_t these;
        struct timespec ts;
        siginfo_t info;
        long timeout = 0;

        /* XXX: Don't preclude handling different sized sigset_t's.  */
        if (sigsetsize != sizeof(sigset_t))
                return -EINVAL;

        if (copy_from_user(&these, uthese, sizeof(these)))
                return -EFAULT;

        /*
         * Invert the set of allowed signals to get those we
         * want to block.
         */
        sigdelsetmask(&these, sigmask(SIGKILL)|sigmask(SIGSTOP));
        signotset(&these);

        if (uts) {
                if (copy_from_user(&ts, uts, sizeof(ts)))
                        return -EFAULT;
                if (ts.tv_nsec >= 1000000000L || ts.tv_nsec < 0
                    || ts.tv_sec < 0)
                        return -EINVAL;
        }

        spin_lock_irq(&current->sighand->siglock);
        sig = dequeue_signal(current, &these, &info);
        if (!sig) {
                timeout = MAX_SCHEDULE_TIMEOUT;
                if (uts)
                        timeout = (timespec_to_jiffies(&ts)
                                   + (ts.tv_sec || ts.tv_nsec));

                if (timeout) {
                        /*
                         * None ready -- temporarily unblock those we're
                         * interested while we are sleeping in so that we'll
                         * be awakened when they arrive.
                         */
                        current->real_blocked = current->blocked;
                        sigandsets(&current->blocked, &current->blocked, &these);
                        recalc_sigpending();
                        spin_unlock_irq(&current->sighand->siglock);

                        timeout = schedule_timeout_interruptible(timeout);

                        spin_lock_irq(&current->sighand->siglock);
                        sig = dequeue_signal(current, &these, &info);
                        current->blocked = current->real_blocked;
                        siginitset(&current->real_blocked, 0);
                        recalc_sigpending();
                }
        }
        spin_unlock_irq(&current->sighand->siglock);

        if (sig) {
                ret = sig;
                if (uinfo) {
                        if (copy_siginfo_to_user(uinfo, &info))
                                ret = -EFAULT;
                }
        } else {
                ret = -EAGAIN;
                if (timeout)
                        ret = -EINTR;
        }

        return ret;
}

/**
 *  sys_kill - send a signal to a process
 *  @pid: the PID of the process
 *  @sig: signal to be sent
 */
SYSCALL_DEFINE2(kill, pid_t, pid, int, sig)
{
        struct siginfo info;

        info.si_signo = sig;
        info.si_errno = 0;
        info.si_code = SI_USER;
        info.si_pid = task_tgid_vnr(current);
        info.si_uid = current_uid();

        return kill_something_info(sig, &info, pid);
}

static int
do_send_specific(pid_t tgid, pid_t pid, int sig, struct siginfo *info)
{
        struct task_struct *p;
        int error = -ESRCH;

        rcu_read_lock();
        p = find_task_by_vpid(pid);
        if (p && (tgid <= 0 || task_tgid_vnr(p) == tgid)) {
                error = check_kill_permission(sig, info, p);
                /*
                 * The null signal is a permissions and process existence
                 * probe.  No signal is actually delivered.
                 */
                if (!error && sig) {
                        error = do_send_sig_info(sig, info, p, false);
                        /*
                         * If lock_task_sighand() failed we pretend the task
                         * dies after receiving the signal. The window is tiny,
                         * and the signal is private anyway.
                         */
                        if (unlikely(error == -ESRCH))
                                error = 0;
                }
        }
        rcu_read_unlock();

        return error;
}

static int do_tkill(pid_t tgid, pid_t pid, int sig)
{
        struct siginfo info;

        info.si_signo = sig;
        info.si_errno = 0;
        info.si_code = SI_TKILL;
        info.si_pid = task_tgid_vnr(current);
        info.si_uid = current_uid();

        return do_send_specific(tgid, pid, sig, &info);
}

/**
 *  sys_tgkill - send signal to one specific thread
 *  @tgid: the thread group ID of the thread
 *  @pid: the PID of the thread
 *  @sig: signal to be sent
 *
 *  This syscall also checks the @tgid and returns -ESRCH even if the PID
 *  exists but it's not belonging to the target process anymore. This
 *  method solves the problem of threads exiting and PIDs getting reused.
 */
SYSCALL_DEFINE3(tgkill, pid_t, tgid, pid_t, pid, int, sig)
{
        /* This is only valid for single tasks */
        if (pid <= 0 || tgid <= 0)
                return -EINVAL;

        return do_tkill(tgid, pid, sig);
}

/**
 *  sys_tkill - send signal to one specific task
 *  @pid: the PID of the task
 *  @sig: signal to be sent
 *
 *  Send a signal to only one task, even if it's a CLONE_THREAD task.
 */
SYSCALL_DEFINE2(tkill, pid_t, pid, int, sig)
{
        /* This is only valid for single tasks */
        if (pid <= 0)
                return -EINVAL;

        return do_tkill(0, pid, sig);
}

/**
 *  sys_rt_sigqueueinfo - send signal information to a signal
 *  @pid: the PID of the thread
 *  @sig: signal to be sent
 *  @uinfo: signal info to be sent
 */
SYSCALL_DEFINE3(rt_sigqueueinfo, pid_t, pid, int, sig,
                siginfo_t __user *, uinfo)
{
        siginfo_t info;

        if (copy_from_user(&info, uinfo, sizeof(siginfo_t)))
                return -EFAULT;

        /* Not even root can pretend to send signals from the kernel.
         * Nor can they impersonate a kill()/tgkill(), which adds source info.
         */
        if (info.si_code >= 0 || info.si_code == SI_TKILL) {
                /* We used to allow any < 0 si_code */
                WARN_ON_ONCE(info.si_code < 0);
                return -EPERM;
        }
        info.si_signo = sig;

        /* POSIX.1b doesn't mention process groups.  */
        return kill_proc_info(sig, &info, pid);
}

long do_rt_tgsigqueueinfo(pid_t tgid, pid_t pid, int sig, siginfo_t *info)
{
        /* This is only valid for single tasks */
        if (pid <= 0 || tgid <= 0)
                return -EINVAL;

        /* Not even root can pretend to send signals from the kernel.
         * Nor can they impersonate a kill()/tgkill(), which adds source info.
         */
        if (info->si_code >= 0 || info->si_code == SI_TKILL) {
                /* We used to allow any < 0 si_code */
                WARN_ON_ONCE(info->si_code < 0);
                return -EPERM;
        }
        info->si_signo = sig;

        return do_send_specific(tgid, pid, sig, info);
}

SYSCALL_DEFINE4(rt_tgsigqueueinfo, pid_t, tgid, pid_t, pid, int, sig,
                siginfo_t __user *, uinfo)
{
        siginfo_t info;

        if (copy_from_user(&info, uinfo, sizeof(siginfo_t)))
                return -EFAULT;

        return do_rt_tgsigqueueinfo(tgid, pid, sig, &info);
}

int do_sigaction(int sig, struct k_sigaction *act, struct k_sigaction *oact)
{
        struct task_struct *t = current;
        struct k_sigaction *k;
        sigset_t mask;

        if (!valid_signal(sig) || sig < 1 || (act && sig_kernel_only(sig)))
                return -EINVAL;

        k = &t->sighand->action[sig-1];

        spin_lock_irq(&current->sighand->siglock);
        if (oact)
                *oact = *k;

        if (act) {
                sigdelsetmask(&act->sa.sa_mask,
                              sigmask(SIGKILL) | sigmask(SIGSTOP));
                *k = *act;
                /*
                 * POSIX 3.3.1.3:
                 *  "Setting a signal action to SIG_IGN for a signal that is
                 *   pending shall cause the pending signal to be discarded,
                 *   whether or not it is blocked."
                 *
                 *  "Setting a signal action to SIG_DFL for a signal that is
                 *   pending and whose default action is to ignore the signal
                 *   (for example, SIGCHLD), shall cause the pending signal to
                 *   be discarded, whether or not it is blocked"
                 */
                if (sig_handler_ignored(sig_handler(t, sig), sig)) {
                        sigemptyset(&mask);
                        sigaddset(&mask, sig);
                        rm_from_queue_full(&mask, &t->signal->shared_pending);
                        do {
                                rm_from_queue_full(&mask, &t->pending);
                                t = next_thread(t);
                        } while (t != current);
                }
        }

        spin_unlock_irq(&current->sighand->siglock);
        return 0;
}

int 
do_sigaltstack (const stack_t __user *uss, stack_t __user *uoss, unsigned long sp)
{
        stack_t oss;
        int error;

        oss.ss_sp = (void __user *) current->sas_ss_sp;
        oss.ss_size = current->sas_ss_size;
        oss.ss_flags = sas_ss_flags(sp);

        if (uss) {
                void __user *ss_sp;
                size_t ss_size;
                int ss_flags;

                error = -EFAULT;
                if (!access_ok(VERIFY_READ, uss, sizeof(*uss)))
                        goto out;
                error = __get_user(ss_sp, &uss->ss_sp) |
                        __get_user(ss_flags, &uss->ss_flags) |
                        __get_user(ss_size, &uss->ss_size);
                if (error)
                        goto out;

                error = -EPERM;
                if (on_sig_stack(sp))
                        goto out;

                error = -EINVAL;
                /*
                 * Note - this code used to test ss_flags incorrectly:
                 *        old code may have been written using ss_flags==0
                 *        to mean ss_flags==SS_ONSTACK (as this was the only
                 *        way that worked) - this fix preserves that older
                 *        mechanism.
                 */
                if (ss_flags != SS_DISABLE && ss_flags != SS_ONSTACK && ss_flags != 0)
                        goto out;

                if (ss_flags == SS_DISABLE) {
                        ss_size = 0;
                        ss_sp = NULL;
                } else {
                        error = -ENOMEM;
                        if (ss_size < MINSIGSTKSZ)
                                goto out;
                }

                current->sas_ss_sp = (unsigned long) ss_sp;
                current->sas_ss_size = ss_size;
        }

        error = 0;
        if (uoss) {
                error = -EFAULT;
                if (!access_ok(VERIFY_WRITE, uoss, sizeof(*uoss)))
                        goto out;
                error = __put_user(oss.ss_sp, &uoss->ss_sp) |
                        __put_user(oss.ss_size, &uoss->ss_size) |
                        __put_user(oss.ss_flags, &uoss->ss_flags);
        }

out:
        return error;
}

#ifdef __ARCH_WANT_SYS_SIGPENDING

/**
 *  sys_sigpending - examine pending signals
 *  @set: where mask of pending signal is returned
 */
SYSCALL_DEFINE1(sigpending, old_sigset_t __user *, set)
{
        return do_sigpending(set, sizeof(*set));
}

#endif

#ifdef __ARCH_WANT_SYS_SIGPROCMASK
/**
 *  sys_sigprocmask - examine and change blocked signals
 *  @how: whether to add, remove, or set signals
 *  @set: signals to add or remove (if non-null)
 *  @oset: previous value of signal mask if non-null
 *
 * Some platforms have their own version with special arguments;
 * others support only sys_rt_sigprocmask.
 */

SYSCALL_DEFINE3(sigprocmask, int, how, old_sigset_t __user *, set,
                old_sigset_t __user *, oset)
{
        int error;
        old_sigset_t old_set, new_set;

        if (set) {
                error = -EFAULT;
                if (copy_from_user(&new_set, set, sizeof(*set)))
                        goto out;
                new_set &= ~(sigmask(SIGKILL) | sigmask(SIGSTOP));

                spin_lock_irq(&current->sighand->siglock);
                old_set = current->blocked.sig[0];

                error = 0;
                switch (how) {
                default:
                        error = -EINVAL;
                        break;
                case SIG_BLOCK:
                        sigaddsetmask(&current->blocked, new_set);
                        break;
                case SIG_UNBLOCK:
                        sigdelsetmask(&current->blocked, new_set);
                        break;
                case SIG_SETMASK:
                        current->blocked.sig[0] = new_set;
                        break;
                }

                recalc_sigpending();
                spin_unlock_irq(&current->sighand->siglock);
                if (error)
                        goto out;
                if (oset)
                        goto set_old;
        } else if (oset) {
                old_set = current->blocked.sig[0];
        set_old:
                error = -EFAULT;
                if (copy_to_user(oset, &old_set, sizeof(*oset)))
                        goto out;
        }
        error = 0;
out:
        return error;
}
#endif /* __ARCH_WANT_SYS_SIGPROCMASK */

#ifdef __ARCH_WANT_SYS_RT_SIGACTION
/**
 *  sys_rt_sigaction - alter an action taken by a process
 *  @sig: signal to be sent
 *  @act: new sigaction
 *  @oact: used to save the previous sigaction
 *  @sigsetsize: size of sigset_t type
 */
SYSCALL_DEFINE4(rt_sigaction, int, sig,
                const struct sigaction __user *, act,
                struct sigaction __user *, oact,
                size_t, sigsetsize)
{
        struct k_sigaction new_sa, old_sa;
        int ret = -EINVAL;

        /* XXX: Don't preclude handling different sized sigset_t's.  */
        if (sigsetsize != sizeof(sigset_t))
                goto out;

        if (act) {
                if (copy_from_user(&new_sa.sa, act, sizeof(new_sa.sa)))
                        return -EFAULT;
        }

        ret = do_sigaction(sig, act ? &new_sa : NULL, oact ? &old_sa : NULL);

        if (!ret && oact) {
                if (copy_to_user(oact, &old_sa.sa, sizeof(old_sa.sa)))
                        return -EFAULT;
        }
out:
        return ret;
}
#endif /* __ARCH_WANT_SYS_RT_SIGACTION */

#ifdef __ARCH_WANT_SYS_SGETMASK

/*
 * For backwards compatibility.  Functionality superseded by sigprocmask.
 */
SYSCALL_DEFINE0(sgetmask)
{
        /* SMP safe */
        return current->blocked.sig[0];
}

SYSCALL_DEFINE1(ssetmask, int, newmask)
{
        int old;

        spin_lock_irq(&current->sighand->siglock);
        old = current->blocked.sig[0];

        siginitset(&current->blocked, newmask & ~(sigmask(SIGKILL)|
                                                  sigmask(SIGSTOP)));
        recalc_sigpending();
        spin_unlock_irq(&current->sighand->siglock);

        return old;
}
#endif /* __ARCH_WANT_SGETMASK */

#ifdef __ARCH_WANT_SYS_SIGNAL
/*
 * For backwards compatibility.  Functionality superseded by sigaction.
 */
SYSCALL_DEFINE2(signal, int, sig, __sighandler_t, handler)
{
        struct k_sigaction new_sa, old_sa;
        int ret;

        new_sa.sa.sa_handler = handler;
        new_sa.sa.sa_flags = SA_ONESHOT | SA_NOMASK;
        sigemptyset(&new_sa.sa.sa_mask);

        ret = do_sigaction(sig, &new_sa, &old_sa);

        return ret ? ret : (unsigned long)old_sa.sa.sa_handler;
}
#endif /* __ARCH_WANT_SYS_SIGNAL */

#ifdef __ARCH_WANT_SYS_PAUSE

SYSCALL_DEFINE0(pause)
{
        current->state = TASK_INTERRUPTIBLE;
        schedule();
        return -ERESTARTNOHAND;
}

#endif

#ifdef __ARCH_WANT_SYS_RT_SIGSUSPEND
/**
 *  sys_rt_sigsuspend - replace the signal mask for a value with the
 *      @unewset value until a signal is received
 *  @unewset: new signal mask value
 *  @sigsetsize: size of sigset_t type
 */
SYSCALL_DEFINE2(rt_sigsuspend, sigset_t __user *, unewset, size_t, sigsetsize)
{
        sigset_t newset;

        /* XXX: Don't preclude handling different sized sigset_t's.  */
        if (sigsetsize != sizeof(sigset_t))
                return -EINVAL;

        if (copy_from_user(&newset, unewset, sizeof(newset)))
                return -EFAULT;
        sigdelsetmask(&newset, sigmask(SIGKILL)|sigmask(SIGSTOP));

        spin_lock_irq(&current->sighand->siglock);
        current->saved_sigmask = current->blocked;
        current->blocked = newset;
        recalc_sigpending();
        spin_unlock_irq(&current->sighand->siglock);

        current->state = TASK_INTERRUPTIBLE;
        schedule();
        set_restore_sigmask();
        return -ERESTARTNOHAND;
}
#endif /* __ARCH_WANT_SYS_RT_SIGSUSPEND */

__attribute__((weak)) const char *arch_vma_name(struct vm_area_struct *vma)
{
        return NULL;
}

void __init signals_init(void)
{
        sigqueue_cachep = KMEM_CACHE(sigqueue, SLAB_PANIC);
}

#ifdef CONFIG_KGDB_KDB
#include <linux/kdb.h>
/*
 * kdb_send_sig_info - Allows kdb to send signals without exposing
 * signal internals.  This function checks if the required locks are
 * available before calling the main signal code, to avoid kdb
 * deadlocks.
 */
void
kdb_send_sig_info(struct task_struct *t, struct siginfo *info)
{
        static struct task_struct *kdb_prev_t;
        int sig, new_t;
        if (!spin_trylock(&t->sighand->siglock)) {
                kdb_printf("Can't do kill command now.\n"
                           "The sigmask lock is held somewhere else in "
                           "kernel, try again later\n");
                return;
        }
        spin_unlock(&t->sighand->siglock);
        new_t = kdb_prev_t != t;
        kdb_prev_t = t;
        if (t->state != TASK_RUNNING && new_t) {
                kdb_printf("Process is not RUNNING, sending a signal from "
                           "kdb risks deadlock\n"
                           "on the run queue locks. "
                           "The signal has _not_ been sent.\n"
                           "Reissue the kill command if you want to risk "
                           "the deadlock.\n");
                return;
        }
        sig = info->si_signo;
        if (send_sig_info(sig, info, t))
                kdb_printf("Fail to deliver Signal %d to process %d.\n",
                           sig, t->pid);
        else
                kdb_printf("Signal %d is sent to process %d.\n", sig, t->pid);
}
#endif  /* CONFIG_KGDB_KDB */