FreeBSD/Linux Kernel Cross Reference
sys/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/export.h>
    #include <linux/init.h>
    #include <linux/sched.h>
    #include <linux/fs.h>
    #include <linux/tty.h>
    #include <linux/binfmts.h>
    #include <linux/coredump.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>
    #include <linux/user_namespace.h>
    #include <linux/uprobes.h>
    #include <linux/compat.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 <asm/cacheflush.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, bool force)
    {
            void __user *handler;
    
            handler = sig_handler(t, sig);
    
            if (unlikely(t->signal->flags & SIGNAL_UNKILLABLE) &&
                            handler == SIG_DFL && !force)
                    return 1;
    
            return sig_handler_ignored(handler, sig);
    }
    
    static int sig_ignored(struct task_struct *t, int sig, bool force)
    {
            /*
             * 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, force))
                    return 0;
    
            /*
             * Tracers may want to know about even ignored signals.
             */
            return !t->ptrace;
    }
    
    /*
     * 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->jobctl & JOBCTL_PENDING_MASK) ||
               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 (!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) | sigmask(SIGSYS))
   
   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);
   }
   
   /**
    * task_set_jobctl_pending - set jobctl pending bits
    * @task: target task
    * @mask: pending bits to set
    *
    * Clear @mask from @task->jobctl.  @mask must be subset of
    * %JOBCTL_PENDING_MASK | %JOBCTL_STOP_CONSUME | %JOBCTL_STOP_SIGMASK |
    * %JOBCTL_TRAPPING.  If stop signo is being set, the existing signo is
    * cleared.  If @task is already being killed or exiting, this function
    * becomes noop.
    *
    * CONTEXT:
    * Must be called with @task->sighand->siglock held.
    *
    * RETURNS:
    * %true if @mask is set, %false if made noop because @task was dying.
    */
   bool task_set_jobctl_pending(struct task_struct *task, unsigned int mask)
   {
           BUG_ON(mask & ~(JOBCTL_PENDING_MASK | JOBCTL_STOP_CONSUME |
                           JOBCTL_STOP_SIGMASK | JOBCTL_TRAPPING));
           BUG_ON((mask & JOBCTL_TRAPPING) && !(mask & JOBCTL_PENDING_MASK));
   
           if (unlikely(fatal_signal_pending(task) || (task->flags & PF_EXITING)))
                   return false;
   
           if (mask & JOBCTL_STOP_SIGMASK)
                   task->jobctl &= ~JOBCTL_STOP_SIGMASK;
   
           task->jobctl |= mask;
           return true;
   }
   
   /**
    * task_clear_jobctl_trapping - clear jobctl trapping bit
    * @task: target task
    *
    * If JOBCTL_TRAPPING is set, a ptracer is waiting for us to enter TRACED.
    * Clear it and wake up the ptracer.  Note that we don't need any further
    * locking.  @task->siglock guarantees that @task->parent points to the
    * ptracer.
    *
    * CONTEXT:
    * Must be called with @task->sighand->siglock held.
    */
   void task_clear_jobctl_trapping(struct task_struct *task)
   {
           if (unlikely(task->jobctl & JOBCTL_TRAPPING)) {
                   task->jobctl &= ~JOBCTL_TRAPPING;
                   wake_up_bit(&task->jobctl, JOBCTL_TRAPPING_BIT);
           }
   }
   
   /**
    * task_clear_jobctl_pending - clear jobctl pending bits
    * @task: target task
    * @mask: pending bits to clear
    *
    * Clear @mask from @task->jobctl.  @mask must be subset of
    * %JOBCTL_PENDING_MASK.  If %JOBCTL_STOP_PENDING is being cleared, other
    * STOP bits are cleared together.
    *
    * If clearing of @mask leaves no stop or trap pending, this function calls
    * task_clear_jobctl_trapping().
    *
    * CONTEXT:
    * Must be called with @task->sighand->siglock held.
    */
   void task_clear_jobctl_pending(struct task_struct *task, unsigned int mask)
   {
           BUG_ON(mask & ~JOBCTL_PENDING_MASK);
   
           if (mask & JOBCTL_STOP_PENDING)
                   mask |= JOBCTL_STOP_CONSUME | JOBCTL_STOP_DEQUEUED;
   
           task->jobctl &= ~mask;
   
           if (!(task->jobctl & JOBCTL_PENDING_MASK))
                   task_clear_jobctl_trapping(task);
   }
   
   /**
    * task_participate_group_stop - participate in a group stop
    * @task: task participating in a group stop
    *
    * @task has %JOBCTL_STOP_PENDING set and is participating in a group stop.
    * Group stop states are cleared and the group stop count is consumed if
    * %JOBCTL_STOP_CONSUME was set.  If the consumption completes the group
    * stop, the appropriate %SIGNAL_* flags are set.
    *
    * CONTEXT:
    * Must be called with @task->sighand->siglock held.
    *
    * RETURNS:
    * %true if group stop completion should be notified to the parent, %false
    * otherwise.
    */
   static bool task_participate_group_stop(struct task_struct *task)
   {
           struct signal_struct *sig = task->signal;
           bool consume = task->jobctl & JOBCTL_STOP_CONSUME;
   
           WARN_ON_ONCE(!(task->jobctl & JOBCTL_STOP_PENDING));
   
           task_clear_jobctl_pending(task, JOBCTL_STOP_PENDING);
   
           if (!consume)
                   return false;
   
           if (!WARN_ON_ONCE(sig->group_stop_count == 0))
                   sig->group_stop_count--;
   
           /*
            * Tell the caller to notify completion iff we are entering into a
            * fresh group stop.  Read comment in do_signal_stop() for details.
            */
           if (!sig->group_stop_count && !(sig->flags & SIGNAL_STOP_STOPPED)) {
                   sig->flags = SIGNAL_STOP_STOPPED;
                   return true;
           }
           return false;
   }
   
   /*
    * 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;
           /* if ptraced, let the tracer determine */
           return !tsk->ptrace;
   }
   
   /*
    * 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.
                    */
                   current->jobctl |= JOBCTL_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_state(struct task_struct *t, unsigned int state)
   {
           set_tsk_thread_flag(t, TIF_SIGPENDING);
           /*
            * TASK_WAKEKILL also means 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.
            */
           if (!wake_up_state(t, state | TASK_INTERRUPTIBLE))
                   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;
   
           sigandnsets(&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 (uid_eq(cred->euid, tcred->suid) ||
               uid_eq(cred->euid, tcred->uid)  ||
               uid_eq(cred->uid,  tcred->suid) ||
               uid_eq(cred->uid,  tcred->uid))
                   return 1;
   
           if (ns_capable(tcred->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);
   }
   
   /**
    * ptrace_trap_notify - schedule trap to notify ptracer
    * @t: tracee wanting to notify tracer
    *
    * This function schedules sticky ptrace trap which is cleared on the next
    * TRAP_STOP to notify ptracer of an event.  @t must have been seized by
    * ptracer.
    *
    * If @t is running, STOP trap will be taken.  If trapped for STOP and
    * ptracer is listening for events, tracee is woken up so that it can
    * re-trap for the new event.  If trapped otherwise, STOP trap will be
    * eventually taken without returning to userland after the existing traps
    * are finished by PTRACE_CONT.
    *
    * CONTEXT:
    * Must be called with @task->sighand->siglock held.
    */
   static void ptrace_trap_notify(struct task_struct *t)
   {
           WARN_ON_ONCE(!(t->ptrace & PT_SEIZED));
           assert_spin_locked(&t->sighand->siglock);
   
           task_set_jobctl_pending(t, JOBCTL_TRAP_NOTIFY);
           ptrace_signal_wake_up(t, t->jobctl & JOBCTL_LISTENING);
   }
   
   /*
    * 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, bool force)
   {
           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, wake all threads.
                    */
                   rm_from_queue(SIG_KERNEL_STOP_MASK, &signal->shared_pending);
                   t = p;
                   do {
                           task_clear_jobctl_pending(t, JOBCTL_STOP_PENDING);
                           rm_from_queue(SIG_KERNEL_STOP_MASK, &t->pending);
                           if (likely(!(t->ptrace & PT_SEIZED)))
                                   wake_up_state(t, __TASK_STOPPED);
                           else
                                   ptrace_trap_notify(t);
                   } 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;
                   }
           }
   
           return !sig_ignored(p, sig, force);
   }
   
   /*
    * 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 || !t->ptrace)) {
                   /*
                    * 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 {
                                   task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
                                   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);
  }
  
  #ifdef CONFIG_USER_NS
  static inline void userns_fixup_signal_uid(struct siginfo *info, struct task_struct *t)
  {
          if (current_user_ns() == task_cred_xxx(t, user_ns))
                  return;
  
          if (SI_FROMKERNEL(info))
                  return;
  
          rcu_read_lock();
          info->si_uid = from_kuid_munged(task_cred_xxx(t, user_ns),
                                          make_kuid(current_user_ns(), info->si_uid));
          rcu_read_unlock();
  }
  #else
  static inline void userns_fixup_signal_uid(struct siginfo *info, struct task_struct *t)
  {
          return;
  }
  #endif
  
  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;
          int ret = 0, result;
  
          assert_spin_locked(&t->sighand->siglock);
  
          result = TRACE_SIGNAL_IGNORED;
          if (!prepare_signal(sig, t,
                          from_ancestor_ns || (info == SEND_SIG_FORCED)))
                  goto ret;
  
          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.
           */
          result = TRACE_SIGNAL_ALREADY_PENDING;
          if (legacy_queue(pending, sig))
                  goto ret;
  
          result = TRACE_SIGNAL_DELIVERED;
          /*
           * 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 = from_kuid_munged(current_user_ns(), 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;
                  }
  
                  userns_fixup_signal_uid(&q->info, t);
  
          } 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().
                           */
                          result = TRACE_SIGNAL_OVERFLOW_FAIL;
                          ret = -EAGAIN;
                          goto ret;
                  } else {
                          /*
                           * This is a silent loss of information.  We still
                           * send the signal, but the *info bits are lost.
                           */
                          result = TRACE_SIGNAL_LOSE_INFO;
                  }
          }
  
  out_set:
          signalfd_notify(t, sig);
          sigaddset(&pending->signal, sig);
          complete_signal(sig, t, group);
  ret:
          trace_signal_generate(sig, info, t, group, result);
          return ret;
  }
  
  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(int signr)
  {
          struct pt_regs *regs = signal_pt_regs();
          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) {
                  task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
                  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;
  
          for (;;) {
                  local_irq_save(*flags);
                  rcu_read_lock();
                  sighand = rcu_dereference(tsk->sighand);
                  if (unlikely(sighand == NULL)) {
                          rcu_read_unlock();
                          local_irq_restore(*flags);
                          break;
                  }
  
                  spin_lock(&sighand->siglock);
                  if (likely(sighand == tsk->sighand)) {
                          rcu_read_unlock();
                          break;
                  }
                  spin_unlock(&sighand->siglock);
                  rcu_read_unlock();
                  local_irq_restore(*flags);
          }
  
          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;
  }
  
  static int kill_as_cred_perm(const struct cred *cred,
                               struct task_struct *target)
  {
          const struct cred *pcred = __task_cred(target);
          if (!uid_eq(cred->euid, pcred->suid) && !uid_eq(cred->euid, pcred->uid) &&
              !uid_eq(cred->uid,  pcred->suid) && !uid_eq(cred->uid,  pcred->uid))
                  return 0;
          return 1;
  }
  
  /* like kill_pid_info(), but doesn't use uid/euid of "current" */
  int kill_pid_info_as_cred(int sig, struct siginfo *info, struct pid *pid,
                           const struct cred *cred, u32 secid)
  {
          int ret = -EINVAL;
          struct task_struct *p;
          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;
          }
          if (si_fromuser(info) && !kill_as_cred_perm(cred, p)) {
                  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_cred);
  
  /*
   * 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, result;
  
          BUG_ON(!(q->flags & SIGQUEUE_PREALLOC));
  
          ret = -1;
          if (!likely(lock_task_sighand(t, &flags)))
                  goto ret;
  
          ret = 1; /* the signal is ignored */
          result = TRACE_SIGNAL_IGNORED;
          if (!prepare_signal(sig, t, false))
                  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++;
                  result = TRACE_SIGNAL_ALREADY_PENDING;
                  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);
          result = TRACE_SIGNAL_DELIVERED;
  out:
          trace_signal_generate(sig, &q->info, t, group, result);
          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 true if our parent ignored us and so we've switched to
   * self-reaping.
   */
  bool do_notify_parent(struct task_struct *tsk, int sig)
  {
          struct siginfo info;
          unsigned long flags;
          struct sighand_struct *psig;
          bool autoreap = false;
  
          BUG_ON(sig == -1);
  
          /* do_notify_parent_cldstop should have been called instead.  */
          BUG_ON(task_is_stopped_or_traced(tsk));
  
          BUG_ON(!tsk->ptrace &&
                 (tsk->group_leader != tsk || !thread_group_empty(tsk)));
  
          if (sig != SIGCHLD) {
                  /*
                   * This is only possible if parent == real_parent.
                   * Check if it has changed security domain.
                   */
                  if (tsk->parent_exec_id != tsk->parent->self_exec_id)
                          sig = SIGCHLD;
          }
  
          info.si_signo = sig;
          info.si_errno = 0;
          /*
           * We are under tasklist_lock here so our parent is tied to
           * us and cannot change.
           *
           * task_active_pid_ns will always return the same pid namespace
           * until a task passes through release_task.
           *
           * 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, task_active_pid_ns(tsk->parent));
          info.si_uid = from_kuid_munged(task_cred_xxx(tsk->parent, user_ns),
                                         task_uid(tsk));
          rcu_read_unlock();
  
          info.si_utime = cputime_to_clock_t(tsk->utime + tsk->signal->utime);
          info.si_stime = cputime_to_clock_t(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 (!tsk->ptrace && 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).
                   */
                  autoreap = true;
                  if (psig->action[SIGCHLD-1].sa.sa_handler == SIG_IGN)
                          sig = 0;
          }
          if (valid_signal(sig) && sig)
                  __group_send_sig_info(sig, &info, tsk->parent);
          __wake_up_parent(tsk, tsk->parent);
          spin_unlock_irqrestore(&psig->siglock, flags);
  
          return autoreap;
  }
  
  /**
   * do_notify_parent_cldstop - notify parent of stopped/continued state change
   * @tsk: task reporting the state change
   * @for_ptracer: the notification is for ptracer
   * @why: CLD_{CONTINUED|STOPPED|TRAPPED} to report
   *
   * Notify @tsk's parent that the stopped/continued state has changed.  If
   * @for_ptracer is %false, @tsk's group leader notifies to its real parent.
   * If %true, @tsk reports to @tsk->parent which should be the ptracer.
   *
   * CONTEXT:
   * Must be called with tasklist_lock at least read locked.
   */
  static void do_notify_parent_cldstop(struct task_struct *tsk,
                                       bool for_ptracer, int why)
  {
          struct siginfo info;
          unsigned long flags;
          struct task_struct *parent;
          struct sighand_struct *sighand;
  
          if (for_ptracer) {
                  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, task_active_pid_ns(parent));
          info.si_uid = from_kuid_munged(task_cred_xxx(parent, user_ns), task_uid(tsk));
          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(current->ptrace))
                  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().
           *
           * This is almost outdated, a task with the pending SIGKILL can't
           * block in TASK_TRACED. But PTRACE_EVENT_EXIT can be reported
           * after SIGKILL was already dequeued.
           */
          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 why, int clear_code, siginfo_t *info)
          __releases(&current->sighand->siglock)
          __acquires(&current->sighand->siglock)
  {
          bool gstop_done = false;
  
          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;
          }
  
          /*
           * We're committing to trapping.  TRACED should be visible before
           * TRAPPING is cleared; otherwise, the tracer might fail do_wait().
           * Also, transition to TRACED and updates to ->jobctl should be
           * atomic with respect to siglock and should be done after the arch
           * hook as siglock is released and regrabbed across it.
           */
          set_current_state(TASK_TRACED);
  
          current->last_siginfo = info;
          current->exit_code = exit_code;
  
          /*
           * If @why is CLD_STOPPED, we're trapping to participate in a group
           * stop.  Do the bookkeeping.  Note that if SIGCONT was delievered
           * across siglock relocks since INTERRUPT was scheduled, PENDING
           * could be clear now.  We act as if SIGCONT is received after
           * TASK_TRACED is entered - ignore it.
           */
          if (why == CLD_STOPPED && (current->jobctl & JOBCTL_STOP_PENDING))
                  gstop_done = task_participate_group_stop(current);
  
          /* any trap clears pending STOP trap, STOP trap clears NOTIFY */
          task_clear_jobctl_pending(current, JOBCTL_TRAP_STOP);
          if (info && info->si_code >> 8 == PTRACE_EVENT_STOP)
                  task_clear_jobctl_pending(current, JOBCTL_TRAP_NOTIFY);
  
          /* entering a trap, clear TRAPPING */
          task_clear_jobctl_trapping(current);
  
          spin_unlock_irq(&current->sighand->siglock);
          read_lock(&tasklist_lock);
          if (may_ptrace_stop()) {
                  /*
                   * Notify parents of the stop.
                   *
                   * While ptraced, there are two parents - the ptracer and
                   * the real_parent of the group_leader.  The ptracer should
                   * know about every stop while the real parent is only
                   * interested in the completion of group stop.  The states
                   * for the two don't interact with each other.  Notify
                   * separately unless they're gonna be duplicates.
                   */
                  do_notify_parent_cldstop(current, true, why);
                  if (gstop_done && ptrace_reparented(current))
                          do_notify_parent_cldstop(current, false, why);
  
                  /*
                   * 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();
                  freezable_schedule();
          } else {
                  /*
                   * By the time we got the lock, our tracer went away.
                   * Don't drop the lock yet, another tracer may come.
                   *
                   * If @gstop_done, the ptracer went away between group stop
                   * completion and here.  During detach, it would have set
                   * JOBCTL_STOP_PENDING on us and we'll re-enter
                   * TASK_STOPPED in do_signal_stop() on return, so notifying
                   * the real parent of the group stop completion is enough.
                   */
                  if (gstop_done)
                          do_notify_parent_cldstop(current, false, why);
  
                  /* tasklist protects us from ptrace_freeze_traced() */
                  __set_current_state(TASK_RUNNING);
                  if (clear_code)
                          current->exit_code = 0;
                  read_unlock(&tasklist_lock);
          }
  
          /*
           * 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;
  
          /* LISTENING can be set only during STOP traps, clear it */
          current->jobctl &= ~JOBCTL_LISTENING;
  
          /*
           * 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);
  }
  
  static void ptrace_do_notify(int signr, int exit_code, int why)
  {
          siginfo_t info;
  
          memset(&info, 0, sizeof info);
          info.si_signo = signr;
          info.si_code = exit_code;
          info.si_pid = task_pid_vnr(current);
          info.si_uid = from_kuid_munged(current_user_ns(), current_uid());
  
          /* Let the debugger run.  */
          ptrace_stop(exit_code, why, 1, &info);
  }
  
  void ptrace_notify(int exit_code)
  {
          BUG_ON((exit_code & (0x7f | ~0xffff)) != SIGTRAP);
          if (unlikely(current->task_works))
                  task_work_run();
  
          spin_lock_irq(&current->sighand->siglock);
          ptrace_do_notify(SIGTRAP, exit_code, CLD_TRAPPED);
          spin_unlock_irq(&current->sighand->siglock);
  }
  
  /**
   * do_signal_stop - handle group stop for SIGSTOP and other stop signals
   * @signr: signr causing group stop if initiating
   *
   * If %JOBCTL_STOP_PENDING is not set yet, initiate group stop with @signr
   * and participate in it.  If already set, participate in the existing
   * group stop.  If participated in a group stop (and thus slept), %true is
   * returned with siglock released.
   *
   * If ptraced, this function doesn't handle stop itself.  Instead,
   * %JOBCTL_TRAP_STOP is scheduled and %false is returned with siglock
   * untouched.  The caller must ensure that INTERRUPT trap handling takes
   * places afterwards.
   *
   * CONTEXT:
   * Must be called with @current->sighand->siglock held, which is released
   * on %true return.
   *
   * RETURNS:
   * %false if group stop is already cancelled or ptrace trap is scheduled.
   * %true if participated in group stop.
   */
  static bool do_signal_stop(int signr)
          __releases(&current->sighand->siglock)
  {
          struct signal_struct *sig = current->signal;
  
          if (!(current->jobctl & JOBCTL_STOP_PENDING)) {
                  unsigned int gstop = JOBCTL_STOP_PENDING | JOBCTL_STOP_CONSUME;
                  struct task_struct *t;
  
                  /* signr will be recorded in task->jobctl for retries */
                  WARN_ON_ONCE(signr & ~JOBCTL_STOP_SIGMASK);
  
                  if (!likely(current->jobctl & JOBCTL_STOP_DEQUEUED) ||
                      unlikely(signal_group_exit(sig)))
                          return false;
                  /*
                   * There is no group stop already in progress.  We must
                   * initiate one now.
                   *
                   * While ptraced, a task may be resumed while group stop is
                   * still in effect and then receive a stop signal and
                   * initiate another group stop.  This deviates from the
                   * usual behavior as two consecutive stop signals can't
                   * cause two group stops when !ptraced.  That is why we
                   * also check !task_is_stopped(t) below.
                   *
                   * The condition can be distinguished by testing whether
                   * SIGNAL_STOP_STOPPED is already set.  Don't generate
                   * group_exit_code in such case.
                   *
                   * This is not necessary for SIGNAL_STOP_CONTINUED because
                   * an intervening stop signal is required to cause two
                   * continued events regardless of ptrace.
                   */
                  if (!(sig->flags & SIGNAL_STOP_STOPPED))
                          sig->group_exit_code = signr;
  
                  sig->group_stop_count = 0;
  
                  if (task_set_jobctl_pending(current, signr | gstop))
                          sig->group_stop_count++;
  
                  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 (!task_is_stopped(t) &&
                              task_set_jobctl_pending(t, signr | gstop)) {
                                  sig->group_stop_count++;
                                  if (likely(!(t->ptrace & PT_SEIZED)))
                                          signal_wake_up(t, 0);
                                  else
                                          ptrace_trap_notify(t);
                          }
                  }
          }
  
          if (likely(!current->ptrace)) {
                  int notify = 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.
                   */
                  if (task_participate_group_stop(current))
                          notify = CLD_STOPPED;
  
                  __set_current_state(TASK_STOPPED);
                  spin_unlock_irq(&current->sighand->siglock);
  
                  /*
                   * Notify the parent of the group stop completion.  Because
                   * we're not holding either the siglock or tasklist_lock
                   * here, ptracer may attach inbetween; however, this is for
                   * group stop and should always be delivered to the real
                   * parent of the group leader.  The new ptracer will get
                   * its notification when this task transitions into
                   * TASK_TRACED.
                   */
                  if (notify) {
                          read_lock(&tasklist_lock);
                          do_notify_parent_cldstop(current, false, notify);
                          read_unlock(&tasklist_lock);
                  }
  
                  /* Now we don't run again until woken by SIGCONT or SIGKILL */
                  freezable_schedule();
                  return true;
          } else {
                  /*
                   * While ptraced, group stop is handled by STOP trap.
                   * Schedule it and let the caller deal with it.
                   */
                  task_set_jobctl_pending(current, JOBCTL_TRAP_STOP);
                  return false;
          }
  }
  
  /**
   * do_jobctl_trap - take care of ptrace jobctl traps
   *
   * When PT_SEIZED, it's used for both group stop and explicit
   * SEIZE/INTERRUPT traps.  Both generate PTRACE_EVENT_STOP trap with
   * accompanying siginfo.  If stopped, lower eight bits of exit_code contain
   * the stop signal; otherwise, %SIGTRAP.
   *
   * When !PT_SEIZED, it's used only for group stop trap with stop signal
   * number as exit_code and no siginfo.
   *
   * CONTEXT:
   * Must be called with @current->sighand->siglock held, which may be
   * released and re-acquired before returning with intervening sleep.
   */
  static void do_jobctl_trap(void)
  {
          struct signal_struct *signal = current->signal;
          int signr = current->jobctl & JOBCTL_STOP_SIGMASK;
  
          if (current->ptrace & PT_SEIZED) {
                  if (!signal->group_stop_count &&
                      !(signal->flags & SIGNAL_STOP_STOPPED))
                          signr = SIGTRAP;
                  WARN_ON_ONCE(!signr);
                  ptrace_do_notify(signr, signr | (PTRACE_EVENT_STOP << 8),
                                   CLD_STOPPED);
          } else {
                  WARN_ON_ONCE(!signr);
                  ptrace_stop(signr, CLD_STOPPED, 0, NULL);
                  current->exit_code = 0;
          }
  }
  
  static int ptrace_signal(int signr, siginfo_t *info)
  {
          ptrace_signal_deliver();
          /*
           * We do not check sig_kernel_stop(signr) but set this marker
           * unconditionally because we do not know whether debugger will
           * change signr. This flag has no meaning unless we are going
           * to stop after return from ptrace_stop(). In this case it will
           * be checked in do_signal_stop(), we should only stop if it was
           * not cleared by SIGCONT while we were sleeping. See also the
           * comment in dequeue_signal().
           */
          current->jobctl |= JOBCTL_STOP_DEQUEUED;
          ptrace_stop(signr, CLD_TRAPPED, 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;
                  rcu_read_lock();
                  info->si_pid = task_pid_vnr(current->parent);
                  info->si_uid = from_kuid_munged(current_user_ns(),
                                                  task_uid(current->parent));
                  rcu_read_unlock();
          }
  
          /* 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;
  
          if (unlikely(current->task_works))
                  task_work_run();
  
          if (unlikely(uprobe_deny_signal()))
                  return 0;
  
          /*
           * Do this once, we can't return to user-mode if freezing() == T.
           * do_signal_stop() and ptrace_stop() do freezable_schedule() and
           * thus do not need another check after return.
           */
          try_to_freeze();
  
  relock:
          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;
  
                  if (signal->flags & SIGNAL_CLD_CONTINUED)
                          why = CLD_CONTINUED;
                  else
                          why = CLD_STOPPED;
  
                  signal->flags &= ~SIGNAL_CLD_MASK;
  
                  spin_unlock_irq(&sighand->siglock);
  
                  /*
                   * Notify the parent that we're continuing.  This event is
                   * always per-process and doesn't make whole lot of sense
                   * for ptracers, who shouldn't consume the state via
                   * wait(2) either, but, for backward compatibility, notify
                   * the ptracer of the group leader too unless it's gonna be
                   * a duplicate.
                   */
                  read_lock(&tasklist_lock);
                  do_notify_parent_cldstop(current, false, why);
  
                  if (ptrace_reparented(current->group_leader))
                          do_notify_parent_cldstop(current->group_leader,
                                                  true, why);
                  read_unlock(&tasklist_lock);
  
                  goto relock;
          }
  
          for (;;) {
                  struct k_sigaction *ka;
  
                  if (unlikely(current->jobctl & JOBCTL_STOP_PENDING) &&
                      do_signal_stop(0))
                          goto relock;
  
                  if (unlikely(current->jobctl & JOBCTL_TRAP_MASK)) {
                          do_jobctl_trap();
                          spin_unlock_irq(&sighand->siglock);
                          goto relock;
                  }
  
                  signr = dequeue_signal(current, &current->blocked, info);
  
                  if (!signr)
                          break; /* will return 0 */
  
                  if (unlikely(current->ptrace) && signr != SIGKILL) {
                          signr = ptrace_signal(signr, info);
                          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(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);
                  }
  
                  /*
                   * Death signals, no core dump.
                   */
                  do_group_exit(info->si_signo);
                  /* NOTREACHED */
          }
          spin_unlock_irq(&sighand->siglock);
          return signr;
  }
  
  /**
   * signal_delivered - 
   * @sig:                number of signal being delivered
   * @info:               siginfo_t of signal being delivered
   * @ka:                 sigaction setting that chose the handler
   * @regs:               user register state
   * @stepping:           nonzero if debugger single-step or block-step in use
   *
   * This function should be called when a signal has succesfully been
   * delivered. It updates the blocked signals accordingly (@ka->sa.sa_mask
   * is always blocked, and the signal itself is blocked unless %SA_NODEFER
   * is set in @ka->sa.sa_flags.  Tracing is notified.
   */
  void signal_delivered(int sig, siginfo_t *info, struct k_sigaction *ka,
                          struct pt_regs *regs, int stepping)
  {
          sigset_t blocked;
  
          /* A signal was successfully delivered, and the
             saved sigmask was stored on the signal frame,
             and will be restored by sigreturn.  So we can
             simply clear the restore sigmask flag.  */
          clear_restore_sigmask();
  
          sigorsets(&blocked, &current->blocked, &ka->sa.sa_mask);
          if (!(ka->sa.sa_flags & SA_NODEFER))
                  sigaddset(&blocked, sig);
          set_current_blocked(&blocked);
          tracehook_signal_handler(sig, info, ka, regs, stepping);
  }
  
  /*
   * It could be that complete_signal() picked us to notify about the
   * group-wide signal. Other threads should be notified now to take
   * the shared signals in @which since we will not.
   */
  static void retarget_shared_pending(struct task_struct *tsk, sigset_t *which)
  {
          sigset_t retarget;
          struct task_struct *t;
  
          sigandsets(&retarget, &tsk->signal->shared_pending.signal, which);
          if (sigisemptyset(&retarget))
                  return;
  
          t = tsk;
          while_each_thread(tsk, t) {
                  if (t->flags & PF_EXITING)
                          continue;
  
                  if (!has_pending_signals(&retarget, &t->blocked))
                          continue;
                  /* Remove the signals this thread can handle. */
                  sigandsets(&retarget, &retarget, &t->blocked);
  
                  if (!signal_pending(t))
                          signal_wake_up(t, 0);
  
                  if (sigisemptyset(&retarget))
                          break;
          }
  }
  
  void exit_signals(struct task_struct *tsk)
  {
          int group_stop = 0;
          sigset_t unblocked;
  
          /*
           * @tsk is about to have PF_EXITING set - lock out users which
           * expect stable threadgroup.
           */
          threadgroup_change_begin(tsk);
  
          if (thread_group_empty(tsk) || signal_group_exit(tsk->signal)) {
                  tsk->flags |= PF_EXITING;
                  threadgroup_change_end(tsk);
                  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;
  
          threadgroup_change_end(tsk);
  
          if (!signal_pending(tsk))
                  goto out;
  
          unblocked = tsk->blocked;
          signotset(&unblocked);
          retarget_shared_pending(tsk, &unblocked);
  
          if (unlikely(tsk->jobctl & JOBCTL_STOP_PENDING) &&
              task_participate_group_stop(tsk))
                  group_stop = CLD_STOPPED;
  out:
          spin_unlock_irq(&tsk->sighand->siglock);
  
          /*
           * If group stop has completed, deliver the notification.  This
           * should always go to the real parent of the group leader.
           */
          if (unlikely(group_stop)) {
                  read_lock(&tasklist_lock);
                  do_notify_parent_cldstop(tsk, false, 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;
  }
  
  static void __set_task_blocked(struct task_struct *tsk, const sigset_t *newset)
  {
          if (signal_pending(tsk) && !thread_group_empty(tsk)) {
                  sigset_t newblocked;
                  /* A set of now blocked but previously unblocked signals. */
                  sigandnsets(&newblocked, newset, &current->blocked);
                  retarget_shared_pending(tsk, &newblocked);
          }
          tsk->blocked = *newset;
          recalc_sigpending();
  }
  
  /**
   * set_current_blocked - change current->blocked mask
   * @newset: new mask
   *
   * It is wrong to change ->blocked directly, this helper should be used
   * to ensure the process can't miss a shared signal we are going to block.
   */
  void set_current_blocked(sigset_t *newset)
  {
          sigdelsetmask(newset, sigmask(SIGKILL) | sigmask(SIGSTOP));
          __set_current_blocked(newset);
  }
  
  void __set_current_blocked(const sigset_t *newset)
  {
          struct task_struct *tsk = current;
  
          spin_lock_irq(&tsk->sighand->siglock);
          __set_task_blocked(tsk, newset);
          spin_unlock_irq(&tsk->sighand->siglock);
  }
  
  /*
   * 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)
  {
          struct task_struct *tsk = current;
          sigset_t newset;
  
          /* Lockless, only current can change ->blocked, never from irq */
          if (oldset)
                  *oldset = tsk->blocked;
  
          switch (how) {
          case SIG_BLOCK:
                  sigorsets(&newset, &tsk->blocked, set);
                  break;
          case SIG_UNBLOCK:
                  sigandnsets(&newset, &tsk->blocked, set);
                  break;
          case SIG_SETMASK:
                  newset = *set;
                  break;
          default:
                  return -EINVAL;
          }
  
          __set_current_blocked(&newset);
          return 0;
  }
  
  /**
   *  sys_rt_sigprocmask - change the list of currently blocked signals
   *  @how: whether to add, remove, or set signals
   *  @nset: 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 *, nset,
                  sigset_t __user *, oset, size_t, sigsetsize)
  {
          sigset_t old_set, new_set;
          int error;
  
          /* XXX: Don't preclude handling different sized sigset_t's.  */
          if (sigsetsize != sizeof(sigset_t))
                  return -EINVAL;
  
          old_set = current->blocked;
  
          if (nset) {
                  if (copy_from_user(&new_set, nset, sizeof(sigset_t)))
                          return -EFAULT;
                  sigdelsetmask(&new_set, sigmask(SIGKILL)|sigmask(SIGSTOP));
  
                  error = sigprocmask(how, &new_set, NULL);
                  if (error)
                          return error;
          }
  
          if (oset) {
                  if (copy_to_user(oset, &old_set, sizeof(sigset_t)))
                          return -EFAULT;
          }
  
          return 0;
  }
  
  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;
  #ifdef __ARCH_SIGSYS
          case __SI_SYS:
                  err |= __put_user(from->si_call_addr, &to->si_call_addr);
                  err |= __put_user(from->si_syscall, &to->si_syscall);
                  err |= __put_user(from->si_arch, &to->si_arch);
                  break;
  #endif
          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
  
  /**
   *  do_sigtimedwait - wait for queued signals specified in @which
   *  @which: queued signals to wait for
   *  @info: if non-null, the signal's siginfo is returned here
   *  @ts: upper bound on process time suspension
   */
  int do_sigtimedwait(const sigset_t *which, siginfo_t *info,
                          const struct timespec *ts)
  {
          struct task_struct *tsk = current;
          long timeout = MAX_SCHEDULE_TIMEOUT;
          sigset_t mask = *which;
          int sig;
  
          if (ts) {
                  if (!timespec_valid(ts))
                          return -EINVAL;
                  timeout = timespec_to_jiffies(ts);
                  /*
                   * We can be close to the next tick, add another one
                   * to ensure we will wait at least the time asked for.
                   */
                  if (ts->tv_sec || ts->tv_nsec)
                          timeout++;
          }
  
          /*
           * Invert the set of allowed signals to get those we want to block.
           */
          sigdelsetmask(&mask, sigmask(SIGKILL) | sigmask(SIGSTOP));
          signotset(&mask);
  
          spin_lock_irq(&tsk->sighand->siglock);
          sig = dequeue_signal(tsk, &mask, info);
          if (!sig && timeout) {
                  /*
                   * None ready, temporarily unblock those we're interested
                   * while we are sleeping in so that we'll be awakened when
                   * they arrive. Unblocking is always fine, we can avoid
                   * set_current_blocked().
                   */
                  tsk->real_blocked = tsk->blocked;
                  sigandsets(&tsk->blocked, &tsk->blocked, &mask);
                  recalc_sigpending();
                  spin_unlock_irq(&tsk->sighand->siglock);
  
                  timeout = schedule_timeout_interruptible(timeout);
  
                  spin_lock_irq(&tsk->sighand->siglock);
                  __set_task_blocked(tsk, &tsk->real_blocked);
                  siginitset(&tsk->real_blocked, 0);
                  sig = dequeue_signal(tsk, &mask, info);
          }
          spin_unlock_irq(&tsk->sighand->siglock);
  
          if (sig)
                  return sig;
          return timeout ? -EINTR : -EAGAIN;
  }
  
  /**
   *  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)
  {
          sigset_t these;
          struct timespec ts;
          siginfo_t info;
          int ret;
  
          /* 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;
  
          if (uts) {
                  if (copy_from_user(&ts, uts, sizeof(ts)))
                          return -EFAULT;
          }
  
          ret = do_sigtimedwait(&these, &info, uts ? &ts : NULL);
  
          if (ret > 0 && uinfo) {
                  if (copy_siginfo_to_user(uinfo, &info))
                          ret = -EFAULT;
          }
  
          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 = from_kuid_munged(current_user_ns(), 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 = from_kuid_munged(current_user_ns(), 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 CONFIG_GENERIC_SIGALTSTACK
  SYSCALL_DEFINE2(sigaltstack,const stack_t __user *,uss, stack_t __user *,uoss)
  {
          return do_sigaltstack(uss, uoss, current_user_stack_pointer());
  }
  #endif
  
  int restore_altstack(const stack_t __user *uss)
  {
          int err = do_sigaltstack(uss, NULL, current_user_stack_pointer());
          /* squash all but EFAULT for now */
          return err == -EFAULT ? err : 0;
  }
  
  int __save_altstack(stack_t __user *uss, unsigned long sp)
  {
          struct task_struct *t = current;
          return  __put_user((void __user *)t->sas_ss_sp, &uss->ss_sp) |
                  __put_user(sas_ss_flags(sp), &uss->ss_flags) |
                  __put_user(t->sas_ss_size, &uss->ss_size);
  }
  
  #ifdef CONFIG_COMPAT
  #ifdef CONFIG_GENERIC_SIGALTSTACK
  COMPAT_SYSCALL_DEFINE2(sigaltstack,
                          const compat_stack_t __user *, uss_ptr,
                          compat_stack_t __user *, uoss_ptr)
  {
          stack_t uss, uoss;
          int ret;
          mm_segment_t seg;
  
          if (uss_ptr) {
                  compat_stack_t uss32;
  
                  memset(&uss, 0, sizeof(stack_t));
                  if (copy_from_user(&uss32, uss_ptr, sizeof(compat_stack_t)))
                          return -EFAULT;
                  uss.ss_sp = compat_ptr(uss32.ss_sp);
                  uss.ss_flags = uss32.ss_flags;
                  uss.ss_size = uss32.ss_size;
          }
          seg = get_fs();
          set_fs(KERNEL_DS);
          ret = do_sigaltstack((stack_t __force __user *) (uss_ptr ? &uss : NULL),
                               (stack_t __force __user *) &uoss,
                               compat_user_stack_pointer());
          set_fs(seg);
          if (ret >= 0 && uoss_ptr)  {
                  if (!access_ok(VERIFY_WRITE, uoss_ptr, sizeof(compat_stack_t)) ||
                      __put_user(ptr_to_compat(uoss.ss_sp), &uoss_ptr->ss_sp) ||
                      __put_user(uoss.ss_flags, &uoss_ptr->ss_flags) ||
                      __put_user(uoss.ss_size, &uoss_ptr->ss_size))
                          ret = -EFAULT;
          }
          return ret;
  }
  
  int compat_restore_altstack(const compat_stack_t __user *uss)
  {
          int err = compat_sys_sigaltstack(uss, NULL);
          /* squash all but -EFAULT for now */
          return err == -EFAULT ? err : 0;
  }
  
  int __compat_save_altstack(compat_stack_t __user *uss, unsigned long sp)
  {
          struct task_struct *t = current;
          return  __put_user(ptr_to_compat((void __user *)t->sas_ss_sp), &uss->ss_sp) |
                  __put_user(sas_ss_flags(sp), &uss->ss_flags) |
                  __put_user(t->sas_ss_size, &uss->ss_size);
  }
  #endif
  #endif
  
  #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
   *  @nset: 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 *, nset,
                  old_sigset_t __user *, oset)
  {
          old_sigset_t old_set, new_set;
          sigset_t new_blocked;
  
          old_set = current->blocked.sig[0];
  
          if (nset) {
                  if (copy_from_user(&new_set, nset, sizeof(*nset)))
                          return -EFAULT;
  
                  new_blocked = current->blocked;
  
                  switch (how) {
                  case SIG_BLOCK:
                          sigaddsetmask(&new_blocked, new_set);
                          break;
                  case SIG_UNBLOCK:
                          sigdelsetmask(&new_blocked, new_set);
                          break;
                  case SIG_SETMASK:
                          new_blocked.sig[0] = new_set;
                          break;
                  default:
                          return -EINVAL;
                  }
  
                  set_current_blocked(&new_blocked);
          }
  
          if (oset) {
                  if (copy_to_user(oset, &old_set, sizeof(*oset)))
                          return -EFAULT;
          }
  
          return 0;
  }
  #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 = current->blocked.sig[0];
          sigset_t newset;
  
          siginitset(&newset, newmask);
          set_current_blocked(&newset);
  
          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)
  {
          while (!signal_pending(current)) {
                  current->state = TASK_INTERRUPTIBLE;
                  schedule();
          }
          return -ERESTARTNOHAND;
  }
  
  #endif
  
  int sigsuspend(sigset_t *set)
  {
          current->saved_sigmask = current->blocked;
          set_current_blocked(set);
  
          current->state = TASK_INTERRUPTIBLE;
          schedule();
          set_restore_sigmask();
          return -ERESTARTNOHAND;
  }
  
  #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;
          return sigsuspend(&newset);
  }
  #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 */