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

  #include <linux/slab.h>
  #include <linux/module.h>

  #include <linux/init.h>
  #include <linux/sched.h>
  #include <linux/fs.h>
  #include <linux/tty.h>
  #include <linux/binfmts.h>
  #include <linux/security.h>
  #include <linux/syscalls.h>
  #include <linux/ptrace.h>

  #include <linux/signal.h>

  #include <linux/signalfd.h>

  #include <linux/tracehook.h>

  #include <linux/capability.h>

  #include <linux/freezer.h>

  #include <linux/pid_namespace.h>
  #include <linux/nsproxy.h>

  #include <trace/sched.h>

  #include <asm/param.h>
  #include <asm/uaccess.h>
  #include <asm/unistd.h>
  #include <asm/siginfo.h>

  #include "audit.h"	/* audit_signal_info() */

  
  /*
   * SLAB caches for signal bits.
   */

  static struct kmem_cache *sigqueue_cachep;

  DEFINE_TRACE(sched_signal_send);

  static void __user *sig_handler(struct task_struct *t, int sig)

  {

  	return t->sighand->action[sig - 1].sa.sa_handler;
  }

  static int sig_handler_ignored(void __user *handler, int sig)
  {

  	/* Is it explicitly or implicitly ignored? */

  	return handler == SIG_IGN ||
  		(handler == SIG_DFL && sig_kernel_ignore(sig));
  }

  static int sig_task_ignored(struct task_struct *t, int sig,
  		int from_ancestor_ns)

  {

  	void __user *handler;

  	handler = sig_handler(t, sig);
  
  	if (unlikely(t->signal->flags & SIGNAL_UNKILLABLE) &&

  			handler == SIG_DFL && !from_ancestor_ns)

  		return 1;
  
  	return sig_handler_ignored(handler, sig);
  }

  static int sig_ignored(struct task_struct *t, int sig, int from_ancestor_ns)

  {

  	/*
  	 * Blocked signals are never ignored, since the
  	 * signal handler may change by the time it is
  	 * unblocked.
  	 */

  	if (sigismember(&t->blocked, sig) || sigismember(&t->real_blocked, sig))

  		return 0;

  	if (!sig_task_ignored(t, sig, from_ancestor_ns))

  		return 0;
  
  	/*
  	 * Tracers may want to know about even ignored signals.
  	 */

  	return !tracehook_consider_ignored_signal(t, sig);

  }
  
  /*
   * Re-calculate pending state from the set of locally pending
   * signals, globally pending signals, and blocked signals.
   */
  static inline int has_pending_signals(sigset_t *signal, sigset_t *blocked)
  {
  	unsigned long ready;
  	long i;
  
  	switch (_NSIG_WORDS) {
  	default:
  		for (i = _NSIG_WORDS, ready = 0; --i >= 0 ;)
  			ready |= signal->sig[i] &~ blocked->sig[i];
  		break;
  
  	case 4: ready  = signal->sig[3] &~ blocked->sig[3];
  		ready |= signal->sig[2] &~ blocked->sig[2];
  		ready |= signal->sig[1] &~ blocked->sig[1];
  		ready |= signal->sig[0] &~ blocked->sig[0];
  		break;
  
  	case 2: ready  = signal->sig[1] &~ blocked->sig[1];
  		ready |= signal->sig[0] &~ blocked->sig[0];
  		break;
  
  	case 1: ready  = signal->sig[0] &~ blocked->sig[0];
  	}
  	return ready !=	0;
  }
  
  #define PENDING(p,b) has_pending_signals(&(p)->signal, (b))

  static int recalc_sigpending_tsk(struct task_struct *t)

  {
  	if (t->signal->group_stop_count > 0 ||
  	    PENDING(&t->pending, &t->blocked) ||

  	    PENDING(&t->signal->shared_pending, &t->blocked)) {

  		set_tsk_thread_flag(t, TIF_SIGPENDING);

  		return 1;
  	}

  	/*
  	 * We must never clear the flag in another thread, or in current
  	 * when it's possible the current syscall is returning -ERESTART*.
  	 * So we don't clear it here, and only callers who know they should do.
  	 */

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

  }
  
  void recalc_sigpending(void)
  {

  	if (unlikely(tracehook_force_sigpending()))
  		set_thread_flag(TIF_SIGPENDING);
  	else if (!recalc_sigpending_tsk(current) && !freezing(current))

  		clear_thread_flag(TIF_SIGPENDING);

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

  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;
  	switch (_NSIG_WORDS) {
  	default:
  		for (i = 0; i < _NSIG_WORDS; ++i, ++s, ++m)
  			if ((x = *s &~ *m) != 0) {
  				sig = ffz(~x) + i*_NSIG_BPW + 1;
  				break;
  			}
  		break;
  
  	case 2: if ((x = s[0] &~ m[0]) != 0)
  			sig = 1;
  		else if ((x = s[1] &~ m[1]) != 0)
  			sig = _NSIG_BPW + 1;
  		else
  			break;
  		sig += ffz(~x);
  		break;
  
  	case 1: if ((x = *s &~ *m) != 0)
  			sig = ffz(~x) + 1;
  		break;
  	}
  	
  	return sig;
  }

  /*
   * allocate a new signal queue record
   * - this may be called without locks if and only if t == current, otherwise an

   *   appopriate lock must be held to stop the target task from exiting

   */

  static struct sigqueue *__sigqueue_alloc(struct task_struct *t, gfp_t flags,

  					 int override_rlimit)
  {
  	struct sigqueue *q = NULL;

  	struct user_struct *user;

  	/*

  	 * We won't get problems with the target's UID changing under us
  	 * because changing it requires RCU be used, and if t != current, the
  	 * caller must be holding the RCU readlock (by way of a spinlock) and
  	 * we use RCU protection here

  	 */

  	user = get_uid(__task_cred(t)->user);

  	atomic_inc(&user->sigpending);

  	if (override_rlimit ||

  	    atomic_read(&user->sigpending) <=

  			t->signal->rlim[RLIMIT_SIGPENDING].rlim_cur)
  		q = kmem_cache_alloc(sigqueue_cachep, flags);
  	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)

  {
  	unsigned long flags;
  
  	spin_lock_irqsave(&t->sighand->siglock, flags);

  	clear_tsk_thread_flag(t, TIF_SIGPENDING);

  	flush_sigqueue(&t->pending);
  	flush_sigqueue(&t->signal->shared_pending);
  	spin_unlock_irqrestore(&t->sighand->siglock, flags);
  }

  static void __flush_itimer_signals(struct sigpending *pending)
  {
  	sigset_t signal, retain;
  	struct sigqueue *q, *n;
  
  	signal = pending->signal;
  	sigemptyset(&retain);
  
  	list_for_each_entry_safe(q, n, &pending->list, list) {
  		int sig = q->info.si_signo;
  
  		if (likely(q->info.si_code != SI_TIMER)) {
  			sigaddset(&retain, sig);
  		} else {
  			sigdelset(&signal, sig);
  			list_del_init(&q->list);
  			__sigqueue_free(q);
  		}
  	}
  
  	sigorsets(&pending->signal, &signal, &retain);
  }
  
  void flush_itimer_signals(void)
  {
  	struct task_struct *tsk = current;
  	unsigned long flags;
  
  	spin_lock_irqsave(&tsk->sighand->siglock, flags);
  	__flush_itimer_signals(&tsk->pending);
  	__flush_itimer_signals(&tsk->signal->shared_pending);
  	spin_unlock_irqrestore(&tsk->sighand->siglock, flags);
  }

  void ignore_signals(struct task_struct *t)
  {
  	int i;
  
  	for (i = 0; i < _NSIG; ++i)
  		t->sighand->action[i].sa.sa_handler = SIG_IGN;
  
  	flush_signals(t);
  }

  /*

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

  int unhandled_signal(struct task_struct *tsk, int sig)
  {

  	void __user *handler = tsk->sighand->action[sig-1].sa.sa_handler;

  	if (is_global_init(tsk))

  		return 1;

  	if (handler != SIG_IGN && handler != SIG_DFL)

  		return 0;

  	return !tracehook_consider_fatal_signal(tsk, sig);

  }

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

  static void collect_signal(int sig, struct sigpending *list, siginfo_t *info)

  {
  	struct sigqueue *q, *first = NULL;

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

  			if (first)
  				goto still_pending;

  			first = q;
  		}
  	}

  
  	sigdelset(&list->signal, sig);

  	if (first) {

  still_pending:

  		list_del_init(&first->list);
  		copy_siginfo(info, &first->info);
  		__sigqueue_free(first);

  	} else {

  		/* Ok, it wasn't in the queue.  This must be
  		   a fast-pathed signal or we must have been
  		   out of queue space.  So zero out the info.
  		 */

  		info->si_signo = sig;
  		info->si_errno = 0;
  		info->si_code = 0;
  		info->si_pid = 0;
  		info->si_uid = 0;
  	}

  }
  
  static int __dequeue_signal(struct sigpending *pending, sigset_t *mask,
  			siginfo_t *info)
  {

  	int sig = next_signal(pending, mask);

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

  		collect_signal(sig, pending, info);

  	}

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

  	int signr;

  
  	/* We only dequeue private signals from ourselves, we don't let
  	 * signalfd steal them
  	 */

  	signr = __dequeue_signal(&tsk->pending, mask, info);

  	if (!signr) {

  		signr = __dequeue_signal(&tsk->signal->shared_pending,
  					 mask, info);

  		/*
  		 * itimer signal ?
  		 *
  		 * itimers are process shared and we restart periodic
  		 * itimers in the signal delivery path to prevent DoS
  		 * attacks in the high resolution timer case. This is
  		 * compliant with the old way of self restarting
  		 * itimers, as the SIGALRM is a legacy signal and only
  		 * queued once. Changing the restart behaviour to
  		 * restart the timer in the signal dequeue path is
  		 * reducing the timer noise on heavy loaded !highres
  		 * systems too.
  		 */
  		if (unlikely(signr == SIGALRM)) {
  			struct hrtimer *tmr = &tsk->signal->real_timer;
  
  			if (!hrtimer_is_queued(tmr) &&
  			    tsk->signal->it_real_incr.tv64 != 0) {
  				hrtimer_forward(tmr, tmr->base->get_time(),
  						tsk->signal->it_real_incr);
  				hrtimer_restart(tmr);
  			}
  		}
  	}

  	recalc_sigpending();

  	if (!signr)
  		return 0;
  
  	if (unlikely(sig_kernel_stop(signr))) {

  		/*
  		 * Set a marker that we have dequeued a stop signal.  Our
  		 * caller might release the siglock and then the pending
  		 * stop signal it is about to process is no longer in the
  		 * pending bitmasks, but must still be cleared by a SIGCONT
  		 * (and overruled by a SIGKILL).  So those cases clear this
  		 * shared flag after we've set it.  Note that this flag may
  		 * remain set after the signal we return is ignored or
  		 * handled.  That doesn't matter because its only purpose
  		 * is to alert stop-signal processing code when another
  		 * processor has come along and cleared the flag.
  		 */

  		tsk->signal->flags |= SIGNAL_STOP_DEQUEUED;

  	}

  	if ((info->si_code & __SI_MASK) == __SI_TIMER && info->si_sys_private) {

  		/*
  		 * Release the siglock to ensure proper locking order
  		 * of timer locks outside of siglocks.  Note, we leave
  		 * irqs disabled here, since the posix-timers code is
  		 * about to disable them again anyway.
  		 */
  		spin_unlock(&tsk->sighand->siglock);
  		do_schedule_next_timer(info);
  		spin_lock(&tsk->sighand->siglock);
  	}
  	return signr;
  }
  
  /*
   * Tell a process that it has a new active signal..
   *
   * NOTE! we rely on the previous spin_lock to
   * lock interrupts for us! We can only be called with
   * "siglock" held, and the local interrupt must
   * have been disabled when that got acquired!
   *
   * No need to set need_resched since signal event passing
   * goes through ->blocked
   */
  void signal_wake_up(struct task_struct *t, int resume)
  {
  	unsigned int mask;
  
  	set_tsk_thread_flag(t, TIF_SIGPENDING);
  
  	/*

  	 * For SIGKILL, we want to wake it up in the stopped/traced/killable
  	 * case. We don't check t->state here because there is a race with it

  	 * executing another processor and just now entering stopped state.
  	 * By using wake_up_state, we ensure the process will wake up and
  	 * handle its death signal.
  	 */
  	mask = TASK_INTERRUPTIBLE;
  	if (resume)

  		mask |= TASK_WAKEKILL;

  	if (!wake_up_state(t, mask))
  		kick_process(t);
  }
  
  /*
   * Remove signals in mask from the pending set and queue.
   * Returns 1 if any signals were found.
   *
   * All callers must be holding the siglock.

   *
   * This version takes a sigset mask and looks at all signals,
   * not just those in the first mask word.
   */
  static int rm_from_queue_full(sigset_t *mask, struct sigpending *s)
  {
  	struct sigqueue *q, *n;
  	sigset_t m;
  
  	sigandsets(&m, mask, &s->signal);
  	if (sigisemptyset(&m))
  		return 0;
  
  	signandsets(&s->signal, &s->signal, mask);
  	list_for_each_entry_safe(q, n, &s->list, list) {
  		if (sigismember(mask, q->info.si_signo)) {
  			list_del_init(&q->list);
  			__sigqueue_free(q);
  		}
  	}
  	return 1;
  }
  /*
   * Remove signals in mask from the pending set and queue.
   * Returns 1 if any signals were found.
   *
   * All callers must be holding the siglock.

   */
  static int rm_from_queue(unsigned long mask, struct sigpending *s)
  {
  	struct sigqueue *q, *n;
  
  	if (!sigtestsetmask(&s->signal, mask))
  		return 0;
  
  	sigdelsetmask(&s->signal, mask);
  	list_for_each_entry_safe(q, n, &s->list, list) {
  		if (q->info.si_signo < SIGRTMIN &&
  		    (mask & sigmask(q->info.si_signo))) {
  			list_del_init(&q->list);
  			__sigqueue_free(q);
  		}
  	}
  	return 1;
  }
  
  /*
   * Bad permissions for sending the signal

   * - the caller must hold at least the RCU read lock

   */
  static int check_kill_permission(int sig, struct siginfo *info,
  				 struct task_struct *t)
  {

  	const struct cred *cred = current_cred(), *tcred;

  	struct pid *sid;

  	int error;

  	if (!valid_signal(sig))

  		return -EINVAL;
  
  	if (info != SEND_SIG_NOINFO && (is_si_special(info) || SI_FROMKERNEL(info)))
  		return 0;

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

  		return error;

  	tcred = __task_cred(t);
  	if ((cred->euid ^ tcred->suid) &&
  	    (cred->euid ^ tcred->uid) &&
  	    (cred->uid  ^ tcred->suid) &&
  	    (cred->uid  ^ tcred->uid) &&

  	    !capable(CAP_KILL)) {
  		switch (sig) {
  		case SIGCONT:

  			sid = task_session(t);

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

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

  }

  /*

   * Handle magic process-wide effects of stop/continue signals. Unlike
   * the signal actions, these happen immediately at signal-generation

   * time regardless of blocking, ignoring, or handling.  This does the
   * actual continuing for SIGCONT, but not the actual stopping for stop

   * signals. The process stop is done as a signal action for SIG_DFL.
   *
   * Returns true if the signal should be actually delivered, otherwise
   * it should be dropped.

   */

  static int prepare_signal(int sig, struct task_struct *p, int from_ancestor_ns)

  {

  	struct signal_struct *signal = p->signal;

  	struct task_struct *t;

  	if (unlikely(signal->flags & SIGNAL_GROUP_EXIT)) {

  		/*

  		 * The process is in the middle of dying, nothing to do.

  		 */

  	} else if (sig_kernel_stop(sig)) {

  		/*
  		 * This is a stop signal.  Remove SIGCONT from all queues.
  		 */

  		rm_from_queue(sigmask(SIGCONT), &signal->shared_pending);

  		t = p;
  		do {
  			rm_from_queue(sigmask(SIGCONT), &t->pending);

  		} while_each_thread(p, t);

  	} else if (sig == SIGCONT) {

  		unsigned int why;

  		/*
  		 * Remove all stop signals from all queues,
  		 * and wake all threads.
  		 */

  		rm_from_queue(SIG_KERNEL_STOP_MASK, &signal->shared_pending);

  		t = p;
  		do {
  			unsigned int state;
  			rm_from_queue(SIG_KERNEL_STOP_MASK, &t->pending);

  			/*
  			 * If there is a handler for SIGCONT, we must make
  			 * sure that no thread returns to user mode before
  			 * we post the signal, in case it was the only
  			 * thread eligible to run the signal handler--then
  			 * it must not do anything between resuming and
  			 * running the handler.  With the TIF_SIGPENDING
  			 * flag set, the thread will pause and acquire the
  			 * siglock that we hold now and until we've queued

  			 * the pending signal.

  			 *
  			 * Wake up the stopped thread _after_ setting
  			 * TIF_SIGPENDING
  			 */

  			state = __TASK_STOPPED;

  			if (sig_user_defined(t, SIGCONT) && !sigismember(&t->blocked, SIGCONT)) {
  				set_tsk_thread_flag(t, TIF_SIGPENDING);
  				state |= TASK_INTERRUPTIBLE;
  			}
  			wake_up_state(t, state);

  		} while_each_thread(p, t);

  		/*
  		 * Notify the parent with CLD_CONTINUED if we were stopped.
  		 *
  		 * If we were in the middle of a group stop, we pretend it
  		 * was already finished, and then continued. Since SIGCHLD
  		 * doesn't queue we report only CLD_STOPPED, as if the next
  		 * CLD_CONTINUED was dropped.
  		 */
  		why = 0;

  		if (signal->flags & SIGNAL_STOP_STOPPED)

  			why |= SIGNAL_CLD_CONTINUED;

  		else if (signal->group_stop_count)

  			why |= SIGNAL_CLD_STOPPED;
  
  		if (why) {

  			/*
  			 * The first thread which returns from finish_stop()
  			 * will take ->siglock, notice SIGNAL_CLD_MASK, and
  			 * notify its parent. See get_signal_to_deliver().
  			 */

  			signal->flags = why | SIGNAL_STOP_CONTINUED;
  			signal->group_stop_count = 0;
  			signal->group_exit_code = 0;

  		} else {
  			/*
  			 * We are not stopped, but there could be a stop
  			 * signal in the middle of being processed after
  			 * being removed from the queue.  Clear that too.
  			 */

  			signal->flags &= ~SIGNAL_STOP_DEQUEUED;

  		}

  	}

  	return !sig_ignored(p, sig, from_ancestor_ns);

  }

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

  static void complete_signal(int sig, struct task_struct *p, int group)

  {
  	struct signal_struct *signal = p->signal;
  	struct task_struct *t;
  
  	/*
  	 * Now find a thread we can wake up to take the signal off the queue.
  	 *
  	 * If the main thread wants the signal, it gets first crack.
  	 * Probably the least surprising to the average bear.
  	 */
  	if (wants_signal(sig, p))
  		t = p;

  	else if (!group || thread_group_empty(p))

  		/*
  		 * There is just one thread and it does not need to be woken.
  		 * It will dequeue unblocked signals before it runs again.
  		 */
  		return;
  	else {
  		/*
  		 * Otherwise try to find a suitable thread.
  		 */
  		t = signal->curr_target;
  		while (!wants_signal(sig, t)) {
  			t = next_thread(t);
  			if (t == signal->curr_target)
  				/*
  				 * No thread needs to be woken.
  				 * Any eligible threads will see
  				 * the signal in the queue soon.
  				 */
  				return;
  		}
  		signal->curr_target = t;
  	}
  
  	/*
  	 * Found a killable thread.  If the signal will be fatal,
  	 * then start taking the whole group down immediately.
  	 */

  	if (sig_fatal(p, sig) &&
  	    !(signal->flags & (SIGNAL_UNKILLABLE | SIGNAL_GROUP_EXIT)) &&

  	    !sigismember(&t->real_blocked, sig) &&

  	    (sig == SIGKILL ||

  	     !tracehook_consider_fatal_signal(t, sig))) {

  		/*
  		 * This signal will be fatal to the whole group.
  		 */
  		if (!sig_kernel_coredump(sig)) {
  			/*
  			 * Start a group exit and wake everybody up.
  			 * This way we don't have other threads
  			 * running and doing things after a slower
  			 * thread has the fatal signal pending.
  			 */
  			signal->flags = SIGNAL_GROUP_EXIT;
  			signal->group_exit_code = sig;
  			signal->group_stop_count = 0;
  			t = p;
  			do {
  				sigaddset(&t->pending.signal, SIGKILL);
  				signal_wake_up(t, 1);
  			} while_each_thread(p, t);
  			return;
  		}
  	}
  
  	/*
  	 * The signal is already in the shared-pending queue.
  	 * Tell the chosen thread to wake up and dequeue it.
  	 */
  	signal_wake_up(t, sig == SIGKILL);
  	return;
  }

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

  static int __send_signal(int sig, struct siginfo *info, struct task_struct *t,
  			int group, int from_ancestor_ns)

  {

  	struct sigpending *pending;

  	struct sigqueue *q;

  	trace_sched_signal_send(sig, t);

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

  
  	if (!prepare_signal(sig, t, from_ancestor_ns))

  		return 0;

  
  	pending = group ? &t->signal->shared_pending : &t->pending;

  	/*

  	 * Short-circuit ignored signals and support queuing
  	 * exactly one non-rt signal, so that we can get more
  	 * detailed information about the cause of the signal.
  	 */

  	if (legacy_queue(pending, sig))

  		return 0;

  	/*

  	 * fast-pathed signals for kernel-internal things like SIGSTOP
  	 * or SIGKILL.
  	 */

  	if (info == SEND_SIG_FORCED)

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

  					     (is_si_special(info) ||

  					      info->si_code >= 0)));
  	if (q) {

  		list_add_tail(&q->list, &pending->list);

  		switch ((unsigned long) info) {

  		case (unsigned long) SEND_SIG_NOINFO:

  			q->info.si_signo = sig;
  			q->info.si_errno = 0;
  			q->info.si_code = SI_USER;

  			q->info.si_pid = task_tgid_nr_ns(current,

  							task_active_pid_ns(t));

  			q->info.si_uid = current_uid();

  			break;

  		case (unsigned long) SEND_SIG_PRIV:

  			q->info.si_signo = sig;
  			q->info.si_errno = 0;
  			q->info.si_code = SI_KERNEL;
  			q->info.si_pid = 0;
  			q->info.si_uid = 0;
  			break;
  		default:
  			copy_siginfo(&q->info, info);

  			if (from_ancestor_ns)
  				q->info.si_pid = 0;

  			break;
  		}

  	} else if (!is_si_special(info)) {
  		if (sig >= SIGRTMIN && info->si_code != SI_USER)

  		/*
  		 * Queue overflow, abort.  We may abort if the signal was rt
  		 * and sent by user using something other than kill().
  		 */
  			return -EAGAIN;

  	}
  
  out_set:

  	signalfd_notify(t, sig);

  	sigaddset(&pending->signal, sig);

  	complete_signal(sig, t, group);
  	return 0;

  }

  static int send_signal(int sig, struct siginfo *info, struct task_struct *t,
  			int group)
  {

  	int from_ancestor_ns = 0;
  
  #ifdef CONFIG_PID_NS
  	if (!is_si_special(info) && SI_FROMUSER(info) &&
  			task_pid_nr_ns(current, task_active_pid_ns(t)) <= 0)
  		from_ancestor_ns = 1;
  #endif
  
  	return __send_signal(sig, info, t, group, from_ancestor_ns);

  }

  int print_fatal_signals;
  
  static void print_fatal_signal(struct pt_regs *regs, int signr)
  {
  	printk("%s/%d: potentially unexpected fatal signal %d.
  ",

  		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;

  			__get_user(insn, (unsigned char *)(regs->ip + i));

  			printk("%02x ", insn);
  		}
  	}
  #endif
  	printk("
  ");

  	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);

  }
  
  /*
   * 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;
  }
  
  void
  force_sig_specific(int sig, struct task_struct *t)
  {

  	force_sig_info(sig, SEND_SIG_FORCED, t);

  }

  /*
   * Nuke all other threads in the group.
   */
  void zap_other_threads(struct task_struct *p)
  {
  	struct task_struct *t;

  	p->signal->group_stop_count = 0;

  	for (t = next_thread(p); t != p; t = next_thread(t)) {
  		/*
  		 * Don't bother with already dead threads
  		 */
  		if (t->exit_state)
  			continue;

  		/* SIGKILL will be handled before any pending SIGSTOP */

  		sigaddset(&t->pending.signal, SIGKILL);

  		signal_wake_up(t, 1);
  	}
  }

  int __fatal_signal_pending(struct task_struct *tsk)

  {
  	return sigismember(&tsk->pending.signal, SIGKILL);
  }

  EXPORT_SYMBOL(__fatal_signal_pending);

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

  	rcu_read_lock();

  	for (;;) {
  		sighand = rcu_dereference(tsk->sighand);
  		if (unlikely(sighand == NULL))
  			break;
  
  		spin_lock_irqsave(&sighand->siglock, *flags);
  		if (likely(sighand == tsk->sighand))
  			break;
  		spin_unlock_irqrestore(&sighand->siglock, *flags);
  	}

  	rcu_read_unlock();

  
  	return sighand;
  }

  /*
   * send signal info to all the members of a group
   * - the caller must hold the RCU read lock at least
   */

  int group_send_sig_info(int sig, struct siginfo *info, struct task_struct *p)
  {
  	unsigned long flags;
  	int ret;
  
  	ret = check_kill_permission(sig, info, p);

  
  	if (!ret && sig) {
  		ret = -ESRCH;
  		if (lock_task_sighand(p, &flags)) {
  			ret = __group_send_sig_info(sig, info, p);
  			unlock_task_sighand(p, &flags);

  		}

  	}
  
  	return ret;
  }
  
  /*

   * __kill_pgrp_info() sends a signal to a process group: this is what the tty

   * control characters do (^C, ^Z etc)

   * - the caller must hold at least a readlock on tasklist_lock

   */

  int __kill_pgrp_info(int sig, struct siginfo *info, struct pid *pgrp)

  {
  	struct task_struct *p = NULL;
  	int retval, success;

  	success = 0;
  	retval = -ESRCH;

  	do_each_pid_task(pgrp, PIDTYPE_PGID, p) {

  		int err = group_send_sig_info(sig, info, p);
  		success |= !err;
  		retval = err;

  	} while_each_pid_task(pgrp, PIDTYPE_PGID, p);

  	return success ? 0 : retval;
  }

  int kill_pid_info(int sig, struct siginfo *info, struct pid *pid)

  {

  	int error = -ESRCH;

  	struct task_struct *p;

  	rcu_read_lock();

  retry:

  	p = pid_task(pid, PIDTYPE_PID);

  	if (p) {

  		error = group_send_sig_info(sig, info, p);

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

  	rcu_read_unlock();

  	return error;
  }

  int
  kill_proc_info(int sig, struct siginfo *info, pid_t pid)

  {
  	int error;
  	rcu_read_lock();

  	error = kill_pid_info(sig, info, find_vpid(pid));

  	rcu_read_unlock();
  	return error;
  }

  /* like kill_pid_info(), but doesn't use uid/euid of "current" */
  int kill_pid_info_as_uid(int sig, struct siginfo *info, struct pid *pid,

  		      uid_t uid, uid_t euid, u32 secid)

  {
  	int ret = -EINVAL;
  	struct task_struct *p;

  	const struct cred *pcred;

  
  	if (!valid_signal(sig))
  		return ret;
  
  	read_lock(&tasklist_lock);

  	p = pid_task(pid, PIDTYPE_PID);

  	if (!p) {
  		ret = -ESRCH;
  		goto out_unlock;
  	}

  	pcred = __task_cred(p);
  	if ((info == SEND_SIG_NOINFO ||
  	     (!is_si_special(info) && SI_FROMUSER(info))) &&
  	    euid != pcred->suid && euid != pcred->uid &&
  	    uid  != pcred->suid && uid  != pcred->uid) {

  		ret = -EPERM;
  		goto out_unlock;
  	}

  	ret = security_task_kill(p, info, sig, secid);
  	if (ret)
  		goto out_unlock;

  	if (sig && p->sighand) {
  		unsigned long flags;
  		spin_lock_irqsave(&p->sighand->siglock, flags);

  		ret = __send_signal(sig, info, p, 1, 0);

  		spin_unlock_irqrestore(&p->sighand->siglock, flags);
  	}
  out_unlock:
  	read_unlock(&tasklist_lock);
  	return ret;
  }

  EXPORT_SYMBOL_GPL(kill_pid_info_as_uid);

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

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

  {

  	int ret;

  
  	if (pid > 0) {
  		rcu_read_lock();
  		ret = kill_pid_info(sig, info, find_vpid(pid));
  		rcu_read_unlock();
  		return ret;
  	}
  
  	read_lock(&tasklist_lock);
  	if (pid != -1) {
  		ret = __kill_pgrp_info(sig, info,
  				pid ? find_vpid(-pid) : task_pgrp(current));
  	} else {

  		int retval = 0, count = 0;
  		struct task_struct * p;

  		for_each_process(p) {

  			if (task_pid_vnr(p) > 1 &&
  					!same_thread_group(p, current)) {

  				int err = group_send_sig_info(sig, info, p);
  				++count;
  				if (err != -EPERM)
  					retval = err;
  			}
  		}

  		ret = count ? retval : -ESRCH;

  	}

  	read_unlock(&tasklist_lock);

  	return ret;

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

   * The caller must ensure the task can't exit.

   */
  int
  send_sig_info(int sig, struct siginfo *info, struct task_struct *p)
  {
  	int ret;
  	unsigned long flags;
  
  	/*
  	 * 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;

  	spin_lock_irqsave(&p->sighand->siglock, flags);
  	ret = specific_send_sig_info(sig, info, p);
  	spin_unlock_irqrestore(&p->sighand->siglock, flags);

  	return ret;
  }

  #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;
  
  	if ((q = __sigqueue_alloc(current, GFP_KERNEL, 0)))
  		q->flags |= SIGQUEUE_PREALLOC;
  	return(q);
  }
  
  void sigqueue_free(struct sigqueue *q)
  {
  	unsigned long flags;

  	spinlock_t *lock = &current->sighand->siglock;

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

  	 * We must hold ->siglock while testing q->list
  	 * to serialize with collect_signal() or with

  	 * __exit_signal()->flush_sigqueue().

  	 */

  	spin_lock_irqsave(lock, flags);

  	q->flags &= ~SIGQUEUE_PREALLOC;
  	/*
  	 * If it is queued it will be freed when dequeued,
  	 * like the "regular" sigqueue.
  	 */

  	if (!list_empty(&q->list))

  		q = NULL;

  	spin_unlock_irqrestore(lock, flags);

  	if (q)
  		__sigqueue_free(q);

  }

  int send_sigqueue(struct sigqueue *q, struct task_struct *t, int group)

  {

  	int sig = q->info.si_signo;

  	struct sigpending *pending;

  	unsigned long flags;
  	int ret;

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

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

  	ret = 1; /* the signal is ignored */

  	if (!prepare_signal(sig, t, 0))

  		goto out;
  
  	ret = 0;

  	if (unlikely(!list_empty(&q->list))) {
  		/*
  		 * If an SI_TIMER entry is already queue just increment
  		 * the overrun count.
  		 */

  		BUG_ON(q->info.si_code != SI_TIMER);
  		q->info.si_overrun++;

  		goto out;

  	}

  	q->info.si_overrun = 0;

  	signalfd_notify(t, sig);

  	pending = group ? &t->signal->shared_pending : &t->pending;

  	list_add_tail(&q->list, &pending->list);
  	sigaddset(&pending->signal, sig);

  	complete_signal(sig, t, group);

  out:
  	unlock_task_sighand(t, &flags);
  ret:
  	return ret;

  }

  /*
   * Wake up any threads in the parent blocked in wait* syscalls.
   */
  static inline void __wake_up_parent(struct task_struct *p,
  				    struct task_struct *parent)
  {
  	wake_up_interruptible_sync(&parent->signal->wait_chldexit);
  }
  
  /*
   * Let a parent know about the death of a child.
   * For a stopped/continued status change, use do_notify_parent_cldstop instead.

   *
   * Returns -1 if our parent ignored us and so we've switched to
   * self-reaping, or else @sig.

   */

  int do_notify_parent(struct task_struct *tsk, int sig)

  {
  	struct siginfo info;
  	unsigned long flags;
  	struct sighand_struct *psig;

  	int ret = sig;

  
  	BUG_ON(sig == -1);
  
   	/* do_notify_parent_cldstop should have been called instead.  */

   	BUG_ON(task_is_stopped_or_traced(tsk));

  
  	BUG_ON(!tsk->ptrace &&
  	       (tsk->group_leader != tsk || !thread_group_empty(tsk)));
  
  	info.si_signo = sig;
  	info.si_errno = 0;

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

  	info.si_uid = __task_cred(tsk)->uid;

  	rcu_read_unlock();

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

  
  	info.si_status = tsk->exit_code & 0x7f;
  	if (tsk->exit_code & 0x80)
  		info.si_code = CLD_DUMPED;
  	else if (tsk->exit_code & 0x7f)
  		info.si_code = CLD_KILLED;
  	else {
  		info.si_code = CLD_EXITED;
  		info.si_status = tsk->exit_code >> 8;
  	}
  
  	psig = tsk->parent->sighand;
  	spin_lock_irqsave(&psig->siglock, flags);

  	if (!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).
  		 */

  		ret = tsk->exit_signal = -1;

  		if (psig->action[SIGCHLD-1].sa.sa_handler == SIG_IGN)

  			sig = -1;

  	}

  	if (valid_signal(sig) && sig > 0)

  		__group_send_sig_info(sig, &info, tsk->parent);
  	__wake_up_parent(tsk, tsk->parent);
  	spin_unlock_irqrestore(&psig->siglock, flags);

  	return ret;

  }

  static void do_notify_parent_cldstop(struct task_struct *tsk, int why)

  {
  	struct siginfo info;
  	unsigned long flags;

  	struct task_struct *parent;

  	struct sighand_struct *sighand;

  	if (tsk->ptrace & PT_PTRACED)

  		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() abot the following 3 lines
  	 */
  	rcu_read_lock();
  	info.si_pid = task_pid_nr_ns(tsk, tsk->parent->nsproxy->pid_ns);

  	info.si_uid = __task_cred(tsk)->uid;

  	rcu_read_unlock();

  	info.si_utime = cputime_to_clock_t(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 & PT_PTRACED))
  		return 0;

  	/*
  	 * Are we in the middle of do_coredump?
  	 * If so and our tracer is also part of the coredump stopping
  	 * is a deadlock situation, and pointless because our tracer
  	 * is dead so don't allow us to stop.
  	 * If SIGKILL was already sent before the caller unlocked

  	 * ->siglock we must see ->core_state != NULL. Otherwise it

  	 * is safe to enter schedule().
  	 */

  	if (unlikely(current->mm->core_state) &&

  	    unlikely(current->mm == current->parent->mm))
  		return 0;
  
  	return 1;
  }

  /*

   * Return nonzero if there is a SIGKILL that should be waking us up.
   * Called with the siglock held.
   */
  static int sigkill_pending(struct task_struct *tsk)
  {

  	return	sigismember(&tsk->pending.signal, SIGKILL) ||
  		sigismember(&tsk->signal->shared_pending.signal, SIGKILL);

  }
  
  /*

   * This must be called with current->sighand->siglock held.
   *
   * This should be the path for all ptrace stops.
   * We always set current->last_siginfo while stopped here.
   * That makes it a way to test a stopped process for
   * being ptrace-stopped vs being job-control-stopped.
   *

   * If we actually decide not to stop at all because the tracer
   * is gone, we keep current->exit_code unless clear_code.

   */

  static void ptrace_stop(int exit_code, int clear_code, siginfo_t *info)

  {

  	if (arch_ptrace_stop_needed(exit_code, info)) {
  		/*
  		 * The arch code has something special to do before a
  		 * ptrace stop.  This is allowed to block, e.g. for faults
  		 * on user stack pages.  We can't keep the siglock while
  		 * calling arch_ptrace_stop, so we must release it now.
  		 * To preserve proper semantics, we must do this before
  		 * any signal bookkeeping like checking group_stop_count.
  		 * Meanwhile, a SIGKILL could come in before we retake the
  		 * siglock.  That must prevent us from sleeping in TASK_TRACED.
  		 * So after regaining the lock, we must check for SIGKILL.
  		 */
  		spin_unlock_irq(&current->sighand->siglock);
  		arch_ptrace_stop(exit_code, info);
  		spin_lock_irq(&current->sighand->siglock);

  		if (sigkill_pending(current))
  			return;

  	}

  	/*
  	 * If there is a group stop in progress,
  	 * we must participate in the bookkeeping.
  	 */
  	if (current->signal->group_stop_count > 0)
  		--current->signal->group_stop_count;
  
  	current->last_siginfo = info;
  	current->exit_code = exit_code;
  
  	/* Let the debugger run.  */

  	__set_current_state(TASK_TRACED);

  	spin_unlock_irq(&current->sighand->siglock);
  	read_lock(&tasklist_lock);

  	if (may_ptrace_stop()) {

  		do_notify_parent_cldstop(current, CLD_TRAPPED);

  		/*
  		 * Don't want to allow preemption here, because
  		 * sys_ptrace() needs this task to be inactive.
  		 *
  		 * XXX: implement read_unlock_no_resched().
  		 */
  		preempt_disable();

  		read_unlock(&tasklist_lock);

  		preempt_enable_no_resched();

  		schedule();
  	} else {
  		/*
  		 * By the time we got the lock, our tracer went away.

  		 * Don't drop the lock yet, another tracer may come.

  		 */

  		__set_current_state(TASK_RUNNING);

  		if (clear_code)
  			current->exit_code = 0;

  		read_unlock(&tasklist_lock);

  	}
  
  	/*

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

  	 * We are back.  Now reacquire the siglock before touching
  	 * last_siginfo, so that we are sure to have synchronized with
  	 * any signal-sending on another CPU that wants to examine it.
  	 */
  	spin_lock_irq(&current->sighand->siglock);
  	current->last_siginfo = NULL;
  
  	/*
  	 * Queued signals ignored us while we were stopped for tracing.
  	 * So check for any that we should take before resuming user mode.

  	 * This sets TIF_SIGPENDING, but never clears it.

  	 */

  	recalc_sigpending_tsk(current);

  }
  
  void ptrace_notify(int exit_code)
  {
  	siginfo_t info;
  
  	BUG_ON((exit_code & (0x7f | ~0xffff)) != SIGTRAP);
  
  	memset(&info, 0, sizeof info);
  	info.si_signo = SIGTRAP;
  	info.si_code = exit_code;

  	info.si_pid = task_pid_vnr(current);

  	info.si_uid = current_uid();

  
  	/* Let the debugger run.  */
  	spin_lock_irq(&current->sighand->siglock);

  	ptrace_stop(exit_code, 1, &info);

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

  static void
  finish_stop(int stop_count)
  {
  	/*
  	 * If there are no other threads in the group, or if there is
  	 * a group stop in progress and we are the last to stop,
  	 * report to the parent.  When ptraced, every thread reports itself.
  	 */

  	if (tracehook_notify_jctl(stop_count == 0, CLD_STOPPED)) {

  		read_lock(&tasklist_lock);
  		do_notify_parent_cldstop(current, CLD_STOPPED);
  		read_unlock(&tasklist_lock);
  	}

  	do {
  		schedule();
  	} while (try_to_freeze());

  	/*
  	 * Now we don't run again until continued.
  	 */
  	current->exit_code = 0;
  }
  
  /*
   * This performs the stopping for SIGSTOP and other stop signals.
   * We have to stop all threads in the thread group.
   * Returns nonzero if we've actually stopped and released the siglock.
   * Returns zero if we didn't stop and still hold the siglock.
   */

  static int do_signal_stop(int signr)

  {
  	struct signal_struct *sig = current->signal;

  	int stop_count;

  	if (sig->group_stop_count > 0) {
  		/*
  		 * There is a group stop in progress.  We don't need to
  		 * start another one.
  		 */

  		stop_count = --sig->group_stop_count;

  	} else {

  		struct task_struct *t;

  		if (!likely(sig->flags & SIGNAL_STOP_DEQUEUED) ||

  		    unlikely(signal_group_exit(sig)))

  			return 0;

  		/*
  		 * There is no group stop already in progress.

  		 * We must initiate one now.

  		 */

  		sig->group_exit_code = signr;

  		stop_count = 0;
  		for (t = next_thread(current); t != current; t = next_thread(t))

  			/*

  			 * Setting state to TASK_STOPPED for a group
  			 * stop is always done with the siglock held,
  			 * so this check has no races.

  			 */

  			if (!(t->flags & PF_EXITING) &&

  			    !task_is_stopped_or_traced(t)) {

  				stop_count++;
  				signal_wake_up(t, 0);
  			}
  		sig->group_stop_count = stop_count;

  	}

  	if (stop_count == 0)
  		sig->flags = SIGNAL_STOP_STOPPED;
  	current->exit_code = sig->group_exit_code;
  	__set_current_state(TASK_STOPPED);
  
  	spin_unlock_irq(&current->sighand->siglock);

  	finish_stop(stop_count);
  	return 1;
  }

  static int ptrace_signal(int signr, siginfo_t *info,
  			 struct pt_regs *regs, void *cookie)
  {
  	if (!(current->ptrace & PT_PTRACED))
  		return signr;
  
  	ptrace_signal_deliver(regs, cookie);
  
  	/* Let the debugger run.  */
  	ptrace_stop(signr, 0, info);
  
  	/* We're back.  Did the debugger cancel the sig?  */
  	signr = current->exit_code;
  	if (signr == 0)
  		return signr;
  
  	current->exit_code = 0;
  
  	/* Update the siginfo structure if the signal has
  	   changed.  If the debugger wanted something
  	   specific in the siginfo structure then it should
  	   have updated *info via PTRACE_SETSIGINFO.  */
  	if (signr != info->si_signo) {
  		info->si_signo = signr;
  		info->si_errno = 0;
  		info->si_code = SI_USER;
  		info->si_pid = task_pid_vnr(current->parent);

  		info->si_uid = task_uid(current->parent);

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

  int get_signal_to_deliver(siginfo_t *info, struct k_sigaction *return_ka,
  			  struct pt_regs *regs, void *cookie)
  {

  	struct sighand_struct *sighand = current->sighand;
  	struct signal_struct *signal = current->signal;
  	int signr;

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

  	try_to_freeze();

  	spin_lock_irq(&sighand->siglock);

  	/*
  	 * Every stopped thread goes here after wakeup. Check to see if
  	 * we should notify the parent, prepare_signal(SIGCONT) encodes
  	 * the CLD_ si_code into SIGNAL_CLD_MASK bits.
  	 */

  	if (unlikely(signal->flags & SIGNAL_CLD_MASK)) {
  		int why = (signal->flags & SIGNAL_STOP_CONTINUED)

  				? CLD_CONTINUED : CLD_STOPPED;

  		signal->flags &= ~SIGNAL_CLD_MASK;
  		spin_unlock_irq(&sighand->siglock);

  		if (unlikely(!tracehook_notify_jctl(1, why)))
  			goto relock;

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

  	for (;;) {
  		struct k_sigaction *ka;

  		if (unlikely(signal->group_stop_count > 0) &&

  		    do_signal_stop(0))

  			goto relock;

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

  			if (!signr)

  				break; /* will return 0 */
  
  			if (signr != SIGKILL) {
  				signr = ptrace_signal(signr, info,
  						      regs, cookie);
  				if (!signr)
  					continue;
  			}
  
  			ka = &sighand->action[signr-1];

  		}

  		if (ka->sa.sa_handler == SIG_IGN) /* Do nothing.  */
  			continue;
  		if (ka->sa.sa_handler != SIG_DFL) {
  			/* Run the handler.  */
  			*return_ka = *ka;
  
  			if (ka->sa.sa_flags & SA_ONESHOT)
  				ka->sa.sa_handler = SIG_DFL;
  
  			break; /* will return non-zero "signr" value */
  		}
  
  		/*
  		 * Now we are doing the default action for this signal.
  		 */
  		if (sig_kernel_ignore(signr)) /* Default is nothing. */
  			continue;

  		/*

  		 * Global init gets no signals it doesn't want.

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

  		 */

  		if (unlikely(signal->flags & SIGNAL_UNKILLABLE) &&

  				!sig_kernel_only(signr))

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

  				spin_unlock_irq(&sighand->siglock);

  
  				/* signals can be posted during this window */

  				if (is_current_pgrp_orphaned())

  					goto relock;

  				spin_lock_irq(&sighand->siglock);

  			}

  			if (likely(do_signal_stop(info->si_signo))) {

  				/* It released the siglock.  */
  				goto relock;
  			}
  
  			/*
  			 * We didn't actually stop, due to a race
  			 * with SIGCONT or something like that.
  			 */
  			continue;
  		}

  		spin_unlock_irq(&sighand->siglock);

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

  		if (sig_kernel_coredump(signr)) {

  			if (print_fatal_signals)

  				print_fatal_signal(regs, info->si_signo);

  			/*
  			 * If it was able to dump core, this kills all
  			 * other threads in the group and synchronizes with
  			 * their demise.  If we lost the race with another
  			 * thread getting here, it set group_exit_code
  			 * first and our do_group_exit call below will use
  			 * that value and ignore the one we pass it.
  			 */

  			do_coredump(info->si_signo, info->si_signo, regs);

  		}
  
  		/*
  		 * Death signals, no core dump.
  		 */

  		do_group_exit(info->si_signo);

  		/* NOTREACHED */
  	}

  	spin_unlock_irq(&sighand->siglock);

  	return signr;
  }

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

  	struct task_struct *t;

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

  	}

  	spin_lock_irq(&tsk->sighand->siglock);

  	/*
  	 * From now this task is not visible for group-wide signals,
  	 * see wants_signal(), do_signal_stop().
  	 */
  	tsk->flags |= PF_EXITING;

  	if (!signal_pending(tsk))
  		goto out;
  
  	/* It could be that __group_complete_signal() choose us to
  	 * notify about group-wide signal. Another thread should be
  	 * woken now to take the signal since we will not.
  	 */
  	for (t = tsk; (t = next_thread(t)) != tsk; )
  		if (!signal_pending(t) && !(t->flags & PF_EXITING))
  			recalc_sigpending_and_wake(t);
  
  	if (unlikely(tsk->signal->group_stop_count) &&
  			!--tsk->signal->group_stop_count) {
  		tsk->signal->flags = SIGNAL_STOP_STOPPED;
  		group_stop = 1;
  	}
  out:

  	spin_unlock_irq(&tsk->sighand->siglock);

  	if (unlikely(group_stop) && tracehook_notify_jctl(1, CLD_STOPPED)) {

  		read_lock(&tasklist_lock);
  		do_notify_parent_cldstop(tsk, CLD_STOPPED);
  		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.
   */

  SYSCALL_DEFINE0(restart_syscall)

  {
  	struct restart_block *restart = &current_thread_info()->restart_block;
  	return restart->fn(restart);
  }
  
  long do_no_restart_syscall(struct restart_block *param)
  {
  	return -EINTR;
  }
  
  /*
   * We don't need to get the kernel lock - this is all local to this
   * particular thread.. (and that's good, because this is _heavily_
   * used by various programs)
   */
  
  /*
   * This is also useful for kernel threads that want to temporarily
   * (or permanently) block certain signals.
   *
   * NOTE! Unlike the user-mode sys_sigprocmask(), the kernel
   * interface happily blocks "unblockable" signals like SIGKILL
   * and friends.
   */
  int sigprocmask(int how, sigset_t *set, sigset_t *oldset)
  {
  	int error;

  
  	spin_lock_irq(&current->sighand->siglock);

  	if (oldset)
  		*oldset = current->blocked;

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

  	return error;
  }

  SYSCALL_DEFINE4(rt_sigprocmask, int, how, sigset_t __user *, set,
  		sigset_t __user *, oset, size_t, sigsetsize)

  {
  	int error = -EINVAL;
  	sigset_t old_set, new_set;
  
  	/* XXX: Don't preclude handling different sized sigset_t's.  */
  	if (sigsetsize != sizeof(sigset_t))
  		goto out;
  
  	if (set) {
  		error = -EFAULT;
  		if (copy_from_user(&new_set, set, sizeof(*set)))
  			goto out;
  		sigdelsetmask(&new_set, sigmask(SIGKILL)|sigmask(SIGSTOP));
  
  		error = sigprocmask(how, &new_set, &old_set);
  		if (error)
  			goto out;
  		if (oset)
  			goto set_old;
  	} else if (oset) {
  		spin_lock_irq(&current->sighand->siglock);
  		old_set = current->blocked;
  		spin_unlock_irq(&current->sighand->siglock);
  
  	set_old:
  		error = -EFAULT;
  		if (copy_to_user(oset, &old_set, sizeof(*oset)))
  			goto out;
  	}
  	error = 0;
  out:
  	return error;
  }
  
  long do_sigpending(void __user *set, unsigned long sigsetsize)
  {
  	long error = -EINVAL;
  	sigset_t pending;
  
  	if (sigsetsize > sizeof(sigset_t))
  		goto out;
  
  	spin_lock_irq(&current->sighand->siglock);
  	sigorsets(&pending, &current->pending.signal,
  		  &current->signal->shared_pending.signal);
  	spin_unlock_irq(&current->sighand->siglock);
  
  	/* Outside the lock because only this thread touches it.  */
  	sigandsets(&pending, &current->blocked, &pending);
  
  	error = -EFAULT;
  	if (!copy_to_user(set, &pending, sigsetsize))
  		error = 0;
  
  out:
  	return error;
  }	

  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
  		break;
  	case __SI_CHLD:
  		err |= __put_user(from->si_pid, &to->si_pid);
  		err |= __put_user(from->si_uid, &to->si_uid);
  		err |= __put_user(from->si_status, &to->si_status);
  		err |= __put_user(from->si_utime, &to->si_utime);
  		err |= __put_user(from->si_stime, &to->si_stime);
  		break;
  	case __SI_RT: /* This is not generated by the kernel as of now. */
  	case __SI_MESGQ: /* But this is */
  		err |= __put_user(from->si_pid, &to->si_pid);
  		err |= __put_user(from->si_uid, &to->si_uid);
  		err |= __put_user(from->si_ptr, &to->si_ptr);
  		break;
  	default: /* this is just in case for now ... */
  		err |= __put_user(from->si_pid, &to->si_pid);
  		err |= __put_user(from->si_uid, &to->si_uid);
  		break;
  	}
  	return err;
  }
  
  #endif

  SYSCALL_DEFINE4(rt_sigtimedwait, const sigset_t __user *, uthese,
  		siginfo_t __user *, uinfo, const struct timespec __user *, uts,
  		size_t, sigsetsize)

  {
  	int ret, sig;
  	sigset_t these;
  	struct timespec ts;
  	siginfo_t info;
  	long timeout = 0;
  
  	/* XXX: Don't preclude handling different sized sigset_t's.  */
  	if (sigsetsize != sizeof(sigset_t))
  		return -EINVAL;
  
  	if (copy_from_user(&these, uthese, sizeof(these)))
  		return -EFAULT;
  		
  	/*
  	 * Invert the set of allowed signals to get those we
  	 * want to block.
  	 */
  	sigdelsetmask(&these, sigmask(SIGKILL)|sigmask(SIGSTOP));
  	signotset(&these);
  
  	if (uts) {
  		if (copy_from_user(&ts, uts, sizeof(ts)))
  			return -EFAULT;
  		if (ts.tv_nsec >= 1000000000L || ts.tv_nsec < 0
  		    || ts.tv_sec < 0)
  			return -EINVAL;
  	}
  
  	spin_lock_irq(&current->sighand->siglock);
  	sig = dequeue_signal(current, &these, &info);
  	if (!sig) {
  		timeout = MAX_SCHEDULE_TIMEOUT;
  		if (uts)
  			timeout = (timespec_to_jiffies(&ts)
  				   + (ts.tv_sec || ts.tv_nsec));
  
  		if (timeout) {
  			/* None ready -- temporarily unblock those we're
  			 * interested while we are sleeping in so that we'll
  			 * be awakened when they arrive.  */
  			current->real_blocked = current->blocked;
  			sigandsets(&current->blocked, &current->blocked, &these);
  			recalc_sigpending();
  			spin_unlock_irq(&current->sighand->siglock);

  			timeout = schedule_timeout_interruptible(timeout);

  			spin_lock_irq(&current->sighand->siglock);
  			sig = dequeue_signal(current, &these, &info);
  			current->blocked = current->real_blocked;
  			siginitset(&current->real_blocked, 0);
  			recalc_sigpending();
  		}
  	}
  	spin_unlock_irq(&current->sighand->siglock);
  
  	if (sig) {
  		ret = sig;
  		if (uinfo) {
  			if (copy_siginfo_to_user(uinfo, &info))
  				ret = -EFAULT;
  		}
  	} else {
  		ret = -EAGAIN;
  		if (timeout)
  			ret = -EINTR;
  	}
  
  	return ret;
  }

  SYSCALL_DEFINE2(kill, pid_t, pid, int, sig)

  {
  	struct siginfo info;
  
  	info.si_signo = sig;
  	info.si_errno = 0;
  	info.si_code = SI_USER;

  	info.si_pid = task_tgid_vnr(current);

  	info.si_uid = current_uid();

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

  static int do_tkill(pid_t tgid, pid_t pid, int sig)

  {

  	int error;

  	struct siginfo info;

  	struct task_struct *p;

  	unsigned long flags;

  	error = -ESRCH;

  	info.si_signo = sig;
  	info.si_errno = 0;
  	info.si_code = SI_TKILL;

  	info.si_pid = task_tgid_vnr(current);

  	info.si_uid = current_uid();

  	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 lock_task_sighand() fails we pretend the task dies
  		 * after receiving the signal. The window is tiny, and the
  		 * signal is private anyway.

  		 */

  		if (!error && sig && lock_task_sighand(p, &flags)) {

  			error = specific_send_sig_info(sig, &info, p);

  			unlock_task_sighand(p, &flags);

  		}
  	}

  	rcu_read_unlock();

  	return error;
  }

  /**
   *  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);
  }

  /*
   *  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);

  }

  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(), which adds source info.  */
  	if (info.si_code >= 0)
  		return -EPERM;
  	info.si_signo = sig;
  
  	/* POSIX.1b doesn't mention process groups.  */
  	return kill_proc_info(sig, &info, pid);
  }

  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) {