/*
   *  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>

  #include <linux/cn_proc.h>

  #include <linux/compiler.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;

  	pr_info("%s/%d: reached RLIMIT_SIGPENDING, dropped signal %d
  ",

  				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 long 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;

  		smp_mb();	/* advised by wake_up_bit() */

  		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 long 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 this kthread.

   */

  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;

  #ifdef __ARCH_HAS_SA_RESTORER

  		ka->sa.sa_restorer = NULL;
  #endif

  		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;

  }

  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)

  		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.

   */

  static int flush_sigqueue_mask(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;
  }

  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 bool prepare_signal(int sig, struct task_struct *p, bool force)

  {

  	struct signal_struct *signal = p->signal;

  	struct task_struct *t;

  	sigset_t flush;

  	if (signal->flags & (SIGNAL_GROUP_EXIT | SIGNAL_GROUP_COREDUMP)) {

  		if (!(signal->flags & SIGNAL_GROUP_EXIT))

  			return sig == SIGKILL;

  		/*

  		 * 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.
  		 */

  		siginitset(&flush, sigmask(SIGCONT));

  		flush_sigqueue_mask(&flush, &signal->shared_pending);

  		for_each_thread(p, t)

  			flush_sigqueue_mask(&flush, &t->pending);

  	} else if (sig == SIGCONT) {

  		unsigned int why;

  		/*

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

  		 */

  		siginitset(&flush, SIG_KERNEL_STOP_MASK);

  		flush_sigqueue_mask(&flush, &signal->shared_pending);

  		for_each_thread(p, t) {

  			flush_sigqueue_mask(&flush, &t->pending);

  			task_clear_jobctl_pending(t, JOBCTL_STOP_PENDING);

  			if (likely(!(t->ptrace & PT_SEIZED)))
  				wake_up_state(t, __TASK_STOPPED);
  			else
  				ptrace_trap_notify(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();

  	pr_info("potentially unexpected fatal signal %d.
  ", signr);

  #if defined(__i386__) && !defined(__arch_um__)

  	pr_info("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;

  			pr_cont("%02x ", insn);

  		}
  	}

  	pr_cont("
  ");

  #endif

  	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 (;;) {

  		/*
  		 * Disable interrupts early to avoid deadlocks.
  		 * See rcu_read_unlock() comment header for details.
  		 */

  		local_irq_save(*flags);
  		rcu_read_lock();

  		sighand = rcu_dereference(tsk->sighand);

  		if (unlikely(sighand == NULL)) {
  			rcu_read_unlock();
  			local_irq_restore(*flags);

  			break;

  		}

  		/*
  		 * This sighand can be already freed and even reused, but
  		 * we rely on SLAB_DESTROY_BY_RCU and sighand_ctor() which
  		 * initializes ->siglock: this slab can't go away, it has
  		 * the same object type, ->siglock can't be reinitialized.
  		 *
  		 * We need to ensure that tsk->sighand is still the same
  		 * after we take the lock, we can race with de_thread() or
  		 * __exit_signal(). In the latter case the next iteration
  		 * must see ->sighand == NULL.
  		 */

  		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;

  	for (;;) {
  		rcu_read_lock();
  		p = pid_task(pid, PIDTYPE_PID);
  		if (p)
  			error = group_send_sig_info(sig, info, p);
  		rcu_read_unlock();
  		if (likely(!p || error != -ESRCH))
  			return error;

  		/*
  		 * 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.
  		 */
  	}

  }

  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;

  	cputime_t utime, stime;

  
  	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();

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

  	cputime_t utime, stime;

  	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();

  	task_cputime(tsk, &utime, &stime);
  	info.si_utime = cputime_to_clock_t(utime);
  	info.si_stime = cputime_to_clock_t(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.

   */