signals: fold sig_ignored() into handle_stop_signal()

Rename handle_stop_signal() to prepare_signal(), make it return a boolean, and
move the callsites of sig_ignored() into it.

No functional changes for now.  But it would be nice to factor out the "should
we drop this signal" checks as much as possible, before we try to fix the bugs
with the sub-namespace init's signals (actually the global /sbin/init has some
problems with signals too).

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/signal.c

@@ -558,24 +558,25 @@ static int check_kill_permission(int sig, struct siginfo *info,
 static void do_notify_parent_cldstop(struct task_struct *tsk, int why);
 
 /*
- * Handle magic process-wide effects of stop/continue signals.
- * Unlike the signal actions, these happen immediately at signal-generation
+ * 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.
+ * 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 void handle_stop_signal(int sig, struct task_struct *p)
+static int prepare_signal(int sig, struct task_struct *p)
 {
 	struct signal_struct *signal = p->signal;
 	struct task_struct *t;
 
-	if (signal->flags & SIGNAL_GROUP_EXIT)
+	if (unlikely(signal->flags & SIGNAL_GROUP_EXIT)) {
 		/*
-		 * The process is in the middle of dying already.
+		 * The process is in the middle of dying, nothing to do.
 		 */
-		return;
-
-	if (sig_kernel_stop(sig)) {
+	} else if (sig_kernel_stop(sig)) {
 		/*
 		 * This is a stop signal.  Remove SIGCONT from all queues.
 		 */
@@ -644,6 +645,8 @@ static void handle_stop_signal(int sig, struct task_struct *p)
 			signal->flags &= ~SIGNAL_STOP_DEQUEUED;
 		}
 	}
+
+	return !sig_ignored(p, sig);
 }
 
 /*
@@ -753,15 +756,16 @@ static int send_signal(int sig, struct siginfo *info, struct task_struct *t,
 	struct sigqueue *q;
 
 	assert_spin_locked(&t->sighand->siglock);
-	handle_stop_signal(sig, t);
+	if (!prepare_signal(sig, t))
+		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 (sig_ignored(t, sig) || legacy_queue(pending, sig))
+	if (legacy_queue(pending, sig))
 		return 0;
 
 	/*
@@ -1247,10 +1251,8 @@ int send_sigqueue(struct sigqueue *q, struct task_struct *t, int group)
 	if (!likely(lock_task_sighand(t, &flags)))
 		goto ret;
 
-	handle_stop_signal(sig, t);
-
-	ret = 1;
-	if (sig_ignored(t, sig))
+	ret = 1; /* the signal is ignored */
+	if (!prepare_signal(sig, t))
 		goto out;
 
 	ret = 0;