tracehook: tracehook_consider_fatal_signal

This defines tracehook_consider_fatal_signal() has a fine-grained hook for
deciding to skip the special cases for a fatal signal, as ptrace does.
There is no change, only cleanup.
Signed-off-by: NRoland McGrath <roland@redhat.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Reviewed-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

include/linux/tracehook.h

@@ -331,4 +331,25 @@ static inline int tracehook_consider_ignored_signal(struct task_struct *task,
 	return (task_ptrace(task) & PT_PTRACED) != 0;
 }
 
+/**
+ * tracehook_consider_fatal_signal - suppress special handling of fatal signal
+ * @task:		task receiving the signal
+ * @sig:		signal number being sent
+ * @handler:		%SIG_DFL or %SIG_IGN
+ *
+ * Return nonzero to prevent special handling of this termination signal.
+ * Normally @handler is %SIG_DFL.  It can be %SIG_IGN if @sig is ignored,
+ * in which case force_sig() is about to reset it to %SIG_DFL.
+ * When this returns zero, this signal might cause a quick termination
+ * that does not give the debugger a chance to intercept the signal.
+ *
+ * Called with or without @task->sighand->siglock held.
+ */
+static inline int tracehook_consider_fatal_signal(struct task_struct *task,
+						  int sig,
+						  void __user *handler)
+{
+	return (task_ptrace(task) & PT_PTRACED) != 0;
+}
+
 #endif	/* <linux/tracehook.h> */

kernel/signal.c

@@ -300,12 +300,12 @@ flush_signal_handlers(struct task_struct *t, int force_default)
 
 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 (tsk->ptrace & PT_PTRACED)
+	if (handler != SIG_IGN && handler != SIG_DFL)
 		return 0;
-	return (tsk->sighand->action[sig-1].sa.sa_handler == SIG_IGN) ||
-		(tsk->sighand->action[sig-1].sa.sa_handler == SIG_DFL);
+	return !tracehook_consider_fatal_signal(tsk, sig, handler);
 }
 
 
@@ -761,7 +761,8 @@ static void complete_signal(int sig, struct task_struct *p, int group)
 	if (sig_fatal(p, sig) &&
 	    !(signal->flags & (SIGNAL_UNKILLABLE | SIGNAL_GROUP_EXIT)) &&
 	    !sigismember(&t->real_blocked, sig) &&
-	    (sig == SIGKILL || !(t->ptrace & PT_PTRACED))) {
+	    (sig == SIGKILL ||
+	     !tracehook_consider_fatal_signal(t, sig, SIG_DFL))) {
 		/*
 		 * This signal will be fatal to the whole group.
 		 */