signal: make unhandled_signal() return bool

unhandled_signal() already behaves like a boolean function.  Let's
actually declare it as such too.  All callers treat it as such too.

Link: http://lkml.kernel.org/r/20180602103653.18181-13-christian@brauner.io
Signed-off-by: Christian Brauner <christian@brauner.io>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: James Morris <james.morris@microsoft.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/signal.h

@@ -287,7 +287,7 @@ static inline void disallow_signal(int sig)
 
 extern struct kmem_cache *sighand_cachep;
 
-int unhandled_signal(struct task_struct *tsk, int sig);
+extern bool unhandled_signal(struct task_struct *tsk, int sig);
 
 /*
  * In POSIX a signal is sent either to a specific thread (Linux task)

kernel/signal.c

@@ -505,13 +505,15 @@ flush_signal_handlers(struct task_struct *t, int force_default)
 	}
 }
 
-int unhandled_signal(struct task_struct *tsk, int sig)
+bool 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;
+		return true;
+
 	if (handler != SIG_IGN && handler != SIG_DFL)
-		return 0;
+		return false;
+
 	/* if ptraced, let the tracer determine */
 	return !tsk->ptrace;
 }