kernel/signal.c: protect the SIGNAL_UNKILLABLE tasks from !sig_kernel…

…_only() signals

Change sig_task_ignored() to drop the SIG_DFL && !sig_kernel_only()
signals even if force == T.  This simplifies the next change and this
matches the same check in get_signal() which will drop these signals
anyway.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Oleg Nesterov <[email protected]>
Tested-by: Kyle Huey <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

kernel/signal.c

@@ -78,7 +78,7 @@ static int sig_task_ignored(struct task_struct *t, int sig, bool force)
 	handler = sig_handler(t, sig);
 
 	if (unlikely(t->signal->flags & SIGNAL_UNKILLABLE) &&
-			handler == SIG_DFL && !force)
+	    handler == SIG_DFL && !(force && sig_kernel_only(sig)))
 		return 1;
 
 	return sig_handler_ignored(handler, sig);