[PATCH v2 1/3] signal: change sig_task_ignored(force) to take sig_kernel_only() into account

[Oleg Nesterov <oleg@redhat.com>]

sig_task_ignored(force => true) returns false unless sig_kernel_ignore().
This makes no sense if !sig_kernel_only(), the signal will be dropped in
get_signal() anyway.

This patch simplifies the next change and allows us to do more cleanups,
in particular we can unify the SIGNAL_UNKILLABLE/sig_kernel_only() check
in sig_task_ignored() and get_signal().

The user-visible change is that, since we drop the SIG_DFL signal early,
it won't be reported to debugger. I think this is fine, but probably we
will change this later, we need to fix this logic anyway. Currently we
rely on the fact that (say) send_sigtrap() uses force_sig_info() which
clears SIGNAL_UNKILLABLE, and this is really bad.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 kernel/signal.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index d64efad..87209e5 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -72,7 +72,7 @@ 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);
-- 
1.5.5.1