signals: disallow_signal() should flush the potentially pending signal

disallow_signal() simply sets SIG_IGN, this is not enough and
recalc_sigpending() is simply pointless because in can never change the
state of TIF_SIGPENDING.

If we ignore a signal, we also need to do flush_sigqueue_mask() for the
case when this signal is pending, this way recalc_sigpending() can
actually clear TIF_SIGPENDING and we do not "leak" the allocated
siginfo's.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/signal.c

@@ -3085,8 +3085,15 @@ EXPORT_SYMBOL(allow_signal);
 
 void disallow_signal(int sig)
 {
+	sigset_t mask;
+
+	sigemptyset(&mask);
+	sigaddset(&mask, sig);
+
 	spin_lock_irq(&current->sighand->siglock);
 	current->sighand->action[(sig)-1].sa.sa_handler = SIG_IGN;
+	flush_sigqueue_mask(&mask, &current->signal->shared_pending);
+	flush_sigqueue_mask(&mask, &current->pending);
 	recalc_sigpending();
 	spin_unlock_irq(&current->sighand->siglock);
 }