signal: fix __send_signal() false positive kmemcheck warning

This false positive is due to field padding in struct sigqueue. When
this dynamically allocated structure is copied to the stack (in arch-
specific delivery code), kmemcheck sees a read from the padding, which
is, naturally, uninitialized.

Hide the false positive using the __GFP_NOTRACK_FALSE_POSITIVE flag.
Also made the rlimit override code a bit clearer by introducing a new
variable.

Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Vegard Nossum <vegard.nossum@gmail.com>

kernel/signal.c

@@ -832,6 +832,7 @@ static int __send_signal(int sig, struct siginfo *info, struct task_struct *t,
 {
 	struct sigpending *pending;
 	struct sigqueue *q;
+	int override_rlimit;
 
 	trace_sched_signal_send(sig, t);
 
@@ -863,9 +864,13 @@ static int __send_signal(int sig, struct siginfo *info, struct task_struct *t,
 	   make sure at least one signal gets delivered and don't
 	   pass on the info struct.  */
 
-	q = __sigqueue_alloc(t, GFP_ATOMIC, (sig < SIGRTMIN &&
-					     (is_si_special(info) ||
-					      info->si_code >= 0)));
+	if (sig < SIGRTMIN)
+		override_rlimit = (is_si_special(info) || info->si_code >= 0);
+	else
+		override_rlimit = 0;
+
+	q = __sigqueue_alloc(t, GFP_ATOMIC | __GFP_NOTRACK_FALSE_POSITIVE,
+		override_rlimit);
 	if (q) {
 		list_add_tail(&q->list, &pending->list);
 		switch ((unsigned long) info) {