tick: Use zalloc_cpumask_var for allocating offstack cpumasks

commit b352bc1c (tick: Convert broadcast cpu bitmaps to
cpumask_var_t) broke CONFIG_CPUMASK_OFFSTACK in a very subtle way.

Instead of allocating the cpumasks with zalloc_cpumask_var it uses
alloc_cpumask_var, so we can get random data there, which of course
confuses the logic completely and causes random failures.
Reported-and-tested-by: Dave Jones <davej@redhat.com>
Reported-and-tested-by: Yinghai Lu <yinghai@kernel.org>
Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1305032015060.2990@ionosSigned-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/time/tick-broadcast.c

@@ -785,11 +785,11 @@ bool tick_broadcast_oneshot_available(void)
 
 void __init tick_broadcast_init(void)
 {
-	alloc_cpumask_var(&tick_broadcast_mask, GFP_NOWAIT);
-	alloc_cpumask_var(&tmpmask, GFP_NOWAIT);
+	zalloc_cpumask_var(&tick_broadcast_mask, GFP_NOWAIT);
+	zalloc_cpumask_var(&tmpmask, GFP_NOWAIT);
 #ifdef CONFIG_TICK_ONESHOT
-	alloc_cpumask_var(&tick_broadcast_oneshot_mask, GFP_NOWAIT);
-	alloc_cpumask_var(&tick_broadcast_pending_mask, GFP_NOWAIT);
-	alloc_cpumask_var(&tick_broadcast_force_mask, GFP_NOWAIT);
+	zalloc_cpumask_var(&tick_broadcast_oneshot_mask, GFP_NOWAIT);
+	zalloc_cpumask_var(&tick_broadcast_pending_mask, GFP_NOWAIT);
+	zalloc_cpumask_var(&tick_broadcast_force_mask, GFP_NOWAIT);
 #endif
 }