genirq: Clear CPU mask in affinity_hint when none is provided

When an interrupt is disabled and torn down, the CPU mask returned
through affinity_hint right now is all CPUs. Also, for drivers that
don't provide an affinity_hint mask, this can be misleading. There
should be no hint at all, meaning an empty CPU mask.

[ tglx: use zalloc_cpumask_var instead of clearing it under the lock ]

Signed-off-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
Cc: davem@davemloft.net
Cc: arjan@linux.jf.intel.com
Cc: bhutchings@solarflare.com
LKML-Reference: <20100505205638.5426.87189.stgit@ppwaskie-hc2.jf.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/irq/proc.c

@@ -38,14 +38,12 @@ static int irq_affinity_hint_proc_show(struct seq_file *m, void *v)
 	unsigned long flags;
 	cpumask_var_t mask;
 
-	if (!alloc_cpumask_var(&mask, GFP_KERNEL))
+	if (!zalloc_cpumask_var(&mask, GFP_KERNEL))
 		return -ENOMEM;
 
 	raw_spin_lock_irqsave(&desc->lock, flags);
 	if (desc->affinity_hint)
 		cpumask_copy(mask, desc->affinity_hint);
-	else
-		cpumask_setall(mask);
 	raw_spin_unlock_irqrestore(&desc->lock, flags);
 
 	seq_cpumask(m, mask);