genirq: keep affinities set from userspace across free/request_irq()

Impact: preserve user-modified affinities on interrupts

Kumar Galak noticed that commit
18404756765c713a0be4eb1082920c04822ce588 (genirq: Expose default irq
affinity mask (take 3))

overrides an already set affinity setting across a free /
request_irq(). Happens e.g. with ifdown/ifup of a network device.

Change the logic to mark the affinities as set and keep them
intact. This also fixes the unlocked access to irq_desc in
irq_select_affinity() when called from irq_affinity_proc_write()

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/irq/proc.c b/kernel/irq/proc.c
index 4d161c7..d257e7d 100644
--- a/kernel/irq/proc.c
+++ b/kernel/irq/proc.c
@@ -62,7 +62,7 @@
 	if (!cpus_intersects(new_value, cpu_online_map))
 		/* Special case for empty set - allow the architecture
 		   code to set default SMP affinity. */
-		return irq_select_affinity(irq) ? -EINVAL : count;
+		return irq_select_affinity_usr(irq) ? -EINVAL : count;
 
 	irq_set_affinity(irq, new_value);